Updated on 2024/06/05

写真a

 
YONEMITSU Kenji
 
Organization
Faculty of Science and Engineering Professor
Other responsible organization
Physics Course of Graduate School of Science and Engineering, Master's Program
Physics Course of Graduate School of Science and Engineering, Doctoral Program
External link

Degree

  • Doctor of Science ( The University of Tokyo )

  • Master of Science ( The University of Tokyo )

Education

  • 1990.6
     

    東京大学物性研究所   研究生   others

  • 1990.3
     

    The University of Tokyo   Graduate School, Division of Science   doctor course   completed

  • 1987.3
     

    The University of Tokyo   Graduate School, Division of Science   master course   completed

  • 1985.3
     

    The University of Tokyo   Faculty of Science   graduated

  • 1981.3
     

    福岡県立小倉高等学校   graduated

Research History

  • 2012.4 - Now

    Chuo University   Faculty of Science and Engineering, Department of Physics   Professor

  • 2023.4 - 2023.9

    Osaka Metropolitan University   Graduate School of Engineering

  • 2022.4 - 2022.9

    Osaka Metropolitan University   School of Engineering

  • 2007.4 - 2012.3

    Institute for Molecular Science   Associate Professor

  • 2009.10 - 2010.3

    Yokohama National University   Graduate School of Engineering

  • 2008.10 - 2009.3

    Yokohama National University   Graduate School of Engineering

  • 1996.2 - 2007.3

    Institute for Molecular Science   Associate Professor

  • 2003.4 - 2004.3

    Kyoto University   Faculty of Science

  • 1999.10 - 2000.3

    Osaka City University   Faculty of Engineering

  • 1999.4 - 2000.3

    Nagoya University   Graduate School of Engineering

  • 1997.9 - 1998.3

    University of Tsukuba   Graduate School of Science and Technology

  • 1995.7 - 1996.1

    Tohoku University   Faculty of Engineering   Associate Professor

  • 1994.9 - 1995.6

    Tohoku University   Graduate School of Information Sciences   Assistant Professor

  • 1994.2 - 1994.9

    University of Georgia (USA) Center for Simulational Physics   Postdoctoral fellow

  • 1993.1 - 1994.2

    International Center for Theoretical Physics (Italy)   Postdoctoral fellow

  • 1990.6 - 1992.12

    Los Alamos National Laboratory (USA) Theoretical Division   Postdoctoral fellow

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Professional Memberships

  • 1991.3 - Now

    American Physical Society

  • 1986.9 - Now

    The Physical Society of Japan

Research Interests

  • 低次元電子系

  • 強相関電子系

  • 分子性物質

  • 有機導体

  • 光誘起相転移

  • Condensed molecular materials

  • nonequilibrium cooperative phenomena

  • strongly correlated electron systems

Research Areas

  • Natural Science / Mathematical physics and fundamental theory of condensed matter physics

  • Natural Science / Magnetism, superconductivity and strongly correlated systems

  • Natural Science / Semiconductors, optical properties of condensed matter and atomic physics

Papers

  • Light-induced large and tunable valley-selective Hall effect in a centrosymmetric system Reviewed

    Naoya Arakawa, Kenji Yonemitsu

    Physical Review B   109 ( 24 )   L241201 - (6 pages)   2024.6

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevB.109.L241201

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  • Symmetry-protected difference between spin Hall and anomalous Hall effects of a periodically driven multiorbital metal Reviewed

    Naoya Arakawa, Kenji Yonemitsu

    Communications Physics   6   43 - (8 pages)   2023.3

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    DOI: 10.1038/s42005-023-01153-9

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  • Photoinduced Pseudospin Polarization in a Three-Orbital Hubbard Model Reviewed

    Kenji Yonemitsu

    Journal of the Physical Society of Japan   91 ( 10 )   104702 - (14 pages)   2022.10

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    Authorship:Lead author, Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Society of Japan  

    DOI: 10.7566/JPSJ.91.104702

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  • Light-induced magnetization driven by interorbital charge motion in the spin-orbit assisted Mott insulator α-RuCl3 Reviewed

    T. Amano, Y. Kawakami, H. Itoh, K. Konno, Y. Hasegawa, T. Aoyama, Y. Imai, K. Ohgushi, Y. Takeuchi, Y. Wakabayashi, K. Goto, Y. Nakamura, H. Kishida, K. Yonemitsu, S. Iwai

    Physical Review Research   4 ( 3 )   L032032 - (6 pages)   2022.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    DOI: 10.1103/physrevresearch.4.l032032

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.4.L032032/fulltext

  • Petahertz charge dynamics in a correlated organic superconductor Reviewed

    Shinichiro Iwai, Yohei Kawakami, Hirotake Itoh, Kenji Yonemitsu

    Faraday Discussions   237   353 - 367   2022.6

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    Publishing type:Research paper (scientific journal)   Publisher:Royal Society of Chemistry (RSC)  

    Unconventional stimulated emission and second harmonic generation (SHG) in an ultrafast no-scattering time window are induced by a nearly single-cycle 6 fs near infrared electric field of 10 MV cm−1 in an organic superconductor (κ-(h-ET)2Cu[N(CN)2]Br).

    DOI: 10.1039/D2FD00004K

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  • Petahertz Correlated Electron Dynamics in an Organic Superconductor

    Shinichiro Iwai, Yohei Kawakami, Hirotake Itoh, Kenji Yonemitsu

    Butsuri   77   304 - 309   2022.5

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    Language:Japanese  

    DOI: 10.11316/butsuri.77.5_304

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  • Polarization-dependent magnetic properties of periodically driven α−RuCl3 Reviewed

    Naoya Arakawa, Kenji Yonemitsu

    Physical Review B   104 ( 21 )   214413 (22 pages)   2021.12

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    DOI: 10.1103/PhysRevB.104.214413

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.104.214413/fulltext

  • Mechanism for Synchronization of Charge Oscillations in Dimer Lattices Reviewed

    Kenji Yonemitsu, Philipp Werner

    Journal of the Physical Society of Japan   90 ( 4 )   044713 (8 pages) - 044713   2021.4

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    DOI: 10.7566/jpsj.90.044713

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  • Floquet engineering of Mott insulators with strong spin-orbit coupling Reviewed

    Naoya Arakawa, Kenji Yonemitsu

    Physical Review B   103 ( 10 )   L100408 (5 pages)   2021.3

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    DOI: 10.1103/physrevb.103.l100408

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.L100408/fulltext

  • Competition between Interactions and Randomness in Photoinduced Synchronization of Charge Oscillations on a Dimer Lattice Reviewed

    Toshiya Shimada, Kenji Yonemitsu

    Journal of the Physical Society of Japan   89 ( 8 )   084701 - 084701   2020.8

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    Authorship:Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Society of Japan  

    DOI: 10.7566/jpsj.89.084701

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  • Photoinduced dynamics of excitonic order and Rabi oscillations in the two-orbital Hubbard model Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    Physical Review B   102 ( 7 )   075118 (20 pages)   2020.8

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    DOI: 10.1103/physrevb.102.075118

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.102.075118/fulltext

  • Petahertz non-linear current in a centrosymmetric organic superconductor Reviewed

    Y. Kawakami, T. Amano, H. Ohashi, H. Itoh, Y. Nakamura, H. Kishida, T. Sasaki, G. Kawaguchi, H. M. Yamamoto, K. Yamamoto, S. Ishihara, K. Yonemitsu, S. Iwai

    Nature Communications   11   4138 (6 pages)   2020.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    DOI: 10.1038/s41467-020-17776-3

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    Other Link: http://www.nature.com/articles/s41467-020-17776-3

  • Photoinduced Dynamics of Commensurate Charge Density Wave in 1T-TaS2 Based on Three-Orbital Hubbard Model Reviewed

    T. N. Ikeda, H. Tsunetsugu, K. Yonemitsu

    Applied Sciences   9 ( 1 )   70 (13 pages)   2019.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.3390/app9010070

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  • Charge Oscillations Emerging after Application of an Intense Light Field to Superconductors on a Dimer Lattice Reviewed

    K. Yonemitsu

    Journal of the Physical Society of Japan   87 ( 12 )   124703 (9 pages)   2018.12

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    DOI: 10.7566/JPSJ.87.124703

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  • Strong light-field effects driven by nearly single-cycle 7fs light-field in correlated organic conductors Reviewed

    Y. Kawakami, H. Itoh, K. Yonemitsu, S. Iwai

    J. Phys. B: At. Mol. Opt. Phys.   51 ( 17 )   174005 (15 pages)   2018.9

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    DOI: 10.1088/1361-6455/aad40a

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  • Photoinduced enhancement of excitonic order in the two-orbital Hubbard model Reviewed

    Yasuhiro Tanaka, Manabu Daira, Kenji Yonemitsu

    Physical Review B   97 ( 11 )   115105 (9 pages)   2018.3

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    Photoinduced dynamics in an excitonic insulator is studied theoretically by using a two-orbital Hubbard model on the square lattice where the excitonic phase in the ground state is characterized by the BCS-BEC crossover as a function of the interorbital Coulomb interaction. We consider the case where the order has a wave vector Q=(0,0) and photoexcitation is introduced by a dipole transition. Within the mean-field approximation, we show that the excitonic order can be enhanced by the photoexcitation when the system is initially in the BEC regime of the excitonic phase, whereas it is reduced if the system is initially in the BCS regime. The origin of this difference is discussed from behaviors of momentum distribution functions and momentum-dependent excitonic pair condensation. In particular, we show that the phases of the excitonic pair condensation have an important role in determining whether the excitonic order is enhanced or not.

    DOI: 10.1103/PhysRevB.97.115105

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  • Photoinduced high-Frequency charge oscillations in dimerized systems Reviewed

    Kenji Yonemitsu

    Journal of the Physical Society of Japan   87 ( 4 )   044708 (8 pages)   2018

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    Photoinduced charge dynamics in dimerized systems is studied on the basis of the exact diagonalization method and the time-dependent Schrödinger equation for a one-dimensional spinless-fermion model at half filling and a two-dimensional model for κ-(bis[ethylenedithio]tetrathiafulvalene)2X [κ-(BEDT-TTF)2X] at three-quarter filling. After the application of a one-cycle pulse of a specifically polarized electric field, the charge densities at half of the sites of the system oscillate in the same phase and those at the other half oscillate in the opposite phase. For weak fields, the Fourier transform of the time profile of the charge density at any site after photoexcitation has peaks for finite-sized systems that correspond to those of the steady-state optical conductivity spectrum. For strong fields, these peaks are suppressed and a new peak appears on the high-energy side, that is, the charge densities mainly oscillate with a single frequency, although the oscillation is eventually damped. In the two-dimensional case without intersite repulsion and in the one-dimensional case, this frequency corresponds to charge-transfer processes by which all the bonds connecting the two classes of sites are exploited. Thus, this oscillation behaves as an electronic breathing mode. The relevance of the new peak to a recently found reflectivity peak in κ-(BEDT-TTF)2X after photoexcitation is discussed.

    DOI: 10.7566/JPSJ.87.044708

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  • Nonlinear charge oscillation driven by a single-cycle light field in an organic superconductor Reviewed

    Kawakami, Y, Amano, T, Yoneyama, Y, Akamine, Y, Itoh, H, Kawaguchi, G, Yamamoto, H. M, Kishida, H, Itoh, K, Sasaki, T, Ishihara, S, Tanaka, Y, Yonemitsu, K, Iwai, S

    Nature Photonics   12 ( 8 )   474 - 478   2018

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    DOI: 10.1038/s41566-018-0194-4

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  • High-Frequency Analysis of Effective Interactions and Bandwidth for Transient States after Monocycle Pulse Excitation of Extended Hubbard Model Reviewed

    Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   86 ( 6 )   064702 (8 pages)   2017.6

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    Using a high-frequency expansion in periodically driven extended Hubbard models, where the strengths and ranges of density-density interactions are arbitrary, we obtain the effective interactions and bandwidth, which depend sensitively on the polarization of the driving field. Then, we numerically calculate modulations of correlation functions in a quarter-filled extended Hubbard model with nearest-neighbor interactions on a triangular lattice with trimers after monocycle pulse excitation. We discuss how the resultant modulations are compatible with the effective interactions and bandwidth derived above on the basis of their dependence on the polarization of photoexcitation, which is easily accessible by experiments. Some correlation functions after monocycle pulse excitation are consistent with the effective interactions, which are weaker or stronger than the original ones. However, the photoinduced enhancement of anisotropic charge correlations previously discussed for the three-quarter-filled organic conductor alpha-(bis[ethylenedithio]-tetrathiafulvalene)(2)I-3 [alpha-(BEDT-TTF)(2)I-3] in the metallic phase is not fully explained by the effective interactions or bandwidth, which are derived independently of the filling.

    DOI: 10.7566/JPSJ.86.064702

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  • Polarization selectivity of charge localization induced by a 7-fs nearly single-cycle light field in an organic metal Reviewed

    Y. Kawakami, Y. Yoneyama, T. Amano, H. Itoh, K. Yamamoto, Y. Nakamura, H. Kishida, T. Sasaki, S. Ishihara, Y. Tanaka, K. Yonemitsu, S. Iwai

    PHYSICAL REVIEW B   95 ( 20 )   201105(R) (5 pages)   2017.5

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    Polarization selectivity of light-field-induced charge localization was investigated in an organic metal alpha-(BEDT-TTF)(2)I-3 with a triangular lattice. Dependences of transient reflectivity spectra on polarizations of the 7-fs pump and probe lights indicate that a short-range charge order (CO) is induced efficiently from the metallic phase for the pump polarization perpendicular to the 1010-type CO axis. A numerical solution of a time-dependent Schrodinger equation clarified that the 1010 CO is induced by field-induced re-distribution of charges cooperating with competing intersite Coulomb repulsions in the triangular lattice.

    DOI: 10.1103/PhysRevB.95.201105

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  • Photoinduced Enhancement of Anisotropic Charge Correlations on Triangular Lattices with Trimers Reviewed

    Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   86 ( 2 )   024711 (8 pages)   2017.2

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    To explore nontrivial photoinduced modulations of charge correlations, we theoretically study photoinduced dynamics in quarter-filled extended Hubbard models with competing intersite repulsive interactions on triangular lattices with trimers, where the end points are crystallographically equivalent. The exact diagonalization method is used and the time-dependent Schrdinger equation is numerically solved during and after photoexcitation. Time-averaged double occupancy and intersite density-density correlations can be interpreted as due to effective on-site and intersite repulsive interactions, respectively, relative to transfer energies. In the case where the intersite repulsive interactions compete with each other, the anisotropy of their effective interactions can be enhanced with the help of the trimers, irrespective of whether the trimers are linear or bent. In particular, in the case where the arrangement of the trimers is close to that in alpha-(bis[ethylenedithio]-tetrathiafulvalene)(2)I-3 [alpha-(BEDT-TTF)(2)I-3] in the metallic phase, the effective on-site repulsion is enhanced relative to the transfer energies. The relevance of this theoretical finding to the experimentally observed optical freezing of charge motion is discussed.

    DOI: 10.7566/JPSJ.86.024711

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  • Light-field induced reduction of "plasma" frequency in organic conductor Reviewed

    Y. Naitoh, S. Iwai, Y. Kawakami, H. Itoh, S. Ishihara, K. Yamamoto, K. Yonemitsu

    Optics InfoBase Conference Papers F20-UP   2016.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OSA  

    DOI: 10.1364/up.2016.utu4a.26

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  • Optical freezing of charge motion in organic metal Reviewed

    S. Iwai, Y. Naitoh, Y. Kawakami, H. Itoh, S. Ishihara, K. Yamamoto, H. Kishida, K. Yonemitsu

    Optics InfoBase Conference Papers F20-UP   2016.7

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    DOI: 10.1364/up.2016.utu4a.24

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  • Ultrafast response of plasmalike reflectivity edge in (TMTTF)2AsF6 driven by a 7-fs 1.5-cycle strong-light field Reviewed

    Y. Naitoh, Y. Kawakami, T. Ishikawa, Y. Sagae, H. Itoh, K. Yamamoto, T. Sasaki, M. Dressel, S. Ishihara, Y. Tanaka, K. Yonemitsu, S. Iwai

    Physical Review B   93 ( 16 )   165126 (5 pages)   2016.4

  • Electron Correlation after Pulse Excitation and High-Frequency Expansion within Floquet Theory for α-(BEDT-TTF)2I3

    Yonemitsu Kenji

    Meeting Abstracts of the Physical Society of Japan   71   1233 - 1233   2016

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    Language:Japanese   Publisher:The Physical Society of Japan  

    DOI: 10.11316/jpsgaiyo.71.2.0_1233

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  • Ultrafast critical phenomena near the metal-Mott insulator phase boundary in κ-type ET salts II

    Kawakami Y., Naitoh Y., Kato T., Yoneyama Y., Itoh H., Yoneyama N., Sasaki T., Yonemitsu K., Ishihara S., Iwai S.

    Meeting Abstracts of the Physical Society of Japan   71   1240 - 1240   2016

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    Language:Japanese   Publisher:The Physical Society of Japan  

    DOI: 10.11316/jpsgaiyo.71.2.0_1240

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  • Phase Separation Induced by Symmetric Monocycle Optical Pulse in Extended Hubbard Models Reviewed

    Hiroki Yanagiya, Yasuhiro Tanaka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   84 ( 9 )   094705 (9 pages)   2015.9

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    Many-electron dynamics induced by a symmetric monocycle electric-field pulse of large amplitude is theoretically investigated in one-and two-dimensional half-filled extended Hubbard models on regular lattices (i.e., without dimerization) using the exact diagonalization method for small systems and the Hartree-Fock approximation for large systems. The formation of a negative-temperature state and the change from repulsive interactions to effective attractive interactions are shown to be realized for a wide region of the field amplitude and the excitation energy. For a nonnegligible intersite repulsive interaction, the numerical results are consistent with the fact that the phase separation between charge-rich and charge-poor regions is caused by the corresponding effective attraction.

    DOI: 10.7566/JPSJ.84.094705

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  • Negative-Temperature State Formed and Interactions Inverted by Symmetric Monocycle Optical Pulse Excitation Reviewed

    Kenji Yonemitsu, Keita Nishioka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   84 ( 5 )   054702 (10 pages)   2015.5

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    The excited state dynamics of correlated electron and electron-phonon systems triggered by an oscillating electric-field pulse of large amplitude are theoretically investigated. A "negative-temperature" state and inversion of electron-electron and electron-phonon interactions are induced even by a symmetric monocycle pulse. This fact is numerically demonstrated, using the exact diagonalization method, in a band-insulator phase of one-dimensional three-quarter-filled strongly dimerized extended Peierls-Hubbard and Holstein models. When the total-energy increment is maximized as a function of the electric field amplitude, the occupancy of the bonding and antibonding orbitals is inverted to produce a negative-temperature state. Around this state, the dependences of time-averaged electron-electron and electron-phonon correlation functions on interaction parameters are opposite to those in the ground state.

    DOI: 10.7566/JPSJ.84.054702

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  • Spontaneous formation of correlated charge coherence induced by 1.5-cycle pulse in 1-D organic metal (TMTTF)2AsF6 Reviewed

    T. Ishikawa, Y. Sagae, Y. Naito, J. Ichimura, Y. Kawakami, H. Itoh, K. Yamamoto, K. Yakushi, S. Ishihara, T. Sasaki, K. Yonemitsu, S. Iwai

    Springer Proceedings in Physics   162   244 - 247   2015

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    Ultrafast optical response of organic metal (TMTTF)2AsF6 induced by 1.5 cycle (7 fs) infrared pulse was investigated. Intense coherent oscillation of correlated charge (18 fs) grows in the time scale of 50 fs, reflecting the spontaneous- formation of the electronic coherence before the electronic thermalization.

    DOI: 10.1007/978-3-319-13242-6_59

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  • 22pPSB-28 Sources of Negative Differential Resistance in Band Insulators Attached to Electrodes

    Tanaka Y., Yonemitsu K.

    Meeting Abstracts of the Physical Society of Japan   70   3062 - 3062   2015

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    Language:Japanese   Publisher:The Physical Society of Japan (JPS)  

    DOI: 10.11316/jpsgaiyo.70.1.0_3062

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  • 21aCP-3 Stability and Photoinduced Dynamics of Charge-Density-Wave State in TaS_2

    Fujinuma R., Yonemitsu K., Tanaka Y.

    Meeting Abstracts of the Physical Society of Japan   70   1432 - 1432   2015

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    Language:Japanese   Publisher:The Physical Society of Japan (JPS)  

    DOI: 10.11316/jpsgaiyo.70.1.0_1432

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  • 17aCF-4 Negative-Temperature State, Inversion of Interactions, and Dynamical Localization

    Yonemitsu Kenji

    Meeting Abstracts of the Physical Society of Japan   70   1208 - 1209   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_1208

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  • 22pCP-9 Inverted Interactions and Phase Separation Triggered by Strong Optical Electric Field in the Extended Hubbard Model

    Yanagiya H., Tanaka Y., Yonemitsu K.

    Meeting Abstracts of the Physical Society of Japan   70   1521 - 1521   2015

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    Language:Japanese   Publisher:The Physical Society of Japan (JPS)  

    DOI: 10.11316/jpsgaiyo.70.1.0_1521

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  • Roles of Potential Gradient and Electrode Bandwidth on Negative Differential Resistance in One-Dimensional Band Insulator Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 12 )   124704 (4 pages)   2014.12

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    A negative differential resistance (NDR) in a one-dimensional band insulator attached to electrodes is investigated. We systematically examine the effects of an electrode bandwidth and a potential distribution inside the insulator on current-voltage characteristics. We show that, in uncorrelated systems, the NDR is generally caused by a linear potential gradient as well as by a finite electrode bandwidth. In particular, the former reduces the effective bandwidth of the insulator for elastic tunneling by tilting its energy band, so that it brings about the NDR even in the limit of large electrode bandwidth.

    DOI: 10.7566/JPSJ.83.124704

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  • Optical freezing of charge motion in an organic conductor Reviewed

    Takahiro Ishikawa, Yuto Sagae, Yota Naitoh, Yohei Kawakami, Hirotake Itoh, Kaoru Yamamoto, Kyuya Yakushi, Hideo Kishida, Takahiko Sasaki, Sumio Ishihara, Yasuhiro Tanaka, Kenji Yonemitsu, Shinichiro Iwai

    NATURE COMMUNICATIONS   5   5528 (6 pages)   2014.11

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    Dynamical localization, that is, reduction of the intersite electronic transfer integral t by an alternating electric field, E(omega), is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3MVcm(-1) instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor alpha-(bis[ethylenedithio]-tetrathiafulvalene) I-2(3). A large reflectivity change of >25% and a coherent charge oscillation along the time axis reflect the opening of the charge ordering gap in the metallic phase. This optical freezing of charges, which is the reverse of the photoinduced melting of electronic orders, is attributed to the similar to 10% reduction of t driven by the strong, high-frequency (omega >= t/(h) over bar) electric field.

    DOI: 10.1038/ncomms6528

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  • Coherent dynamics of photoinduced phase formation in a strongly correlated organic crystal Reviewed

    Yoshitaka Matsubara, Sho Ogihara, Jiro Itatani, Nobuya Maeshima, Kenji Yonemitsu, Tadahiko Ishikawa, Yoichi Okimoto, Shin-ya Koshihara, Takaaki Hiramatsu, Yoshiaki Nakano, Hideki Yamochi, Gunzi Saito, Ken Onda

    PHYSICAL REVIEW B   89 ( 16 )   161102(R) (5 pages)   2014.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    The photoinduced phase formation in a strongly correlated crystal (EDO-TTF)(2)PF6 (EDO-TTF: 4,5-ethylenedioxytetrathiafulvalene) is investigated using a 12 fs laser pulse. The formation time is determined as 40 fs with observation of coherence of electron-phonon coupled excited states prior to formation. The temperature-independent dephasing time is determined as similar to 22 fs up to 180 K and the frequency of phonon oscillation is similar to 38 THz, corresponding to the intramolecular vibrations in EDO-TTF. The phase formation is coherently controlled by relative-phase-controlled two-pulse excitation.

    DOI: 10.1103/PhysRevB.89.161102

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  • Intramolecular Orbital Excitations and Frequency Modulation of Molecular Vibrations during Photoinduced Charge-Order Melting in Et$_2$Me$_2$Sb[Pd(dmit)$_2$]$_2$ Reviewed

    K. Nishioka, K. Yonemitsu

    JPS Conference Proceedings   1   012044 (4 pages)   2014.3

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  • Intra- and Interdimer Transfer Integrals Effectively Modified by Pulsed and Continuous-Wave Lasers for Controlling Charge Transfers in Molecular Crystals Reviewed

    Keita Nishioka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 2 )   024706 (9 pages)   2014.2

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    We theoretically study the field-intensity dependence of charge transfers driven by continuous-wave and pulsed lasers in a two-dimensional crystal consisting of molecular dimers by numerically solving the time-dependent Schrodinger equation for an extended Hubbard model. Generally, electronic transfer integrals are regarded as renormalized when an oscillating external field is applied, as far as the electronic dynamics averaged over the oscillation period is concerned. The cases where effective transfer integrals vanish are known as dynamic localization. Interdimer charge transfers driven by continuous-wave lasers are thus governed by effective interdimer transfer integrals. After the field is switched off, the dynamic localization is no longer relevant. Then, we show that interdimer charge transfers driven by pulsed lasers of energy resonant with an intradimer transition are governed by an effective intradimer transfer integral. The total-energy increment depends on how the intradimer transfer integral is renormalized. The same holds for interdimer charge transfers. This interdimer dynamics governed by effective intradimer parameters is evident even for one-and two-cycle pulses, suggesting possible control of photoinduced charge-order melting.

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  • Charge order and possible bias-induced metastable state in the organic conductor β-(meso-DMBEDT-TTF)2PF6: Effects of structural distortion Reviewed

    Y. Tanaka, K. Yonemitsu

    Journal of Physics Condensed Matter   25 ( 46 )   465603 (6pp)   2013.11

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    We theoretically investigate charge order and nonlinear conduction in the quasi-two-dimensional organic conductor β-(meso-DMBEDT-TTF) 2PF6 (DMBEDT-TTF=dimethylbis(ethylenedithio) tetrathiafulvalene). Within the Hartree-Fock approximation, we study the effects of structural distortion on the experimentally observed checkerboard charge order and its bias-induced melting by using an extended Hubbard model with Peierls- and Holstein-types of electron-lattice interactions. The structural distortion is important in realizing the charge order. The current-voltage characteristics obtained by a nonequilibrium Green's function method indicate that a charge-ordered insulating state changes into a conductive state. Although the charge order and lattice distortions are largely suppressed at a threshold voltage, they remain finite even in the conductive state. We discuss the relevance of the results to experimental observations, especially to a possible bias-induced metastable state. © 2013 IOP Publishing Ltd.

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  • Intra- and Interdimer Electron-Phonon Concerted Mechanism of Photoinduced Charge-Order Melting in Metal Complex Et2Me2Sb[Pd(dmit)(2)](2) Reviewed

    Keita Nishioka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 9 )   094716 (10 pages)   2013.9

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    To elucidate interconnections of intra- and interdimer electronic and phonon degrees of freedom during the photoinduced melting of charge order in the quasi-two-dimensional metal complex Et2Me2Sb[Pd(dmit)(2)](2), we study the photoinduced charge dynamics and transient C C and intermonomer vibration frequencies in an extended Peierls-Hubbard model. The charge order consisting of neutral and divalent dimers is realized by strong intradimer electron-phonon interactions. After photoexcitation inducing intradimer electronic transitions, the structures of the neutral and divalent dimers are changed into that of monovalent dimers by couplings between electrons and intermonomer vibrations. Then, the electronic energy levels of these dimers resonate with each other and a large charge transfer occurs between them. Some C=C vibrations are selectively coupled with intradimer charge transfer, while other C=C vibrations with interdimer charge transfer. During the charge-order melting, the frequencies of the C=C vibrations are modulated and deviate from the charge-density-phonon-frequency relations in the equilibrium state. In the hierarchical structure involving the intra-and interdimer electron-phonon degrees of freedom, their concerted action promotes the charge-order melting.

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  • Current-voltage characteristics and breakdown mechanism in one-dimensional band and mott insulators attached to electrodes Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    Journal of the Korean Physical Society   62 ( 12 )   2164 - 2167   2013.7

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    The current-voltage characteristics and mechanism of bias-induced breakdown in one-dimensional models for band and Mott insulators are investigated theoretically by using nonequilibrium Green's functions. We attach the models to metallic electrodes, the effects of which are incorporated into the self-energy. For the models of both the band and the Mott insulators with lengths L C, the bias voltage induces a breakdown of the insulating state, and the breakdown mechanism shows a crossover depending on L C. When L C is smaller than the correlation length ξ = W/Δ, the threshold is determined basically by the bias V th ∼ Δ, where W and Δ are the bandwidth and the energy gap, respectively. For systems with L C ≫ ξ, the threshold is governed by the electric field, V th/L C, which is consistent with a Landau-Zener-type breakdown V th/L C ∝ Δ2/W. © 2013 The Korean Physical Society.

    DOI: 10.3938/jkps.62.2164

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  • Current-Induced Cooling Phenomenon in a Two-Dimensional Electron Gas Under a Magnetic Field Reviewed

    Naomi Hirayama, Akira Endo, Kazuhiro Fujita, Yasuhiro Hasegawa, Naomichi Hatano, Hiroaki Nakamura, Ryoen Shirasaki, Kenji Yonemitsu

    JOURNAL OF LOW TEMPERATURE PHYSICS   172 ( 1-2 )   132 - 153   2013.7

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    We investigate the spatial distribution of temperature induced by a dc current in a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We numerically calculate the distributions of the electrostatic potential I center dot and the temperature T in a 2DEG enclosed in a square area surrounded by insulated-adiabatic (top and bottom) and isopotential-isothermal (left and right) boundaries (with I center dot (left)< I center dot (right) and T (left)=T (right)), using a pair of nonlinear Poisson equations (for I center dot and T) that fully take into account thermoelectric and thermomagnetic phenomena, including the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. We find that, in the vicinity of the left-bottom corner, the temperature becomes lower than the fixed boundary temperature, contrary to the naive expectation that the temperature is raised by the prevalent Joule heating effect. The cooling is attributed to the Ettingshausen effect at the bottom adiabatic boundary, which pumps up the heat away from the bottom boundary. In order to keep the adiabatic condition, downward temperature gradient, hence the cooled area, is developed near the boundary, with the resulting thermal diffusion compensating the upward heat current due to the Ettingshausen effect.

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  • Theory of MMX-chain compounds Reviewed

    Kenji Yonemitsu

    Material Designs and New Physical Properties in MX- and MMX-Chain Compounds   9783709113172   243 - 264   2013.6

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    Mechanisms of a variety of charge and lattice ordered phases observed in MMX compounds are theoretically studied by using a one-dimensional two-band three-quarter-filled extended Peierls-Hubbard model. In R4[Pt2(pop)4I]nH2O [R = Na, K, NH4, (CH3(CH2)7)2NH2, etc., pop = P2O5H 2 2- ] containing charged MMX chains, three electronic phases are suggested by experiments. We find that the variation of the electronic phases originates not only from competition between site-diagonal electron-lattice and electron-electron interactions but also from competition between short-range and long-range electron-electron interactions. On the other hand, in Pt2(RCS2)4I (R = CH3, n-C4H9) containing neutral MMX chains, a site-off-diagonal electron-lattice interaction and the absence of counterions are found to be crucial to produce the alternate-charge-polarization phase. The optical conductivity spectra are also studied, which directly reflect the electronic phases. A photoinduced transition has been found in a MMX compound, R4[Pt2(pop)4I]nH2O (R = (C2H5)2NH2). Its mechanism is theoretically studied by solving the time-dependent Schrödinger equation. Above a threshold in the photoexcitation intensity, a transition takes place from the charge-density-wave phase to the charge-polarization phase. The threshold-intensity dependence on the relative stability of these phases is explained qualitatively by their diabatic potentials. However, the transition in the opposite direction is hardly realized and needs careful consideration of different charge transfer processes.

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  • Normal-Mode Analysis for Intra- and Intermolecular Electron-Phonon Coupled Systems with Charge-Ordered and Dimer-Mott Ground States Reviewed

    Keita Nishioka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 2 )   024701 (11 pages)   2013.2

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    We have theoretically studied the ground-state properties of the molecular compound, Et2Me2Sb[Pd(dmit)(2)](2), which shows a dimer-Mott character in Pd(dmit)(2) layers at high temperature and a charge order mainly stabilized by an electron-phonon interaction at low temperature. An effective extended Peierls-Hubbard model is constructed with intra- and intermolecular electronic and phonon degrees of freedom. Using mean-field approximation, the energies and optimized structures are calculated for isolated neutral, monovalent, divalent Pd(dmit)(2) dimers and their two-dimensional crystallized states. The optical conductivities of the crystallized states are calculated by a single-configuration interaction method. For intramolecular vibrations, normal-mode analysis is performed, which is useful to explain the recent experimental results. Molecular vibrations with different symmetries are coupled to different combinations of electrons and holes within a molecule, so that their frequencies depend on the molecular charge in different manners. This information will be useful to analyze photoinduced transient states, where the relation between their frequencies and the molecular charge is modified from the equilibrium counterpart.

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  • Transport-Coefficient Dependence of Current-Induced Cooling Effect in a Two-Dimensional Electron Gas Reviewed

    Naomi Hirayama, Akira Endo, Kazuhiro Fujita, Yasuhiro Hasegawa, Naomichi Hatano, Hiroaki Nakamura, Ryoen Shirasaki, Kenji Yonemitsu

    JOURNAL OF ELECTRONIC MATERIALS   41 ( 6 )   1535 - 1539   2012.6

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    The dependence of the current-induced cooling effect on the electron mobility (e) is explored for a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We calculate the distributions of the electrochemical potentials and the temperatures under a magnetic field, fully taking account of thermoelectric and thermomagnetic phenomena. Whereas the electrochemical potential and the electric current remain qualitatively unchanged, the temperature distribution exhibits drastic mobility dependence. The lower-mobility system has cold and hot areas at opposite corners, which results from the heat current brought about by the Ettingshausen effect in the vicinity of the adiabatic boundaries. The cooling effect is intensified by an increase in (e). Intriguingly, the cold and hot areas change places with each other as the mobility (e) is further increased. This is because the heating current on the adiabatic edges due to the Righi-Leduc effect exceeds that due to the Ettingshausen effect in the opposite direction.

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  • Roles of molecular vibrations in photoinduced insulator-to-metal and neutral-to-ionic transitions Reviewed

    Kenji Yonemitsu

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   249 ( 5 )   975 - 978   2012.5

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    The roles of molecular vibrations during photoinduced phase transitions in strongly correlated electron systems are theoretically studied on the basis of the time evolution of the exact many-electron and many-electronphonon wave functions in extended HolsteinPeierlsHubbard models. For the transition from a Coulomb-driven charge-ordered insulator to a metal, molecular vibrations interfere with charge transfers between neighboring molecules. For the transition from a neutral paraelectric state to an ionic ferroelectric state, they enhance the amplitude of ionicity modulation. They stabilize the initial phase in both cases, but their quantum nature is pronounced only in the former case.

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  • Two-pulse excitation for efficient formation of an sp(3) nanodomain with frozen shear in a graphite crystal Reviewed

    Keita Nishioka, Keiichiro Nasu, Kenji Yonemitsu

    JOURNAL OF PHYSICS-CONDENSED MATTER   24 ( 20 )   205402 (6pp)   2012.5

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    We propose a two-pulse excitation to efficiently form a novel sp(3)-bonded nanosize domain with frozen shear in a graphite crystal. This sp(3) structure is well stabilized by shear displacement between two neighboring graphite layers. The shearing motion is induced transiently by the first laser pulse, and is frozen by the second pulse before disappearing, resulting in the efficient formation of the sp(3)-bonded domain with frozen shear. We show this dynamical process qualitatively by molecular dynamics calculations.

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  • Dimerization-induced spin-charge coupling in one-dimensional Mott insulators revealed by femtosecond reflection spectroscopy of Rb-tetracyanoquinodimethane salts Reviewed

    H. Uemura, N. Maeshima, K. Yonemitsu, H. Okamoto

    Physical Review B - Condensed Matter and Materials Physics   85 ( 12 )   125112 (7 pages)   2012.3

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    Effects of lattice dimerizations on charge dynamics in one-dimensional (1D) half-filled Mott insulators were studied using an organic compound, Rb-tetracyanoquinodimethane (TCNQ). First, we investigated the presence of the dimeric molecular displacements by the measurements of polarized Raman spectra and the time evolutions of photoinduced reflectivity changes. The results indicate that Rb-TCNQ shows a spin-Peierls-like structural phase transition and molecular dimerization occurs below 220 K. Second, we performed femtosecond reflection spectroscopy from visible to infrared regions down to 0.1 eV on Rb-TCNQ in both the low-temperature phase with dimerization and the high-temperature phase without dimerization. The results revealed that the molecular dimerization causes splitting of midgap absorption due to photocarriers. Theoretical calculations by the density-matrix renormalization group method reveal that low- and high-energy midgap absorptions are due to pure charge excitation and spin-charge-coupled excitation, respectively, of polarons stabilized by the electron-lattice interaction. This indicates that dimerization breaks the spin-charge separation characteristic of 1D Mott insulators with large electron correlation. © 2012 American Physical Society.

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  • Theory of Photoinduced Phase Transitions in Molecular Conductors: Interplay Between Correlated Electrons, Lattice Phonons and Molecular Vibrations Reviewed

    Kenji Yonemitsu

    CRYSTALS   2 ( 1 )   56 - 77   2012.3

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    Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1) The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2) The organic salts theta-(BEDT-TTF)(2)RbZn(SCN)(4) and alpha-(BEDT-TTF)(2)I-3 show transitions from a charge-ordered insulator to a metal. Lattice phonons make this photoinduced transition hard for the former salt only. Molecular vibrations interfere with intermolecular transfers of correlated electrons at an early stage; (3) The organic salt kappa-(d-BEDT-TTF)(2)Cu[N(CN)(2)]Br shows a transition from a Mott insulator to a metal. Lattice phonons modulating intradimer transfer integrals enable photoexcitation-energy-dependent transition pathways through weakening of effective interaction and through introduction of carriers.

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  • Interplay between Correlated Electrons and Quantum Phonons in Charge-Ordered and Mott-Insulating Organic Compounds Reviewed

    K. Yonemitsu, N. Maeshima, Y. Tanaka

    ACTA PHYSICA POLONICA A   121 ( 2 )   372 - 374   2012.2

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    At an early stage of the photoinduced transition from an insulator to a metal in quasi-two-dimensional organic conductors, a coherent motion of electrons is observed in a charge-ordered insulator, but not so far in a Mott insulator. The mechanisms of these different photoinduced charge dynamics are theoretically studied by numerical solutions to the time-dependent Schrodinger equation for exact many-electron-phonon wave functions on small clusters of model systems. We use two-dimensional three-quarter-filled extended Holstein-Hubbard models on anisotropic triangular lattices. For a charge-ordered insulator on a lattice simplified from the structure of alpha-(BEDT-TTF)(2)I-3, we indeed find a low-energy collective electronic motion coupled with quantum phonons even if the energy of photoexcitation is away from this energy. For a Mott insulator on a lattice simplified from the structure of kappa-(BEDT-TTF)(2)X, however, such a collective motion does not appear, and quantum phonons are hardly excited.

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  • Theory of photoinduced melting of charge order in Et2Me2Sb[Pd(dmit)(2)](2) Reviewed

    Keita Nishioka, Kenji Yonemitsu

    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 5   9 ( 5 )   1213 - 1215   2012

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    We have theoretically studied photoinduced melting in a charge-separated (CS) phase of the dimeric radical anion salt, Et2Me2Sb[Pd(dmit)(2)](2), by using an extended Peierls-Hubbard model with intra-molecular degrees of freedom and the mean-field approximation. Model parameters are determined to reproduce the ground-state properties of neutral, monovalent, and divalent dimers, as well as their crystallized states.
    We have calculated the dynamics of a photoexcited state in the CS phase by solving the time-dependent Schrodinger equation. Neutral and divalent dimers are changed into a monovalent state after photoexcitation, resulting in the melting of charge order. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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  • Theory of nonlinear conduction for charge-ordered states in quasi-two-dimensional organic conductors Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 5   9 ( 5 )   1186 - 1188   2012

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    Nonlinear conduction in quasi-two-dimensional organic conductors partial derivative-(BEDT-TTF)(2)X [BEDTTTF= bis(ethylenedithio)tetrathiafulvalene] is investigated theoretically. By using a nonequilibrium Green's function method, an extended Peierls-Hubbard model attached to metallic electrodes is studied within the mean-field approximation. We show that in a coexistent state of stripe-type and nonstripe 3-fold charge orders, the former charge order is completely suppressed by the applied bias, whereas the latter charge order survives. This leads to selective melting of charge order of different origins. The disappearance of the stripe-type charge order largely alters the conduction behavior, which is consistent with the experimental findings. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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  • Renormalization of hopping integrals in coexistence phase of stripe and d-wave superconductivity in two-dimensional Hubbard model Reviewed

    Mitake Miyazaki, Kunihiko Yamaji, Takashi Yanagisawa, Kenji Yonemitsu

    ADVANCES IN SUPERCONDUCTIVITY XXIV   27   64 - 67   2012

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    We have performed a variational Monte Carlo simulation on a two-dimensional Hubbard model with first-and second-neighbor hopping terms in order to study the coexistence state of a static stripe state and a modulated d-wave superconductivity in the under-doped cuprates. In addition to a Gutzwiller, a Jastrow and a doublon-holon correlation effects, the band-renormalization effect was considered in the trial wave function. The condensation energies of an 8-period stripe state was computed as a function of a Coulomb energy under the hole-density x=1/8. Our results reveal that the renormalization of higher hopping parameters due to the strong correlation effect enhances the one-dimensional hole motion on a quarter-filled band in the stripe state, and brings quasi-Fermi surface close to the magnetic zone boundary in the coexistence state. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of ISS Program Committee

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  • Nonlinear Conduction by Melting of Stripe-Type Charge Order in Organic Conductors with Triangular Lattices Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   80 ( 10 )   103702 (4 pages)   2011.10

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    We theoretically discuss the mechanism for the peculiar nonlinear conduction in quasi-two-dimensional organic conductors theta-(BEDT-TTF)(2)X [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] through the melting of stripe-type charge order. An extended Peierls-Hubbard model attached to metallic electrodes is investigated by a nonequilibrium Green's function technique. A novel current-voltage characteristic appears in a coexistent state of stripe-type and nonstripe 3-fold charge orders, where the applied bias melts mainly the stripe-type charge order through the reduction of lattice distortion, whereas the 3-fold charge order survives. These contrastive responses of the two different charge orders are consistent with the experimental observations.

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  • Photoexcitation-Energy-Dependent Transition Pathways from a Dimer Mott Insulator to a Metal Reviewed

    Kenji Yonemitsu, Satoshi Miyashita, Nobuya Maeshima

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   80 ( 8 )   084710 (5 pages)   2011.8

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    We theoretically study pump-photon-energy-dependent pathways of a photoinduced dimer-Mott-insulator-to-metal transition, on the basis of numerical solutions to the time-dependent Schrodinger equation for the exact many-body wave function of a two-dimensional three-quarter-filled extended Peierls-Hubbard model. When molecular degrees of freedom inside a dimer are utilized, photoexcitation can weaken the effective interaction or increase the density of photocarriers. In the organic dimer Mott insulator, kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, the intradimer and the interdimer charge-transfer excitations have broad bands that overlap with each other. Even in this disadvantageous situation, the photoinduced conductivity change depends largely on the pump photon energy, confirming the two pathways recently observed experimentally. The characteristic of each pathway is clarified by calculating the modulation of the effective interaction and the number of carriers involved in low-energy optical excitations. The pump-photon-energy-dependent pathways are confirmed to be realized from the finding that, although the effective interaction is always and slowly weakened, the introduction of carriers is sensitive to the pump-photon energy and proceeds much faster.

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  • Effects of Lattice and Molecular Phonons on Photoinduced Neutral-to-Ionic Transition Dynamics in Tetrathiafulvalene-p-chloranil Reviewed

    Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   80 ( 8 )   084707 (7 pages)   2011.8

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    For electronic states and photoinduced charge dynamics near the neutral-ionic transition in the mixed-stack charge-transfer complex tetrathiafulvalene-p-chloranil (TTF-CA), we review the effects of Peierls coupling to lattice phonons modulating transfer integrals and Holstein couplings to molecular vibrations modulating site energies. The former stabilizes the ionic phase and reduces discontinuities in the phase transition, while the latter stabilizes the neutral phase and enhances the discontinuities. To reproduce the experimentally observed ionicity, optical conductivity and photoinduced charge dynamics, both couplings are quantitatively important. In particular, strong Holstein couplings to form the highly-stabilized neutral phase are necessary for the ionic phase to be a Mott insulator with large ionicity. A comparison with the observed photoinduced charge dynamics indicates the presence of strings of lattice dimerization in the neutral phase above the transition temperature.

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  • Quantum Oscillations of Thermoelectric Effects in a Pseudo-one-dimensional Electron Gas With a Spin-Orbit Interaction Reviewed

    Hiroaki Nakamura, Naomichi Hatano, Ryoen Shirasaki, Naomi Hirayama, Kenji Yonemitsu

    JOURNAL OF ELECTRONIC MATERIALS   40 ( 5 )   601 - 605   2011.5

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    We consider thermoelectric effects in a pseudo-one-dimensional electron gas (P1DEG) with a spin-orbit interaction (SOI). The SOI splits the dispersion relation of the P1DEG into subbands with an energy gap. We find quantum oscillations in transport coefficients, which coincide with the locations of the subband edges, as a function of the electrochemical potential.

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  • Temperature Distribution in Two-Dimensional Electron Gases under a Strong Magnetic Field Reviewed

    Naomi Hirayama, Akira Endo, Kazuhiro Fujita, Yasuhiro Hasegawa, Naomichi Hatano, Hiroaki Nakamura, Ryoen Shirasaki, Kenji Yonemitsu

    JOURNAL OF ELECTRONIC MATERIALS   40 ( 5 )   529 - 532   2011.5

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    Two-dimensional electron gases having an electrochemical potential gradient under a magnetic field are numerically examined using the finite-difference method. The temperature, voltage, electric current, and heat flux are calculated from transport equations describing thermoelectric and thermomagnetic effects, namely the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. The results show that a magnetic field distorts equipotential lines and generates an uneven temperature distribution. In particular, a part of the system is found to become colder than the temperature of the heat baths. The cooling effect under a strong magnetic field is due primarily to the Ettingshausen and Hall effects.

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  • Crossover from bias-induced to field-induced breakdown in one-dimensional band and Mott insulators attached to electrodes Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    PHYSICAL REVIEW B   83 ( 8 )   085113 (11 pages)   2011.2

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    Nonequilibrium states induced by an applied bias voltage (V) and the corresponding current-voltage characteristics of one-dimensional models describing band and Mott insulators are investigated theoretically by using nonequilibrium Green's functions. We attach the models to metallic electrodes, the effects of which are incorporated into the self-energy. Modulation of the electron density and the scalar potential coming from the additional long-range interaction are calculated self-consistently within the Hartree approximation. For both models of band and Mott insulators with length L-C, the bias voltage induces a breakdown of the insulating state, the threshold of which shows a crossover depending on L-C. It is determined basically by the bias V-th similar to Delta for L-C smaller than the correlation length xi = W/Delta, where W denotes the bandwidth and Delta denotes the energy gap. For systems with LC >> xi, the threshold is governed by the electric field V-th/L-C, which is consistent with a Landau-Zener-type breakdown V-th/L-C proportional to Delta(2)/W. We demonstrate that the spatial dependence of the scalar potential is crucially important for this crossover by showing the case without the scalar potential, where the breakdown occurs at V-th similar to Delta regardless of the length L-C.

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  • Photoinduced insulator-to-metal transition dynamics in models for quasi-two-dimensional organic conductors Reviewed

    Kenji Yonemitsu, Yasuhiro Tanaka, Satoshi Miyashita, Nobuya Maeshima

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   248 ( 2 )   486 - 490   2011.2

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    Photoinduced transition dynamics is studied in extended Peierls-Hubbard models for organic BEDT-TTF salts on anisotropic triangular lattices. For theta- and alpha-type salts, the lattice distortion pattern in the charge-ordered ground state governs the easiness of the insulator-to-metal transition. For K-type salts, the energy of photoexcitation in the dimer-Mott phase determines whether the insulator-to-metal transition is controlled by the bandwidth or the band filling. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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  • Photoinduced dynamics of the multi-orbital Hubbard model Reviewed

    Nobuya Maeshima, Ken-ichi Hino, Kenji Yonemitsu

    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 1   8 ( 1 )   213 - 216   2011

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    We investigate photoinduced dynamical properties of the one-dimensional two-orbital degenerate Hubbard model by calculating the time-dependent many-electron wave function. The transient optical response spectra around the charge-transfer peak show characteristic coherent oscillations, which can be attributed to the Raman-active orbital excitations (orbitons). An analysis for the oscillating component shows that the photoinduced oscillations are caused by the quantum interference between photogenerated states. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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  • Early-Stage Dynamics of Light-Matter Interaction Leading to the Insulator-to-Metal Transition in a Charge Ordered Organic Crystal Reviewed

    Y. Kawakami, T. Fukatsu, Y. Sakurai, H. Unno, H. Itoh, S. Iwai, T. Sasaki, K. Yamamoto, K. Yakushi, K. Yonemitsu

    PHYSICAL REVIEW LETTERS   105 ( 24 )   246402 (4 pages)   2010.12

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    Ultrafast dynamics of the light-matter interaction in a charge-ordered molecular insulator alpha-(BEDT-TTF)(2)I(3) were studied by pump-probe spectroscopy using few-optical-cycle infrared pulses (pulse width 12 fs). Coherent oscillation of the correlated electrons and subsequent Fano destructive interference with intramolecular vibration were observed in time domain; the results indicated a crucial role for electron-electron interplay in the light-matter interaction leading to the photoinduced insulator-to-metal transition. The qualitative features of this correlated electron motion were reproduced by calculations based on exact many-electron-phonon wave functions.

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  • Photoinduced coherent oscillations in the one-dimensional two-orbital Hubbard model Reviewed

    N. Maeshima, K. Hino, K. Yonemitsu

    Physical Review B - Condensed Matter and Materials Physics   82 ( 16 )   161105(R) (4 pages)   2010.10

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    We study photoinduced ultrafast coherent oscillations originating from orbital degrees of freedom in the one-dimensional two-orbital Hubbard model. By solving the time-dependent Schrödinger equation for the numerically exact many-electron wave function, we obtain time-dependent optical response functions. The calculated spectra show characteristic coherent oscillations that vary with the frequency of probe light. A simple analysis for the dominant oscillating components clarifies that these photoinduced oscillations are caused by the quantum interference between photogenerated states. The oscillation attributed to the Raman-active orbital excitations (orbitons) clearly appears around the charge-transfer peak. © 2010 The American Physical Society.

    DOI: 10.1103/PhysRevB.82.161105

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  • 24aRE-9 Photoinduced Dynamics in a Dimer-Mott Phase : Modulation of Interactions vs. Introduction of Carriers

    Yonemitsu,Kenji, Miyashita,Satoshi, Maeshima,Nobuya

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   693   2010.8

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  • 24aRE-4 The effect of the electron-lattice interaction on charge dynamics in one-dimensional Mott insulators

    Uemura,H, Maeshima,N, Yonemitsu,K, Okamoto,H

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   692   2010.8

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  • Frustration and lattice effects on photoinduced melting of charge orders in quasi-two-dimensional organic conductors Reviewed

    Kenji Yonemitsu, Satoshi Miyashita, Yasuhiro Tanaka

    PHYSICA B-CONDENSED MATTER   405 ( 11 )   S369 - S372   2010.6

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    Quasi-two-dimensional organic conductors theta-(BEDT-TTF)(2)RbZn(SCN)(4) and alpha-(BEDT-TTF)(2)I-3 [BED-TTF- bis(ethylenedithio)tetrathiafulvalene] are known to have quite similar charge-ordered ground states with so-called horizontal stripes Their photoinduced dynamics toward conductive states are quite different and their mechanisms are theoretically studied by numerical solutions to the time-dependent Schrodinger equation for the exact many-electron wave functions coupled with classical phonons in extended Peierls-Hubbard models on anisotropic triangular lattices The theta-type salt has a highly symmetric crystal structure and its triangular lattice Induces charge frustration which is relieved by molecular rotations in the charge-ordered state The lattice effect is thus strong and the large lattice stabilization energy makes the charge order hard compared with that in the a- type salt The different structural symmetries are reflected in their photoinduced evolutions of ground-state populations and charge distributions (C) 2009 Elsevier B V All rights reserved

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  • Theory of I-V characteristics for two-dimensional charge-ordered electron systems at quarter filling Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    PHYSICA B-CONDENSED MATTER   405 ( 11 )   S211 - S213   2010.6

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    The current-voltage characteristics and charge distribution of charge-ordered electron systems at quarter-filling under an applied bias voltage (V) are investigated theoretically by using nonequilibrium Green s functions We consider an extended Hubbard model with long-range Coulomb interactions on a square lattice which describes a checkerboard-type charge order in the absence of the bias V The effects of metallic electrodes are incorporated Into the self-energy The electron density and a scalar potential that satisfies the Poisson equation with a suitable boundary condition are calculated self-consistently within the Hartree approximation A first-order transition is observed from the charge-ordered insulating state to a conductive state with increasing V In the former state the charge distribution is almost unchanged by V whereas the charge order disappears so that the charge distribution is basically uniform in the latter state (C) 2009 Elsevier B V All rights reserved

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  • 2軌道縮退ハバード模型における光誘起ダイナミクス(研究会「相関電子系における光誘起現象」報告,研究会報告)

    前島, 展也, 日野, 健一, 米満, 賢治

    Bussei Kenkyu   94 ( 2 )   219 - 219   2010.5

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  • 20aHK-1 Photoinduced dynamics in a multi-orbital Hubbard model

    Maeshima,Nobuya, Hino,Ken-ichi, Yonemitsu,Kenji

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   728 - 728   2010.3

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  • Charge, Lattice, and Spin Dynamics in Photoinduced Phase Transitions from Charge-Ordered Insulator to Metal in Quasi-Two-Dimensional Organic Conductors Reviewed

    Satoshi Miyashita, Yasuhiro Tanaka, Shinichiro Iwai, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   79 ( 3 )   034708 (9 pages)   2010.3

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    To elucidate the different photoinduced melting dynamics of charge orders observed in the quasi-two-dimensional organic conductors theta-(BEDT-TTF)(2)RbZn(SCN)(4) and alpha-(BEDT-TTF)(2)I-3 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene], we theoretically study the photoinduced time evolution of charge and spin correlation functions on the basis of exact many-electron wave functions coupled with classical phonons in extended Peierls-Hubbard models on anisotropic triangular lattices. In both salts, the so-called horizontal-stripe charge order is stabilized by nearest-neighbor repulsive interactions and electron-lattice interactions. In theta-(BEDT-TTF)(2)RbZn(SCN)(4) (abbreviated as theta-RbZn), the stabilization energy due to lattice distortion is larger, so that a larger quantity of energy needs to be absorbed to melt charge and lattice orders. The photoinduced charge dynamics shows a complex behavior owing to a substantial number of nearly degenerate eigenstates involved. This is related to the high structural symmetry when the lattice is undistorted. In alpha-(BEDT-TTF)(2)I-3 (abbreviated as alpha-I-3), the lattice stabilization energy is smaller, and a small quantity of energy is sufficient to melt charge and lattice orders leading to a metallic phase. The photoinduced charge dynamics shows a sinusoidal oscillation. In alpha-I-3, the low structural symmetry ensures nearly spin-singlet bonds between hole-rich sites, where the spin correlation survives even after photoexcitation.

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  • Growth Dynamics of Photoinduced Domains in Two-Dimensional Charge-Ordered Conductors Depending on Stabilization Mechanisms Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   79 ( 2 )   024712 (8 pages)   2010.2

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    Photoinduced melting, of horizontal-stripe charge orders in quasi-two-dimensional organic conductors theta-(BEDT-TTF)(2)RbZn(SCN)(4) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] and alpha-(BEDT-TTF)(2)I-3 is investigated theoretically. By numerically solving the time-dependent Schrodinger equation, we study the photoinduced dynamics in extended Peierls-Hubbard models on anisotropic triangular lattices within the Hartree-Fock approximation. The inching of the charge order needs more energy for theta-(BEDT-TTF)(2)RbZn(SCN)(4) than for alpha-(BEDT-TTF)(2)I-3, which is a consequence of the larger stabilization energy in theta-(BEDT-TTF)(2)RbZn(SCN)(4). After local photoexcitation in the charge ordered states, the growth of a photoinduced domain shows anisotropy. In theta-(BEDT-TTF)(2)RbZn(SCN)(4), the domain hardly expands to the direction perpendicular to the horizontal-stripes. This is because all the molecules on the hole-rich stripe are rotated in one direction and those on the hole-poor stripe in the other direction. They Modulate horizontally connected transfer integrals homogeneously, stabilizing the charge order stripe by stripe. In alpha-(BEDT-TTF)(2)I-3, lattice distortions locally stabilize the charge order so that it is easily weakened by local photoexcitation. The photoinduced domain indeed expands in the plane. These results are consistent with recent observation by femtosecond reflection spectroscopy.

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  • Photoinduced dynamics in the one-dimensional two-orbital degenerate Hubbard model Reviewed

    Nobuya Maeshima, Kenji Yonemitsu, Ken-ichi Hino

    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009)   200   012109 (4 pages)   2010

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    We study photoinduced dynamical properties of the one-dimensional two-orbital degenerate Hubbard model. By using the Lanczos diagonalization method, we calculate optical conductivity spectra of the lowest photoexcited state. The optical conductivity has the Drude-like low-energy component caused by photogenerated carriers, a holon and a triplet doublon. We have also found an additional low-energy component in the spectra, which demonstrates a transition from the triplet doublon to singlet doublons.

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  • 26aXB-11 Photoinduced dynamics in a two-orbital degenerate Hubbard mode

    Maeshima,Nobuya, Hino,Ken-ichi, Yonemitsu,Kenji

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   634   2009.8

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  • Nonequilibrium Green's-Function Approach to the Suppression of Rectification at Metal-Mott-Insulator Interfaces Reviewed

    Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 5 )   054705 (8 pages)   2009.5

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    The suppression of rectification at metal-Mott-insulator interfaces, which was previously shown by numerical solutions to the time-dependent Schrodinger equation and experiments on real devices, is reinvestigated theoretically using nonequilibrium Green's functions. The one-dimensional Hubbard model is used for a Mott insulator. The effects of attached metallic electrodes are incorporated into the self-energy. A scalar potential originating from work-function differences and satisfying the Poisson equation is added to the model. For electron density, we decompose it into three parts. One is obtained by integrating the local density of states over energy to the midpoint of the electrodes' chemical potentials. The others, obtained by integrating lesser Green's functions, are due to couplings with the electrodes and correspond to an inflow and an outflow of electrons. In Mott insulators, incoming electrons and holes are extended over the whole system, avoiding further accumulation of charges relative to that in the case without bias. This induces collective charge transport and results in the suppression of rectification.

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  • Coupling-dependent rate of energy transfer from photoexcited Mott insulators to lattice vibrations Reviewed

    Kenji Yonemitsu, Nobuya Maeshima

    Physical Review B - Condensed Matter and Materials Physics   79 ( 12 )   125118 (6 pages)   2009.3

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    Photoexcited states are relaxed by transferring energy to the environments. In order to study which coupling allows fast energy transfer to lattice vibrations in correlated electron systems, we calculate the time evolutions of the kinetic energies of different types and frequencies of lattice vibrations. The one-dimensional half-filled Hubbard model is augmented with electron-lattice couplings that modulate transfer integrals, site energies, and Coulomb repulsion strengths. The time-dependent Schrödinger equation is solved for exact many-electron wave functions, and the classical equation of motion for the lattice displacements. In order to transfer energy to classical lattice vibrations that modulate transfer integrals or site energies, the translational invariance must be broken to give optical activity to an electronic excitation with wave number π and to these lattice vibrations. On the other hand, a certain amount of energy is always transferred to lattice vibrations that modulate Coulomb repulsion strengths, irrespective of the symmetry of the ground state, as long as the corresponding electron-lattice couplings are present. In strongly correlated electron systems, these couplings can be strong, although they are usually insignificant because their effects on the equilibrium properties can be absorbed into redefinition of Coulomb repulsion strengths. We will discuss competition or collaboration between energy-transfer pathways through different types of electron-lattice couplings. © 2009 The American Physical Society.

    DOI: 10.1103/PhysRevB.79.125118

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  • Erratum to Two papers on charge order with structural distortion in organic conductors (Journal of the Physical Society of Japan (2008) 77, (034708)) Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    Journal of the Physical Society of Japan   78 ( 1 )   2009.1

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    DOI: 10.1143/JPSJ.78.018002

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  • Energy transfer to phonons after photoexcitation in one-dimensional correlated electron-phonon systems Reviewed

    Kenji Yonemitsu, Nobuya Maeshima

    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 1   6 ( 1 )   240 - +   2009

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    In order to study relaxation rates of photoexcited states in correlated electron systems, we calculate the time evolution of phonons' kinetic energies after photoexcitation of a one-dimensional half-filled Hubbard model coupled with different types of phonons, which modulate transfer integrals, site energies, and on-site repulsion strengths. Without or with weak dimerization, the energy transfer to phonons that modulate on-site repulsion strengths is the largest. It increases rapidly as a function of the corresponding displacement. This suggests that the rapid relaxation of photoexcited states in one-dimensional correlated electron systems is allowed without change in symmetry by phonons that modulate Coulomb repulsion strengths. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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  • Effects of spin fluctuations, charge fluctuations and lattice distortions on charge orders in theta- and alpha-type BEDT-TTF salts Reviewed

    Satoshi Miyashita, Kenji Yonemitsu

    LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3)   148   012006 (3 pages)   2009

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    Effects of spin fluctuations, charge fluctuations and lattice distortions on charge orders in theta-(BEDT-TTF)(2)RbZn(SCN)(4) and alpha-(BEDT-TTF)(2)I-3 axe investigated theoretically in a two-dimensional extended Peierls-Hubbaxd model. By using exact diagonalization, we have calculated hole-density distributions and transfer modulations with transfer integrals based on the corresponding high-temperature structures as a function of electron-phonon couplings. The results clearly show the origin of their lattice-effect differences, namely, the lattice effect on theta-(BEDT-TTF)(2)RbZn(SCN)(4) is much larger than that on alpha-(BEDT-TTF)(2)I-3. This finding is systematically explained by the strong-coupling perturbation theory. It is found that spin fluctuations induce lattice distortions in theta-(BEDT-TTF)(2)RbZn(SCN)(4), but their effects axe partially cancelled by charge fluctuations in alpha-(BEDT-TTF)(2)I-3.

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  • Photoinduced melting and charge order in quarter-filled organic conductors: Itinerant electron systems with competing interactions Reviewed

    Kenji Yonemitsu, Nobuya Maeshima, Yasuhiro Tanaka, Satoshi Miyashita

    LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3)   148   012054 (5 pages)   2009

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    Photoinduced charge dynamics in one- and two-dimensional organic conductors are studied theoretically in extended Peierls-Hubbard models. For quasi-one-dimensional (EDO-TTF)(2)PF6, photoinduced change in the charge order pattern from (0110) to (1010) is accompanied by probe-energy-dependent oscillations of conductivity. This is caused by coexistence of charge order and delocalized electrons. For quasi-two-dimensional alpha-(BEDT-TTF)(2)I-3 and theta-(BEDT-TTF)(2)RbZn(SCN)(4), photoinduced melting of the horizontal-stripe charge order proceeds easier in the a-type salt than in the theta-type salt. This is because the charge order in the theta-type salt is more strongly stabilized by electron-phonon interactions.

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  • Role of electron-lattice couplings on charge order in quasi-two-dimensional organic conductors Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4   150 ( 4 )   042204 (4 pages)   2009

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    Charge ordering with structural distortion in quasi-two-dimensional organic conductors theta-(ET)(2)RbZn(SCN)(4) (ET=BEDT-TTF) and alpha-(ET)(2)I(3) is investigated for an extended Hubbard model with Peierls-type electron-lattice interactions within the Hartree-Fock approximation. It is found that the lattice effects stabilize the experimentally observed charge order substantially in theta-(ET)(2)RbZn(SCN)(4), whereas the energy gain by a lattice distortion is small and its band structure and Coulomb interactions play an important role to realize the charge order in alpha-(ET)(2)I(3). The results are consistent with experimental observations and show contrastive roles of lattice degrees of freedom on charge orders in these compounds.

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  • Photoinduced melting of charge order in quasi-two-dimensional organic conductors Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3)   148   012063 (3 pages)   2009

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    Photoinduced melting of charge order in quasi-two-dimensional organic conductors alpha-(ET)(2)I-3 (ET=BEDT-TTF) and theta-(ET)(2)RbZn(SCN)(4) is investigated theoretically. By solving the time-dependent Schrodinger equation numerically within the Haxtree-Fock approximation for an extended Peierls-Hubbaxd model, we study the photoinduced dynamics in each compound. The obtained charge, spin and lattice dynamics are considered to reflect the different natures of charge ordered states in these systems. In particular, the melting of charge order needs more energy for theta-(ET)(2)RbZn(SCN)(4) than for alpha-(ET)(2)I-3, which is a consequence of large lattice distortion and the essential role of electron-phonon coupling in stabilizing the charge order in theta-(ET)(2)RbZn(SCN)(4).

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  • Mott insulating state in a quarter-filled two-orbital Hubbard chain with different bandwidths Reviewed

    Satoshi Miyashita, Yasufumi Yamashita, Kenji Yonemitsu, Akihisa Koga, Norio Kawakami

    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4   150 ( 4 )   042128 (4 pages)   2009

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    We investigate the ground-state properties of the one-dimensional two-band Hubbard model with different bandwidths. The density-matrix renormalization group method is applied to calculate the averaged electron occupancies n as a function of the chemical potential mu. Both at quarter and half fillings, "charge plateaux" appear in the n-mu plot, where d mu/dn diverges and the Mott insulating states are realized. To see how the orbital polarization in the one-quarter charge plateau develops, we apply the second-order perturbation theory from the strong-coupling limit at quarter filling. The resultant Kugel-Khomskii spin-orbital model includes a magnetic field coupled to orbital pseudo-spins. This field originates from the discrepancy between the two bandwidths and leads to a finite orbital pseudo-spin magnetization.

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  • Photogenerated polaronic state in a one-dimensional dimerized Mott insulator K-TCNQ Reviewed

    Nobuya Maeshima, Kenji Yonemitsu, Ken-ichi Hino

    LXIII YAMADA CONFERENCE ON PHOTO-INDUCED PHASE TRANSITION AND COOPERATIVE PHENOMENA (PIPT3)   148   012005 (4 pages)   2009

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    We discuss photogenerated midgap states of a one-dimensional dimerized Mott insulator potassium-tetracyanoquinodimetbane (K-TCNQ). We take account of two types of phonons, the intermolecular and the intramolecular vibrations. We treat these phonon modes adiabatically and analyse a theoretical model by using the density matrix renormalization group (DMRG). Our numerical results demonstrate that the midgap state of K-TCNQ can be reproduced by the intermolecular lattice distortion.

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  • Enhanced coherent dynamics near a transition between neutral quantum-paraelectric and ionic ferroelectric phases in the quantum Blume-Emery-Griffiths model Reviewed

    Kenji Yonemitsu

    PHYSICAL REVIEW B   78 ( 20 )   205102 (5 pages)   2008.11

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    Nonequilibrium dynamics is studied near the quantum phase transition point in the one-dimensional quantum Blume-Emery-Griffiths model. Its pseudospin component S-z represents an electric polarization, and (S-z)(2) corresponds to ionicity, in mixed-stack charge-transfer complexes that exhibit a transition between neutral quantum-paraelectric and ionic ferroelectric (or antiferroelectric) phases. The time-dependent Schrodinger equation is solved for the exact many-body wave function in the quantum-paraelectric phase. After impact force is introduced on a polarization locally in space and time, polarizations and ionicity coherently oscillate. The oscillation amplitudes are large near the quantum phase transition point. The energy supplied by the impact flows linearly into these oscillations, so that the nonequilibrium behavior is uncooperative.

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  • Modified Barrett formula near the neutral-ionic quantum phase transition Reviewed

    Y. Yamashita, K. Yonemitsu

    Journal of Physics: Conference Series   132   012019 (5 pages)   2008.10

  • Spin and charge fluctuations and lattice effects on charge ordering in alpha-(BEDT-TTF)(2)I-3 Reviewed

    Satoshi Miyashita, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   77 ( 9 )   094712 (6 pages)   2008.9

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    The effects of spin and charge fluctuations and electron-phonon couplings on charge ordering in alpha(BEDT-TTF)(2)I-3 [BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalence] are investigated theoretically for all anisotropic triangular lattice at 3/4 filling. By the exact-diagonalization method. we have calculated the hole density distributions and the modulations of transfer integrals from high-temperature values as it function of electron-phonon coupling strength. The results clearly show that the lattice effect on alpha-(BEDT-TTF)(2)I-3 is weak compared with that on theta-(BEDT-TTF)(2)RbZn(SCN)(4) as previously found by experiments. This finding. which is also consistent with recent mean-field results, is systematically explained by strong-coupling perturbation theory: the effects of spin fluctuations tire partially canceled by charge fluctuations in alpha-(BEDT-TTF)(2)I-3.

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  • Photoinduced change in the charge order pattern in the quarter-filled organic conductor (EDO-TTF)(2)PF6 with a strong electron-phonon interaction Reviewed

    Ken Onda, Sho Ogihara, Kenji Yonemitsu, Nobuya Maeshima, Tadahiko Ishikawa, Yoichi Okimoto, Xiangfeng Shao, Yoshiaki Nakano, Hideki Yamochi, Gunzi Saito, Shin-ya Koshihara

    PHYSICAL REVIEW LETTERS   101 ( 6 )   067403 (4 pages)   2008.8

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    The quasistable state in the photoinduced phase transition for the quasi-one-dimensional quarter-filled organic conductor (EDO-TTF)(2)PF6 has been examined by ultrafast reflective measurements and time-dependent model calculations incorporating both electron-electron and electron-phonon interactions. The transient optical conductivity spectrum over a wide probe photon-energy range revealed that photoexcitation induced a new type of charge-disproportionate state. Additionally, coherent and incoherent oscillations dependent on probe photon energies were found, as predicted by the calculation.

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  • Theory of photoinduced phase transitions in itinerant electron systems Reviewed

    Kenji Yonemitsu, Keiichiro Nasu

    PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS   465 ( 1 )   1 - 60   2008.8

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    Theoretical progress in the research of photoinduced phase transitions is reviewed with closely related experiments. After a brief introduction of stochastic evolution in statistical systems and domino effects in localized electron systems, we treat photoinduced dynamics in itinerant-electron systems. Relevant interactions are required in the models to describe the fast and ultrafast charge-lattice-coup led dynamics after photoexcitations. First, we discuss neutral-ionic transitions in the mixed-stack charge-transfer complex. TTF-CA. When induced by intrachain charge-transfer photoexcitations, the dynamics of the ionic-to-neutral transition are characterized by a threshold behavior, while those of the neutral-to-ionic transition by an almost linear behavior. The difference originates from the different electron correlations in the neutral and ionic phases. Second, we deal with halogen-bridged metal complexes, which show metal, Mott insulator, charge-density-wave, and charge-polarization phases. The latter two phases have different broken symmetries. The charge-density-wave to charge-polarization transition is much more easily achieved than the reverse transition. This is clarified by considering microscopic charge-transfer processes. The transition from the charge-density-wave to Mott insulator phases and that from the Mott insulator to metal phases proceed much faster than those between the low-symmetry phases. Next, we discuss ultrafast, inverse spin-Peierls transitions in an organic radical crystal and alkali-TCNQ from the viewpoint of intradimer and interdimer charge-transfer excitations. Then, we study photogenerated electrons in the quantum paraelectric perovskite, SrTiO3, which are assumed to couple differently with soft-anharmonic phonons and breathing-type high-energy phonons. The different electron-phonon couplings result in two types of polarons, a "super-paraelectric large polaron" with a quasi-global parity violation, and an "off-center-type self-trapped polaron" with only a local parity violation. The former is equivalent to a charged and conductive ferroelectric domain, which greatly enhances both the quasi-static electric susceptibility and the electric conductivity. Finally, we outline the development of time-resolved X-ray diffraction experiments, which directly accesses the dynamics of electronic, atomic and molecular motions in photoexcited materials. They are extremely useful when a three-dimensional structural long-range order is established and changes the symmetry. (C) 2008 Elsevier B.V. All rights reserved.

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  • Polaronic states with spin-charge-coupled excitation in a one-dimensional dimerized Mott insulator K-TCNQ Reviewed

    Nobuya Maeshima, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   77 ( 7 )   074713 (6 pages)   2008.7

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    We discuss photogenerated midgap states of a one-dimensional (1D) dimerized Mott insulator, potassium-tetracyanoquinodimethane (K-TCNQ). Two types of phonon modes are taken into account: intermolecular and intramolecular vibrations. We treat these phonon modes adiabatically and analyze a theoretical model by using the density-matrix renormalization group (DMRG). Our numerical results demonstrate that the intermolecular lattice distortion is necessary to reproduce the photoinduced midgap absorption in K-TCNQ. We find two types of midgap states. One is a usual polaronic state characterized by a localized elementary excitation. The other is superposition of two types of excitations, a doped-carrier state and a triplet-dimer state, which can be generally observed in 1D dimerized Mott insulators, not limited to K-TCNQ.

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  • Theory of Photoinduced Phase Transitions : Coherent Oscillations and Transient States

    YONEMITSU Kenji

    rle   36 ( 6 )   343 - 348   2008.6

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    Theoretical understanding of photoinduced phase transitions and their dynamics is reviewed from the viewpoint of coherent oscillations and transient states in condensed molecular materials with quasi-one-dimensional electronic conduction. In the mixed-stack organic charge-transfer compound TTF-CA (TTF: tetrathiafulvalene, CA: chloranil), the photoinduced transition from the ionic phase to the neutral phase is accompanied with coherent motion of a neutral-ionic domain boundary. Its high cooperativity is realized by the sufficiently strong, interchain Coulomb coupling in the ionic phase. In the quarter-filled-band organic salt (EDO-TTF) 2PF6 (EDO: ethylenedioxy), the photoinduced melting of charge order is accompanied with oscillations in transient reflectivity. The degree of coherence in these oscillations depends on the probe photon energy. It is caused by different space and time scales of observed electronic motion and relevant phonon motion.

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  • Charge order with structural distortion in organic conductors: Comparison between theta-(ET)(2)RbZn(SCN)(4) and alpha-(ET)(2)I-3 Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   77 ( 3 )   034708 (9 pages)   2008.3

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    Charge ordering with structural distortion in quasi-two-dimensional organic conductors theta-(ET)(2)RbZn(SCN)(4) (ET = BEDT-TTF) and alpha-(ET)(2)I-3 is investigated theoretically. By using the Hartree-Fock approximation for an extended Hubbard model which includes both on-site and intersite Coulomb interactions together with Peierls-type electron-lattice couplings, we examine the role of lattice degrees of freedom on charge order. It is found that the experimentally observed, horizontal charge order is stabilized by lattice distortion in both compounds. In particular, the lattice effect is crucial to the realization of the charge order in theta-(ET)(2)RbZn(SCN)(4), while the peculiar band structure whose symmetry is lower than that of theta-(ET)(2)RbZn(SCN)(4) in the metallic phase is also an important factor in alpha(ET)(2)I-3 together with the lattice distortion. For alpha-(ET)(2)I-3, we obtain a phase transition from a charge-disproportionated metallic phase to the horizontal charge order with lattice modulations, which is consistent with the latest X-ray experimental result.

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  • Suppression of rectification at metal-Mott insulator interfaces Reviewed

    Kenji Yonemitsu, Nobuya Maeshima, Tatsuo Hasegawa

    PHYSICAL REVIEW B   76 ( 23 )   235118 (6 pages)   2007.12

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    Charge transport through metal-Mott insulator interfaces is studied and compared with that through metal-band-insulator interfaces. For band insulators, rectification has been known to occur owing to a Schottky barrier, which is produced by the work-function difference. For Mott insulators, however, qualitatively different current-voltage characteristics are obtained. Theoretically, we use the one-dimensional Hubbard model for a Mott insulator and attach to it the tight-binding model for metallic electrodes. A Schottky barrier is introduced by a solution to the Poisson equation with a simplified density-potential relation. The current density is calculated by solving the time-dependent Schrodinger equation. We mainly use the time-dependent Hartree-Fock approximation and also use exact many-electron wave functions on small systems for comparison. Rectification is found to be strongly suppressed even for large work-function differences. We show its close relationship with the fact that field-effect injections into one-dimensional Mott insulators are ambipolar. Experimentally, we fabricated asymmetric contacts on top of single crystals of quasi-one-dimensional organic Mott and band insulators. Rectification is strongly suppressed at an interface between metallic magnesium and Mott-insulating (BEDT-TTF)(F(2)TCNQ) [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene; F(2)TCNQ=2,5-difluorotetracyanoquinodimethane].

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  • Photoinduced melting of charge order in a quarter-filled electron system coupled with different types of phonons Reviewed

    Kenji Yonemitsu, Nobuya Maeshima

    PHYSICAL REVIEW B   76 ( 7 )   075105 (6 pages)   2007.8

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    Photoinduced melting of charge order is calculated by using the exact many-electron wave function coupled with classically treated phonons in the one-dimensional quarter-filled Hubbard model with Peierls and Holstein types of electron-phonon couplings. The model parameters are taken from recent experiments on (EDO-TTF)(2)PF6 (EDO-TTF=ethylenedioxy-tetrathiafulvalene) with a (0110) charge order, where transfer integrals are modulated by molecular displacements (bond-coupled phonons) and site energies by molecular deformations (charge-coupled phonons). The charge-transfer photoexcitation from (0110) to (0200) configurations and that from (0110) to (1010) configurations have different energies. The corresponding excited states have different shapes of adiabatic potentials as a function of these two phonon amplitudes. The adiabatic potentials are shown to be useful in understanding differences in the photoinduced charge dynamics and the efficiency of melting, which depend not only on the excitation energy but also on the relative phonon frequency of the bond- and charge-coupled phonons.

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  • Charge-transfer excitations in one-dimensional dimerized mott insulators Reviewed

    Nobuya Maeshima, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76 ( 7 )   074713 (5 pages)   2007.7

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    We investigate the optical properties of one-dimensional (1D) dimerized Mott insulators using the 1D dimerized extended Hubbard model. Numerical calculations and a perturbative analysis from the decoupled-dimer limit clarify that there are three relevant classes of charge-transfer (CT) states generated by photoexcitation: interdimer CT unbound states, interdimer CT exciton states, and intradimer CT exciton states. This classification is applied to understanding the optical properties of an organic molecular material, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), which is known for its photoinduced transition from the dimerized spin-singlet phase to the regular paramagnetic phase. We conclude that the lowest photoexcited state of TTTA is the interdimer CT exciton state and the second lowest state is the intradimer CT exciton state.

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  • Relaxation process in the photoinduced neutral-ionic paraelectric-ferroelectric phase transition in tetrathiafulvalene-p-chloranil Reviewed

    Hitoshi Inoue, Kenji Yonemitsu

    PHYSICAL REVIEW B   75 ( 23 )   235125 (13 pages)   2007.6

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    To find characteristic properties of relaxation process in the neutral-ionic, paraelectric-ferroelectric phase transition in the charge-transfer complex, tetrathiafulvalene-p-chloranil, we investigate stochastic process in the spin 1 anisotropic Blume-Emery-Griffith model [Phys. Rev. A 4, 1071 (1971)]. We assume that spins obey the Markov process which is described by the master equation with the transfer probability 1/tau exp[-(beta/2)Delta H], where Delta H is the energy difference for the transfer. We derive time-evolution equations from two standpoints. One is the mean-field approximation (MFA) and the other is an extension of the Saito-Kubo treatment to the spin 1 and anisotropic case, which improves MFA. Solving the equations numerically, we have found highly anisotropic relaxations during the neutral-ionic phase transition: the interchain ordering develops much more slowly than the intrachain one. In contrast, the ionic-neutral phase transition proceeds rather isotropically.

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  • Charge ordering in theta-(BEDT-TTF)(2)RbZn(SCN)(4): Cooperative effects of electron correlations and lattice distortions Reviewed

    Satoshi Miyashita, Kenji Yonemitsu

    PHYSICAL REVIEW B   75 ( 24 )   245112 (6 pages)   2007.6

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    Combined effects of electron correlations and lattice distortions on the charge ordering in theta-(BEDT-TTF)(2)RbZn(SCN)(4) are investigated theoretically in a two-dimensional 3/4-filled extended Hubbard model with electron-lattice couplings. It is known that this material undergoes a phase transition from a high-symmetry metallic state to a low-symmetry insulating state with a horizontal-stripe charge order (CO) by lowering temperature. By means of the exact-diagonalization method, we show that electron-phonon interactions are crucial to stabilize the horizontal-stripe CO and to realize the low-symmetry crystal structure.

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  • Effects of electron-lattice coupling on charge order in θ-(ET) 2X Reviewed

    Yasuhiro Tanaka, Kenji Yonemitsu

    Journal of the Physical Society of Japan   76 ( 5 )   053708 (5 pages)   2007.5

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    Charge ordering accompanied by lattice distortion in quasi-two dimensional organic conductors θ-(ET) 2X (ET = BEDT-TTF) is studied by using an extended Hubbard model with Peierls-type electron-lattice couplings within the Hartree-Fock approximation. It is found that the horizontal-stripe charge-ordered state, which is experimentally observed in θ-(ET) 2RbZn(SCN) 4, is stabilized by the self-consistently determined lattice distortion. Furthermore, in the presence of the anisotropy in nearest-neighbor Coulomb interactions V ij, the horizontal charge order becomes more stable than any other charge patterns such as diagonal, vertical and 3-fold-type states. At finite temperatures, we compare the free energies of various charge-ordered states and find a first-order transition from a metallic state with 3-fold charge order to the insulating state with the horizontal charge order. The role of lattice degrees of freedom in the realization of the horizontal charge order and the relevance to experiments on θ-(ET) 2X are discussed. ©2007 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.76.053708

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  • Possibility of field-induced incommensurate order in a quasi-one-dimensional frustrated spin system Reviewed

    N Maeshima, K Okunishi, K Okamoto, T Sakai, K Yonemitsu

    JOURNAL OF PHYSICS-CONDENSED MATTER   18 ( 20 )   4819 - 4826   2006.5

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    We study an incommensurate long-range order induced by an external magnetic field in a quasi-one-dimensional bond-alternating spin system, F5PNN, focusing on the role of the frustrating interaction which can be enhanced by a high-pressure effect. On the basis of the density matrix renormalization group analysis of a microscopic model for F5PNN, we present several H-T phase diagrams for typical parameters of the frustrating next-nearest-neighbour coupling and the interchain interaction, and then discuss how the field-induced incommensurate order develops by the frustration effect in such phase diagrams. A magnetization plateau at half the saturation moment is also mentioned.

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  • Phase diagram of the excitonic insulator Reviewed

    B Hulsen, FX Bronold, H Fehske, K Yonemitsu

    PHYSICA B-CONDENSED MATTER   378-80   267 - 268   2006.5

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    Motivated by recent experiments, which give strong evidence for an excitonic insulating phase in TmSe0.45Te0.55, we developed a scheme to quantitatively construct, for generic two-band models, the phase diagram of an excitonic insulator. As a first application of our approach, we calculated the phase diagram for an effective mass two-band model with long-range Coulomb interaction. The shielded potential approximation is used to derive a generalized gap equation controlling for positive (negative) energy gaps the transition from a semi-conducting (semi-metallic) phase to an insulating phase. Numerical results. obtained within the quasi-static approximation, show a steeple-like phase diagram in contrast to long-standing expectations. (c) 2006 Elsevier B.V. All rights reserved.

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  • Interchain coupling effects on photoinduced phase transitions between neutral and ionic phases in an extended Hubbard model with alternating potentials and an electron-lattice coupling Reviewed

    K Yonemitsu

    PHYSICAL REVIEW B   73 ( 15 )   155120 (7 pages)   2006.4

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    Dynamics of ionic-to-neutral and neutral-to-ionic phase transitions induced by intrachain charge-transfer photoexcitations are studied in a quasi-one-dimensional extended Hubbard model with alternating potentials and an electron-lattice coupling for mixed-stack charge-transfer complexes. For interchain couplings, we use electron-electron interactions previously estimated for TTF-CA (TTF=tetrathiafulvalene, CA=chloranil). Photoexcitation is introduced by a pulse of oscillating electric field. The time-dependent Hartree-Fock (HF) approximation is used for the electronic part, and the classical approximation for the lattice part. In the ionic-to-neutral transition, the transferred charge density is a strongly nonlinear function of the photoexcitation density, which is characterized by the presence of a threshold. With substantial interchain couplings comparable to those in TTF-CA, the interchain correlation is strong during the transition. Neutral domains in nearby chains simultaneously grow even if their nucleation is delayed by reducing the amplitude of the electric field. With weaker interchain couplings, the growing processes are in phase only when the amplitude of the electric field is large. Thus, the experimentally observed, coherent motion of a macroscopic neutral-ionic domain boundary is allowed to emerge by such substantial interchain couplings. In the neutral-to-ionic transition, by contrast, the transferred charge density is almost a linear function of the photoexcitation density. Interchain electron-electron interactions make the function slightly nonlinear, but the uncooperative situation is almost unchanged and consistent with the experimental findings.

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  • Interchain-coupling effects on photoinduced neutral-ionic transition dynamics in mixed-stack charge-transfer complexes Reviewed

    K. Yonemitsu

    JOURNAL OF LOW TEMPERATURE PHYSICS   142 ( 3-4 )   499 - 502   2006.2

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    Effects of interchain electron-electron interactions on the photoinduced ionic-to-neutral and neutral-to-ionic transition dynamics are studied in a quasi-one-dimensional extended Peierls-Hubbard model with alternating potentials for mixed-stack charge-transfer complexes. The ionic-to-neutral transition dynamics depend on the strengths of interchain couplings. For weak couplings, the interchain coherence is destroyed For strong couplings such as those corresponding to TTF-CA, once neutral domains are nucleated above an increased absorption threshold, they grow spontaneously and cooperatively till the whole system is converted In contrast, interchain couplings slightly enhance nonlinearity of the otherwise uncooperative neutral-to-ionic transition dynamics.

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  • Theory of photoinduced phase transitions Reviewed

    K Yonemitsu, K Nasu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75 ( 1 )   011008 (8 pages)   2006.1

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    Theories of photoinduced phase transitions have developed along with the progress in experimental studies, especially concerning their nonlinear characters and transition dynamics. At an early stage, paths from photoinduced local structural distortions to global ones are explained in classical statistical models. Their dynamics are governed by transition probabilities and inevitably stochastic, but they were sufficient to describe coarse-grained time evolutions. Recently, however, a variety of dynamics including ultrafast ones are observed in different electronic states. They are explained in relevant electronic models. In particular, a coherent lattice vibration and coherent motion of a macroscopic domain boundary need appropriate interactions among electrons and lattice displacements. Furthermore, some transitions proceed almost in one direction, which can be explained by considering relevant electronic processes. We describe the history of theories of photoinduced phase transitions and discuss a future perspective.

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  • Dynamics of photoexcited states in one-dimensional dimerized Mott insulators Reviewed

    Nobuya Maeshima, Kenji Yonemitsu

    Physical Review B - Condensed Matter and Materials Physics   74 ( 15 )   155105 (11 pages)   2006

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    Dynamical properties of photoexcited states are theoretically studied in a one-dimensional Mott insulator dimerized by the spin-Peierls instability. Numerical calculations combined with a perturbative analysis have revealed that the lowest photoexcited state without nearest-neighbor interaction corresponds to an interdimer charge transfer excitation that belongs to dispersive excitations. This excited state destabilizes the dimerized phase, leading to a photoinduced inverse spin-Peierls transition. We discuss the purely electronic origin of midgap states that are observed in a latest photoexcitation experiment of an organic spin-Peierls compound, K-TCNQ (potassium- tetracyanoquinodimethane). © 2006 The American Physical Society.

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  • Photoinduced metallic properties of one-dimensional strongly correlated electron systems Reviewed

    N Maeshima, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 10 )   2671 - 2674   2005.10

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    We study photoinduced optical responses of one-dimensional strongly correlated electron systems. Optical conductivity spectra are calculated for the around and photoexcited states in a one-dimensional Hubbard model at half filling by the exact diagonalization method. It is found that, in the Mott insulator phase, the photoexcited state has large spectral weights including the Drude weight below the optical gap. As a consequence, the spectral weight above the optical gap is markedly reduced. These results imply that a metallic state is induced by photoexcitation. A comparison between the photoexcited and hole-doped states shows that photoexcitation is similar to chemical doping.

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  • Inter-chain Coulomb-lattice relaxation and multicriticality in charge transfer organic complexes Reviewed

    J Kishine, T Ohara, T Luty, K Yonemitsu

    SYNTHETIC METALS   154 ( 1-3 )   257 - 260   2005.9

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    We discuss the neutral-to-ionic phase transition and emergence of the multi-criticality in the quasi-one-dimensional charge-transfer salt TTF-CA under pressure. We stress that subtle interplay of Coulomb and lattice processes may be quite sensitive to pressure. Emergence or disappearance of the multi-critical points in a series of charge-transfer salts are understood through this interplay. What's behind is coexistence and coupling of the non-symmetry-breaking and symmetry-breaking order parameters.

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  • Mechanism of ambipolar field-effect carrier injections in one-dimensional Mott insulators Reviewed

    K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 9 )   2544 - 2553   2005.9

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    To clarify the mechanism of recently reported, ambipolar carrier injections into quasi-one-dimensional Mott insulators on which field-effect transistors are fabricated, we employ the one-dimensional Hubbard model attached to a tight-binding model for source and drain electrodes. To take account of the formation of Schottky barriers, we add scalar and vector potentials, which satisfy the Poisson equation with boundary values depending on the drain voltage, the gate bias, and the work-function difference. The current-voltage characteristics are obtained by solving the time-dependent Schrodinger equation in the unrestricted Hartree-Fock approximation. Its validity is discussed with the help of the Lanczos method applied to small systems. We find generally ambipolar carrier injections in Mott insulators even if the work function of the crystal is quite different from that of the electrodes. They result from balancing the correlation effect with the barrier effect. For the gate-bias polarity with higher Schottky barriers, the correlation effect is weakened accordingly, owing to collective transport in the one-dimensional correlated electron systems.

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  • Theory of photoinduced phase dynamics in organic charge-transfer complexes Reviewed

    K Yonemitsu

    JOURNAL OF LUMINESCENCE   112 ( 1-4 )   279 - 282   2005.4

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    In the quasi-one-dimensional mixed-stack organic charge-transfer complex, TTF-CA, photoirradiation is known to trigger transitions between the neutral and ionic phases. Here we use a one-dimensional extended Peierls-Hubbard model with alternating potentials and calculate the mean-field dynamics of charge density coupled with that of lattice displacements. We show qualitative differences between the photoinduced ionic-to-neutral and neutral-to-ionic transitions, which are consistent with recent experimental findings. That is, the ionic-to-neutral transition proceeds cooperatively, characterized by threshold behavior, while the neutral-to-ionic transition proceeds uncooperatively, characterized by linear behavior. The threshold absorption in the former depends on the strength or the duration of the pulse. The coherence during the transition dynamics is also different between the two transitions. In the ionic-to-neutral transition, a clear interference effect is observed as a function of the interval when the pulse is spilt into two. (c) 2004 Elsevier B.V. All rights reserved.

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  • Field-Induced Phase Transitions and Long-Range Orders in the S=1/2 Spin Bond-Alternating Chain with Frustrating Interaction Reviewed

    Nobuya Maeshima, Kouichi Okunishi, Kiyomi Okamoto, Toru Sakai, Kenji Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74   63 - 66   2005

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    We study field-induced phase transitions and long-range orders in the S = 1/2 spin bond-alternating chain with frustrating interaction. By using the inter-chain mean field theory combined with the finite temperature density matrix renormalization group, we investigate properties of field-induced long-range orders and phase transitions. We find that the inter-chain interaction strongly affects the realized phases of this system.

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  • Photoinduced dynamics and nonequilibrium characteristics in quasi-one-dimensional electron systems: Mott insulators vs. band insulators Reviewed

    K Yonemitsu

    Second International Conference on Photo-Induced Phase Transitions: Cooperative, Nonlinear and Functional Properties   21   30 - 37   2005

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    Electron-electron interactions play an important role in nonequilibrium properties of molecular materials. First, we show differences between photoinduced ionic-to-neutral and neutral-to-ionic transitions in quasi-one-dimensional extended Peierls Hubbard models with alternating potentials. Cooperative dynamics lead to nonlinear ionicity in the former, while uncooperative dynamics lead to quite linear ionicity in the latter, as a function of the energy supplied from the oscillating electric field. Interchain electron-electron interactions bring about initial competition among metastable and stable domains in neighboring chains, slowing down the phase transition. Interchain elastic couplings are necessary to form a ferroelectric long-range order. Second, we show differences between field-effect characteristics of Mott insulators and those of band insulators in one-dimensional Hubbard models, to which tight-binding models are attached for metallic electrodes and scalar potentials are added for interfacial barriers. Ambipolar characteristics are found in the former, while unipolar characteristics generally appear in the latter. In the former, charge transport is cooperative so that the drain current is insensitive to the difference between the work function of the channel and that of the electrodes, and thus insensitive to the polarity of the gate bias.

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  • Optical responses of photoexcited states in the one-dimensional ionic Hubbard model Reviewed

    N Maeshima, K Yonemitsu

    SECOND INTERNATIONAL CONFERENCE ON PHOTO-INDUCED PHASE TRANSITIONS: COOPERATIVE, NONLINEAR AND FUNCTIONAL PROPERTIES   21   183 - 188   2005

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    Photoinduced optical responses are studied in the one-dimensional ionic Hubbard model with the nearest-neighbor repulsion V. For V=0, carriers introduced by photoirradiation move freely both in the Mott insulator phase and in the band insulator phase, giving rise to a Drude peak in the optical conductivity spectrum. The carriers in the Mott insulator phase remain conducting for 0 < V < 2t because their kinetic energy overcomes the binding energy. By contrast, the electrons and the holes in the band insulator phase are bound to form excitons for V > 0, which do not contribute to the charge transport unless the excitation energy allows them to be separated. The dependence of the Drude weight in the lowest-energy photoexcited state on V and the system size is investigated for both phases. Implications to experimental studies of halogen-bridged metal-complex chains are discussed.

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  • Quantum Ising model coupled with conducting electrons Reviewed

    Y Yamashita, K Yonemitsu

    Second International Conference on Photo-Induced Phase Transitions: Cooperative, Nonlinear and Functional Properties   21   232 - 236   2005

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    The effect of photo-doping on the quantum paraelectric SrTiO3 is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.

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  • Phase transition in a one-dimensional extended Peierls-Hubbard model with a pulse of oscillating electric field: I. Threshold behavior in ionic-to-neutral transition Reviewed

    K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 )   2868 - 2878   2004.10

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    Photoinduced dynamics of charge density and lattice displacements is calculated by solving the time-dependent Schrodinger equation for a one-dimensional extended Peierls-Hubbard model with alternating potentials for the mixed-stack organic charge-transfer complex, TTF-CA. A pulse of oscillating electric field is incorporated into the Peierls phase of the transfer integral. The frequency, the amplitude, and the duration of the pulse are varied to study the nonlinear and cooperative character of the photoinduced transition. When the dimerized ionic phase is photoexcited, the threshold behavior is clearly observed by plotting the final ionicity as a function of the increment of the total energy. Above the threshold photoexcitation, the electronic state reaches the neutral one with equidistant molecules after the electric field is turned off. The transition is initiated by nucleation of a metastable neutral domain, for which an electric field with frequency below the linear absorption peak is more effective than that at the peak. When the pulse is strong and short, the charge transfer takes place on the same time scale with the disappearance of dimerization. As the pulse becomes weak and long, the dimerization-induced polarization is disordered to restore the inversion symmetry on average before the charge transfer takes place to bring the system neutral. Thus, a paraelectric ionic phase is transiently realized by a weak electric field. It is shown that infrared light also induces the ionic-to-neutral transition, which is characterized by the threshold behavior.

    DOI: 10.1143/JPSJ.73.2868

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  • Phase transition in a one-dimensional extended Peierls-Hubbard model with a pulse of oscillating electric field: II. Linear behavior in neutral-to-ionic transition Reviewed

    K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 )   2879 - 2886   2004.10

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    Dynamics of charge density and lattice displacements after the neutral phase is photoexcited is studied by solving the time-dependent Schrodinger equation for a one-dimensional extended Peierls-Hubbard model with alternating potentials. In contrast to the ionic-to-neutral transition studied previously, the neutral-to-ionic transition proceeds in an uncooperative manner as far as the one-dimensional system is concerned. The final ionicity is a linear function of the increment of the total energy. After the electric field is turned off, the electronic state does not significantly change, roughly keeping the ionicity, even if the transition is not completed, because the ionic domains never proliferate. As a consequence, an electric field with frequency just at the linear absorption peak causes the neutral-to-ionic transition the most efficiently. These findings are consistent with the recent experiments on the mixed-stack organic charge-transfer complex, TTF-CA. We artificially modify or remove the electron-lattice coupling to discuss the origin of such differences between the two transitions.

    DOI: 10.1143/JPSJ.73.2879

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  • Phase transition in a one-dimensional extended Peierls-Hubbard model with a pulse of oscillating electric field: III. Interference caused by a double pulse Reviewed

    K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 )   2887 - 2893   2004.10

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    In order to Study consequences of the differences between the ionic-to-neutral and neutral-to-ionic transitions in the one-dimensional extended Peierls-Hubbard model with alternating potentials for the TTF-CA complex, we introduce a double pulse of oscillating electric field in the time-dependent Schrodinger equation and vary the interval between the two pulses as well as their strengths. When the dimerized ionic phase is photoexcited, the interference effect is clearly observed owing to the coherence of charge density and lattice displacements. Namely, the two pulses constructively interfere with each other if the interval is a multiple of the period of the optical lattice vibration, while they destructively interfere if the interval is a half-odd integer times the period, in the processes toward the neutral phase. The interference is strong especially when the pulse is strong and short because the coherence is also strong. Meanwhile, when the neutral phase is photoexcited, the interference effect is almost invisible or weakly observed when the pulse is weak. The photoinduced lattice oscillations are incoherent due to random phases. The strength of the interference caused by a double pulse is a key quantity to distinguish the two transitions and to evaluate the coherence of charge density and lattice displacements.

    DOI: 10.1143/JPSJ.73.2887

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  • On thermo- and photo-induced symmetry-broken transformation in spin-crossover complex: Cooperative activation Reviewed

    T Luty, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 5 )   1237 - 1243   2004.5

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    We study energetics of a cooperative low-spin (L) to high-spin (H) transformation in a crystal with two sublattices, where thermo- and photo-induced symmetry-broken phases have been recently observed. The model takes into account an intra-dimer antiferromatic coupling and inter-dimer couplings. Cooperative activation processes for switching between LH and HL states and that from LL to HH states of a dimer are analyzed. It is shown that locally (within a dimer) preferred symmetry-broken, LH and HL, states compete with inter-dimer couplings, which stimulates dynamical disorder via a decrease in the energy barrier for a flip between asymmetric configurations. On the other hand, a locally non-preferred symmetric state (HH) is supported by inter-dimer interaction via a cooperative activation mechanism. We conclude that symmetry-broken states can form an intermediate thermo-induced phase or can be observed as a photo-induced one at low temperatures as a result of local equilibrium. The global equilibrium follows from cooperative interaction and governs the thermo-induced re-entrant phase transition.

    DOI: 10.1143/JPSJ.73.1237

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  • Two-step photo-induced phase transitions in a two-sublattice model Reviewed

    Y Otsuka, K Yonemitsu

    JOURNAL DE PHYSIQUE IV   114   637 - 639   2004.4

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    As an effective model for the two-step spin transition, we study a two-sublattice spin model that takes into account intra-site anti ferromagnetic and inter-site ferromagnetic Couplings. Due to the competition between these couplings, the temperature dependence of the high spin fraction shows a two-step transition. We perform Monte Carlo (MC) simulations including a photoexcitation term. The MC dynamics of the high spin fraction shows non-linear characteristics such as step-like changes, threshold-like behavior, and phase separation.

    DOI: 10.1051/jp4:2004114152

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  • Ferroelectric phase transition, ionicity condensation, and multicriticality in charge-transfer organic complexes Reviewed

    J Kishine, T Luty, K Yonemitsu

    PHYSICAL REVIEW B   69 ( 7 )   075115 (5 pages)   2004.2

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    To elucidate a pressure-temperature phase diagram of the quasi-one-dimensional mixed-stack charge-transfer complex tetrathiafulvalene-P-chloranil (TTF-CA), we study the quasi-one-dimensional spin-1 Blume-Emery-Griffiths model. In addition to the local charge-transfer energy (Delta) and the inter-stack polar (dipole-dipole) interaction (J(perpendicular to)), we take account of the interstack electrostriction (Coulomb-lattice coupling). Using the self-consistent chain-mean-field theory, where the intra-stack degrees of freedom are exactly treated by the transfer-matrix method, we reproduce the gas-liquid-solid like phase diagram corresponding to the neutral (N), paraelectric ionic (I-para), and ferroelectric ionic (I-ferro) phases, respectively. Our classical model describes an essential point of the multicritical behavior of TTF-CA, i.e., the interchain electrostriction exclusively enhances the charge concentration (ionicity condensation), but does not affect the interchain ferroelectric coupling. This effect leads to appearance of the intermediate I-para phase in between the N and I-ferro phases on the Delta-T phase diagram.

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  • Electronic and lattice dynamics in the photoinduced ionic-to-neutral phase transition in a one-dimensional extended Peierls-Hubbard model Reviewed

    N Miyashita, M Kuwabara, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 9 )   2282 - 2290   2003.9

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    Real-time dynamics of charge density and lattice displacements is studied during photoinduced ionic-to-neutral phase transitions by using a one-dimensional extended Peierls-Hubbard model with alternating potentials for the one-dimensional mixed-stack charge-transfer complex, TTF-CA. The time-dependent Schrodinger equation and the classical equation of motion are solved for the electronic and lattice parts, respectively. We show how neutral domains grow in the ionic background. As the photoexcitation becomes intense, more neutral domains are created. Above threshold intensity, the neutral phase is finally achieved. After the photoexcitation, ionic domains with wrong polarization also appear. They quickly reduce the averaged staggered lattice displacement, compared with the averaged ionicity. As the degree of initial lattice disorder increases, more solitons appear between these ionic domains with different polarizations, which obstruct the growth of neutral domains and slow down the transition.

    DOI: 10.1143/JPSJ.72.2282

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  • Coherence recovery and photoinduced phase transitions in one-dimensional halogen-bridged binuclear platinum complexes Reviewed

    K Yonemitsu, N Miyashita

    PHYSICAL REVIEW B   68 ( 7 )   075113 (9 pages)   2003.8

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    A photoinduced transition from a charge-density-wave (CDW) phase to a charge-polarization (CP) phase has been recently found in a one-dimensional halogen-bridged binuclear platinum complex R-4[Pt-2(pop)(4)I]nH(2)O [pop=P2O5H22-, R=(C2H5)(2)NH2]. Its mechanism is theoretically studied by solving the time-dependent Hartree-Fock equation for a one-dimensional two-band three-quarter-filled Peierls-Hubbard model. Above a threshold in the photoexcitation intensity, a transition takes place from the CDW to CP phases. The threshold intensity depends on the relative stability of these phases, which can be explained qualitatively by their diabatic potentials. However, the transition from the CP to CDW phases is hardly realized for two reasons: (i) low-energy charge-transfer processes occur only within a binuclear unit in the CP phase; (ii) it is difficult for the CDW order to become long ranged owing to its weak coherence. The effective transfer integrals required for the coherence are evaluated.

    DOI: 10.1103/PhysRevB.68.075113

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  • Dynamic spin correlations near neutral-ionic phase transitions Reviewed

    K Yonemitsu

    PHYSICA B-CONDENSED MATTER   329   1219 - 1220   2003.5

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    Near the neutral-ionic phase transition in the one-dimensional extended Hubbard model with alternating potentials at half filling, the effects of alternating transfer integrals and a staggered magnetic field on the local spin excitation spectrum are studied by using the finite-temperature density-matrix renormalization-group method. In the neutral phase, the alternation increases the ionicity and lowers the spin excitation energies toward the ionic phase, while the staggered magnetic field does not modify the spectrum up to a critical field above which the system becomes ionic. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0921-4526(02)02142-7

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  • Photoinduced dynamics of ionicity near the neutral-ionic phase boundary in a one-dimensional extended Peierls-Hubbard model Reviewed

    N Miyashita, M Kuwabara, K Yonemitsu

    SYNTHETIC METALS   135 ( 1-3 )   645 - 646   2003.4

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    Dynamics of the ionicity after photoexcitations in mixed-stack charge-transfer complexes is numerically studied by using a one-dimensional extended Peierls-Hubbard model with alternating potentials at half filling. The time-dependent Schrodinger equation and the Newton equation are solved for the electronic and lattice parts, respectively. Fourier analysis is performed for the ionicity. During the photoinduced phase transition, slow components are dominant and very broad reflecting complex motion of domain walls and lattice displacements. After the transition, fast and slow oscillations are clearly seen, which correspond to the electronic and lattice motion, respectively.

    DOI: 10.1016/S0379-6779(02)00759-2

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  • Photoexcited states and photoinduced dynamics in electronic phases of MMX-chain systems Reviewed

    K Yonemitsu, N Miyashita, M Kuwabara

    SYNTHETIC METALS   135 ( 1-3 )   521 - 522   2003.4

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    In the one-dimensional two-band three-quarter-filled Peierls-Hubbard model for halogen-bridged binuclear metal complexes R-4[Pt-2(pop)(4)I]nH(2)O with counter ion R and pop=P2O5H22-, a transition from the charge-density-wave phase to the charge-polarization phase is photoinduced, but the opposite process is not. Its origin is explained by considering differences in low-energy photoexcitations in the two phases and coherence of respective order parameters. The different dynamics is demonstrated by solving the time-dependent Schrodinger equation.

    DOI: 10.1016/S0379-6779(02)00712-9

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  • Self-doping effect on the Mott transition accompanied with threefold charge ordering in (DCNQI)(2)Cu Reviewed

    M Kuwabara, K Yonemitsu, H Ohta

    SYNTHETIC METALS   133   295 - 297   2003.3

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    The commensurate state with threefold lattice distortion in the insulating phase of (DCNQI)(2)Cu is studied based on a two-band Peierls-Hubbard model by using the density-matrix renormalization-group method. With strong electron correlation among the d electrons, self-consistent lattice modulation strongly blocks the charge transfer between the pi and d orbitals in order to keep the commensurability condition even when the pi-d level difference is widely varied. A transition to an incommensurate phase requires a large deviation of the pi-d level difference from the optimal case. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0379-6779(02)00315-6

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  • Correlation-induced dimensional crossovers of charge-transfer excitations in quasi-one-dimensional organic conductors Reviewed

    K Yonemitsu

    SYNTHETIC METALS   133   7 - 9   2003.3

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    Applying the finite-temperature density-matrix renormalization-group method to the spinless fermion model on a two-leg ladder, we have calculated the dynamical structure factors for the local charge transfer processes along and across the chains. The intra-chain excitation spectra are sensitive to the inter-chain transfer integral and the chemical potential, while the inter-chain excitation spectra are sensitive to the intra-chain electron correlation. These dynamical properties are due to the collective motions of fermions along the chains and the energy-dependent confinement of fermions in the chains. At low but finite energies, the effects of the increasing inter-chain transfer integral on the local charge-transfer spectra are similar to those of the chemical potential deviating from zero. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0379-6779(02)00422-8

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  • Domain-wall dynamics after photoexcitations near neutral-ionic phase transitions Reviewed

    N Miyashita, M Kuwabara, K Yonemitsu

    PHASE TRANSITIONS   75 ( 7-8 )   887 - 893   2002.10

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    Real-time dynamics of domain walls between the neutral and ionic phases just after photoexcitations is studied by fully solving the time-dependent Schrodinger equation for a one-dimensional extended Peierls-Hubbard (PH) model, not by relying on the adiabatic approximation. The unrestricted Hartree-Fock (HF) approximation is used for electrons, and the lattice displacements are treated classically. Three characteristic time scales are observed: rapid oscillation of ionicity owing to the local charge transfer; slow oscillation of lattice displacements; and even slower and collective motion of domain walls. Steady growth of a metastable domain is achieved after complicated competition of micro domains. The relevance to recently measured, time-resolved photoreflectance spectra in TTF-CA is discussed.

    DOI: 10.1080/01411590290034029

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  • Variation of excitation spectra in mixed-stack charge-transfer complexes Reviewed

    K Yonemitsu

    PHASE TRANSITIONS   75 ( 7-8 )   759 - 767   2002.10

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    Local excitation spectra in different spin and charge channels are calculated in the one-dimensional extended Hubbard model with alternating energy levels at half filling for mixed-stack charge-transfer complexes. Near the boundary between the neutral and ionic phases, the electronic system is easily distorted by an additional term that reduces the symmetry and opens a gap. Alternating transfer integrals produce a nonmagnetic spin-Peierls phase; while staggered magnetic fields produce an antiferromagnetic phase. Both of them enhance the ionicity when they are introduced into the neutral phase near the boundary. Accordingly, these additional terms enhance low-energy spin excitations, although these excitations are suppressed when compared with those in the regular ionic phase. The regular ionic phase has a larger spectral weight in the local current channel than the neutral phase. This would imply that, in one dimension and if the lattice effect is negligible, the ionic phase has smaller activation energy in the electric conductivity near the boundary than the neutral phase.

    DOI: 10.1080/01411590290033877

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  • Collective excitations and confinement in the excitation spectra of the spinless fermion model on a ladder Reviewed

    K Yonemitsu

    PHYSICAL REVIEW B   66 ( 3 )   035121 (10 pages)   2002.7

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    Intrachain and interchain local charge-transfer excitation spectra and the single-particle density of states are calculated in the spinless fermion model on a ladder with varying intrachain nearest-neighbor repulsion and interchain transfer integral at and near half filling by using the finite-temperature density-matrix renormalization-group method. Collective excitations are found to govern the low-energy intrachain spectra, while only individual local excitations are present in the interchain spectra. For strong intrachain repulsion, the low-energy motion of fermions is confined within a chain. The interchain motion of fermions is not bandlike but incoherent. As a consequence, the low-energy intrachain spectra are sensitive at half filling to the interchain transfer integral that weakens the density-density correlation along the chains. Similarly, the low-energy intrachain spectra are sensitive near half filling to the chemical potential that reduces the effect of the umklapp process. Similarities are pointed out between these findings and the experimentally observed, optical conductivity spectra in the quasi-one-dimensional organic conductors (TMTSF)(2)X.

    DOI: 10.1103/PhysRevB.66.035121

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  • Finite-temperature phase diagram of mixed-stack charge-transfer complexes Reviewed

    K Yonemitsu

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   63 ( 6-8 )   1495 - 1499   2002.6

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    The mixed-stack organic charge-transfer complex, (BEDO-TTF)(Cl(2)TCNQ), has shown a phase transition accompanied with a sharp drop in the magnetic susceptibility and with an increase in the intermolecular overlap, as the temperature is lowered. Here, we theoretically consider the possibility for a phase transition from the ionic phase to a neutral phase, which is driven by charge-transfer fluctuations. Using finite-temperature density-matrix renormalization-group calculations for the one-dimensional extended Hubbard model with alternating potentials, we show that, with increasing transfer integral t, a transition from the neutral phase to the ionic phase is induced by spin fluctuations for small t, while another transition from the ionic phase to the neutral phase is induced by charge-transfer fluctuations for large t. Near the phase boundary, the free energy is easily lowered by dimerization of transfer integrals or by staggered magnetic field. Thus, a further transition is also possible to a dimerized nonmagnetic phase or to an antiferromagnetic phase at a lower temperature. In two dimensions, we expect that the effect of charge-transfer fluctuations is larger and that the transition to the dimerized nonmagnetic phase is suppressed. (C) 2002 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0022-3697(02)00043-4

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  • Lattice and magnetic instabilities near the neutral-ionic phase transition of the one-dimensional extended Hubbard model with alternating potentials in the thermodynamic limit Reviewed

    K Yonemitsu

    PHYSICAL REVIEW B   65 ( 20 )   205105 (8 pages)   2002.5

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    The effects of dimerization causing the alternation of transfer integrals on the neutral-ionic phase transition are studied in the one-dimensional extended Hubbard model with alternating potentials at half filling. The finite-temperature density-matrix renormalization-group method is used to treat the thermodynamic limit. In the ionic phase, the free-energy gain is proportional to delta(4/3) with delta being the degree of dimerization even near the phase boundary at low temperatures. In the neutral phase, the free-energy gain is quadratic for small transfer integral far from the phase boundary, but it is nonlinearly enhanced near the boundary. Large transfer integrals make the gain faster than delta(2), so that they facilitate dimerization. The dimerization in the neutral phase increases the ionicity and lowers the spin excitation energies. These lattice effects are in contrast to the effects of a staggered magnetic field. The relevance of these results to recently observed dimerization in the neutral phase of ClMePD-DMeDCNQI is discussed.

    DOI: 10.1103/PhysRevB.65.205105

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  • Dimensional crossovers and phase transitions in strongly correlated low-dimensional electron systems: Renormalization-group study Reviewed

    JI Kishine, K Yonemitsu

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   16 ( 5 )   711 - 771   2002.2

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    Based on the perturbative renormalization-group (PRO) approach, we have examined interplay or competition between one-particle (1P) and two-particle (2P) processes in strongly correlated low-dimensional electron systems. Throughout the article, we use the Grassmann functional integral approach, since it has an advantage that the 1P degrees of freedom are incorporated in an explicit manner. We mainly discuss an array of chains weakly-coupled via interchain one-particle hopping, where the constituent chains, if isolated, have a strong-coupling fixed point, such as the Mott-insulator, spin-gap-metal, or Anderson-insulator fixed point. In such cases, quantum fluctuations evolving toward the low-energy limit strongly suppress the interchain 1P coherence, and consequently a phase transition from the incoherent metallic (ICM) phase becomes possible. This kind of competition plays a key role to elucidate the interplay of correlation and dimensionality effects in real quasi-one-dimensional (Q1D) materials in nature. As examples, we take up spin-density-wave (SDW) phase transitions in dimerized quarter-filled Hubbard chains to elucidate the nature of the magnetic phase transitions in the Q1D organic conductors, (TMTTF)(2)X and (TMTSF)(2)X. Dimensional crossover problems in Q1D Hubbard ladders are also discussed to describe the pressure-induced superconductivity in the doped ladder systems. Interplay of randomness, electron correlation, and dimensionality effects in weakly-coupled half-filled Hubbard chains with weak quenched random potentials is also studied. We also discuss some 2D electron systems where the two-loop renormalization-group procedure is well defined and works.

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  • Quantum and thermal charge-transfer fluctuations for neutral-ionic phase transitions in the one-dimensional extended Hubbard model with alternating potentials Reviewed

    K Yonemitsu

    PHYSICAL REVIEW B   65 ( 8 )   085105 (7 pages)   2002.2

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    Effects of quantum and thermal fluctuations on transitions between the ionic phase and the neutral phase are studied by applying the finite-temperature density-matrix renormalization-group method to, the one-dimensional extended Hubbard model with alternating potentials at half filling. Charge-transfer fluctuations lower the energy of the neutral phase more than that of the ionic phase, which is in contrast to the spin fluctuations favoring, the ionic phase. As a consequence, with increasing intermolecular overlap between the neighboring donor and acceptor sites, we expect a spin-fluctuation-induced transition from the neutral phase to the ionic phase, and a charge-transfer-fluctuation-induced transition from the ionic phase to the neutral phase, near the phase boundary. Relevance to a recently observed phase transition in a, new class of mixed-stack, charge-transfer complexes is discussed.

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  • Charge ordering patterns and their excitation spectra in two-dimensional charge-transfer compounds Reviewed

    M Mori, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   380   209 - 213   2002

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    We calculate optical conductivity spectra for various charge ordering (CO) states in the two-dimensional extended Hubbard model at quarter filling with the random phase approximation. The results are examined from a viewpoint of the atomic limit. We compare our results with the measured spectra for the theta-(ET)(2)X salts and discuss the CO patterns and their charge excitations realized in these compounds.

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  • Optical conductivity for possible ground states of dimerized two-band Pd(dmit)(2) salts Reviewed

    M Mori, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   376   141 - 146   2002

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    We have studied the optical conductivity for possible ground states of Pd(dmit)(2) salts, exactly diagonalizing a two-band Hubbard model for a dimer. Our results reproduce dominant peaks of the optical spectra measured by Tajima et al. and confirm their argument from the strong-coupling viewpoint. Interaction strengths are estimated and used to study the stability of magnetic orders.

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  • Optical excitations in XMMX monomers and MMX chains Reviewed

    M Kuwabara, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   376   251 - 256   2002

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    We theoretically study optical excitations in K-4[Pt-2(pop)(4)X-2] monomers (X=Cl, Br, I), using an extended Hubbard model. We show that long-range transfer integrals and long-range Coulomb interactions are substantially large to reproduce the experimental results, and discuss effects of long-range Coulomb interactions on the electronic phases and the optical conductivity spectra of the MMX chains.

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  • Spin solitons in the alternate charge polarization background of MMX chains Reviewed

    M Kuwabara, K Yonemitsu, H Ohta

    EPR IN THE 21ST CENTURY: BASICS AND APPLICATIONS TO MATERIAL, LIFE AND EARTH SCIENCES   59 - 62   2002

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    We study spin solitons in the alternate charge polarization background of the MMX chains, using the unrestricted Hartree-Fock approximation to a one-dimensional Peierls-Hubbard model. The effects of the electron-lattice coupling and the electron-electron interaction on the shape of the soliton are discussed.

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  • Intra- and inter-chain excitations near a quantum phase transition in quasi-one-dimensional conductors Reviewed

    K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   376   53 - 58   2002

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    We study intra- and inter-chain excitation spectra near a quantum phase transition in a spinless fermion model on a two-leg ladder at half filling by the finite-temperature density-matrix renormalization-group method. Above a critical strength of intrachain nearest-neighbor repulsion, a gap appears, accompanied with a long-range order of density modulation in the checkerboard pattern at zero temperature. The intrachain excitation spectra do not change so much in the gapless phase below the critical strength, while the interchain excitation spectra are considerably altered by the intrachain repulsion even in the gapless phase. Relevance to the optical conductivity in quasi-one-dimensional electron systems is suggested.

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  • Strong commensurability effect on metal-insulator transition in (DCNQI)(2)Cu Reviewed

    M Kuwabara, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   380   257 - 261   2002

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    Stability of three-fold lattice distortion in the insulating state of (DCNQI)(2)Cu is studied by exactly diagonalizing a two-band Peierls Hubbard model on the 6 x 2 lattice. Self-doping is essentially important and caused by strong commensurability pinning, which are a consequence of moderate coupling of DCNQI pi electrons with lattice and strong correlation of Cu d electrons.

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  • Variation mechanisms of ground-state and optical-excitation properties in quasi-one-dimensional two-band electron systems Reviewed

    K Yonemitsu, M Kuwabara, N Miyashita

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   379   467 - 474   2002

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    We study i) the ground-state and optical-excitation properties of halogen-bridged binuclear metal complexes, which are known as MMX chain compounds, by the strong-coupling expansion for a one-dimensional two-orbital extended Peierls-Hubbard model, and ii) the dynamics of domain walls between the neutral and ionic phases in mixed-stack charge-transfer complexes, by solving the time-dependent Schrodinger equation for a one-dimensional extended Peierls-Hubbard model with alternating energy levels. We find in i) that competition between electron-electron and electron-lattice interactions and competition between short- and long-range interactions are both important for the electronic phase variation, and in ii) that charge and lattice dynamics immediately after photoexcitations is complex and not explained simply within the domino picture.

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  • Photoinduced phenomenon in polymers Reviewed

    Sun, X, RL Fu, K Yonemitsu, K Nasu

    PHYSICAL REVIEW A   64 ( 3 )   032504 (7 pages)   2001.9

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    Numerical simulation has shown that a polymeric molecule can possess a photoinduced phenomenon-photoinduced polarization reversion-in which the electric dipole of the polymeric molecule is reversed by absorbing one photon. This paper provides an analytic theory by means of a response function to prove that a polymeric molecule with a bipolaron has a negative static polarizability and explains the physical origin of this photoinduced phenomenon in detail. This paper also presents a dynamical calculation for the photoinduced polarization reversion, from which the relaxation time for the dipole reversion can be determined.

    DOI: 10.1103/PhysRevA.64.032504

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  • Two-loop renormalization of the quasiparticle weight in two-dimensional electron systems Reviewed

    Jun-Ichiro Kishine, Nobuo Furukawa, Kenji Yonemitsu

    International Journal of Modern Physics B   15 ( 10-11 )   1381 - 1384   2001.5

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    We apply the renormalization-group (RG) approach to two model systems where the two-dimensional Fermi surface has portions which give rise to the logarithmically singular two-loop self-energy process.

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  • Charge excitations in an alternate charge polarization phase of a one-dimensional two-band extended Peierls-Hubbard model for MMX chains Reviewed

    M Kuwabara, K Yonemitsu

    SYNTHETIC METALS   120 ( 1-3 )   947 - 948   2001.3

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    We investigate the optical conductivity of a halogen-bridged binuclear metal complex in an alternate-charge-polarization phase, using a one-dimensional two-band extended Peierls-Hubbard model and the Lanczos technique, to study the dependence of three main peaks ascribed to intradimer, interdimer and halogen-to-metal charge excitations on model parameters.

    DOI: 10.1016/S0379-6779(00)01196-6

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  • Intra- and inter-chain dynamic response functions in quasi-one-dimensional conductors Reviewed

    K Yonemitsu

    SYNTHETIC METALS   120 ( 1-3 )   845 - 846   2001.3

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    Intra- and inter-chain excitation spectra are studied in a spinless fermion model on a two-leg ladder at half filling. Numerical results are obtained by application of the density matrix renormalization group technique to the quantum transfer matrix for infinite systems. Near the metal-insulator transition, the intra-chain Coulomb repulsion is found to affect local current correlation more sensitively in the rung direction than in the leg direction.

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  • Stability and cation dependence of magnetic orders in (Et(n)Me(4-n)Z)[Pd(dmit)(2)](2) Reviewed

    M Mori, K Yonemitsu

    SYNTHETIC METALS   120 ( 1-3 )   945 - 946   2001.3

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    The cation dependence of the magnetic phase transitions in the Pd(dmit)(2) salts is studied by calculating effective exchange interactions between spins on dimers in a two-band Hubbard model. For Et2Me2Sb, the antiferromagnetic order is shown to be destroyed by magnetic frustration within the linear spin wave theory.

    DOI: 10.1016/S0379-6779(00)01476-4

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  • Charge ordering and lattice modulation in MMX chains Reviewed

    M Kuwabara, K Yonemitsu

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   62 ( 1-2 )   435 - 438   2001.1

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    Ground state phase diagrams for the MMX chains are studied in a one-dimensional two-band model by exactly diagonalizing 18-site clusters. Experimentally observed phases are reproduced by changing relative strengths of an electron-lattice coupling the interdimer transfer integral, and an elastic constant, whose variation is roughly estimated from the interatomic spacing, the species of the halogen ion, and the presence/absence of counter ions. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0022-3697(00)00183-9

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  • Charge gap and dimensional crossovers in quasi-one-dimensional organic conductors Reviewed

    K Yonemitsu, J Kishine

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   62 ( 1-2 )   99 - 104   2001.1

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    Quasi-one-dimensional quarter-filled organic conductors, (TMTTF)(2)X and (TMTSF)(2)X, show a dimensional crossover, and their electronic properties change accordingly. We describe this using the two-loop perturbative and density-matrix renormalization-group methods, the epsilon expansion around one dimension, and the random phase approximation, The effect uf dimerization on the charge gap and interchain one-particle coherence is clarified. The effect of random potentials is also studied to describe the Mott insulator, Anderson localization, and metallic phases of (DCNQI)(2)Ag(1-x)Cu(x) mixed crystals. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0022-3697(00)00108-6

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  • Anisotropic collective excitations around various charge ordering states Reviewed

    M Mori, K Yonemitsu

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   62 ( 1-2 )   409 - 411   2001.1

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    We calculate absorption spectra for various charge ordering (CO) states in the two-dimensional extended Hubbard model at quarter filling with the random phase approximation. Each CO state has: its own characteristic and anisotropic excitations. In principle, these features should be observed in the optical measurements and tell which CO state is realized in the theta-(ET)(2)X salts. (C) 2000 Elsevier Science Ltd. All rights reserved.

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  • Ground state phases and optical properties in extended Peierls-Hubbard models for halogen-bridged binuclear metal complexes Reviewed

    M Kuwabara, K Yonemitsu

    JOURNAL OF MATERIALS CHEMISTRY   11 ( 9 )   2163 - 2175   2001

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    Mechanisms Of a variety of charge and lattice ordered phases observed in halogen-bridged binuclear metal complexes are theoretically studied by applying the exact diagonalization and strong-coupling expansion methods to one- and two-band extended Peierls-Hubbard models. In R-4[Pt-2(pop)(4)I]nH(2)O [R=Na, K, NH4, (CH3(CH2)(7))(2)NH2, etc., pop=P2O5H22-] containing charged MMX chains, three electronic phases are suggested by experiments, We find that the variation of the electronic phases originates not only from competition between site-diagonal electron-lattice and electron-electron interactions but also from competition between short-range and long-range electron-electron interactions. On the other hand, in Pt-2(RCS2)(4)I (R = CH3, n-C4H9) containing neutral MMX chains, a site-off-diagonal electron-lattice interaction and the absence of counter ions are found to be crucial to produce the recently found, ordered phase. The optical conductivity spectra are also studied, which directly reflect the electronic phases. Their dependence on the electronic phase and on model parameters is clarified from the strong-coupling viewpoint.

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  • Charge ordering and optical conductivity of MMX chains Reviewed

    M Kuwabara, K Yonemitsu

    PHYSICS IN LOCAL LATTICE DISTORTIONS: FUNDAMENTALS AND NOVEL CONCEPTS LLD2K   554   465 - 469   2001

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    We study the optical conductivity of the halogen-bridged binuclear metal complexes, using a one-dimensional dimerized 3/4-filled-band model and the Lanczos method. The spectra are quite sensitive to the charge ordering pattern and the long-range Coulomb interaction.

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  • Interplay of randomness, electron correlation, and dimensionality effects in quasi-one-dimensional conductors Reviewed

    J. Kishine, K. Yonemitsu

    Physical Review B - Condensed Matter and Materials Physics   62 ( 20 )   13323 - 13337   2000.11

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    We study the interplay of randomness, electron correlation, and dimensionality effects in weakly coupled half-filled Hubbard chains with weak quenched random potentials, based on the renormalization-group (RG) approach. We perform a two-loop RG analysis of an effective action derived by using the replica trick, and examine the following crossovers and phase transitions from an incoherent metal regime: (1) a crossover to the Anderson localization regime, (2) an antiferromagnetic phase transition, and (3) a crossover to the quasi-one-dimensional weak-localization regime. The case of d = 1 + ε (ε≪ 1) dimensions is also mentioned.

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  • Dimensionality effects on the charge gap in the dimerized Hubbard model at quarter filling: The density-matrix and perturbative renormalization-group approaches Reviewed

    K Yonemitsu, J Kishine

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   69 ( 7 )   2107 - 2112   2000.7

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    We study dimensionality effects on the charge gap in the dimerized Hubbard model at quarter filling, with two approaches. First, we examine three chains coupled via the interchain one-particle hopping integral t(b), by the density-matrix renormalization-group (DMRG) method. Next, we consider the d = 1 + epsilon dimensional model, using the perturbative renormalization-group (PRG) method. The dimensionality is controlled through t(b) and epsilon, respectively. Both approaches lead to the conclusion that, for a finite dimerization ratio, the charge gap decreases as the dimensionality increases.

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  • Magnetic property of MMX chains as dimerized quarter-filled systems Reviewed

    M Kuwabara, K Yonemitsu

    PHYSICA B   284   1545 - 1546   2000.7

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    We study ground state phase diagrams for the MMX chains, using a one-dimensional dimerized 3/4-filled extended Hubbard-Peierls model with site diagonal and off-diagonal electron-lattice interactions. The ground states are obtained both in the Hartree-Fock approximation and by the exact diagonalization. We discuss magnetic properties of the MMX chains, (C) 2000 Elsevier Science B.V. All rights reserved.

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  • Dimensionality effects in half-filled random Hubbard chains Reviewed

    J Kishine, K Yonemitsu

    PHYSICA B   284   1946 - 1947   2000.7

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    We discuss interplay of randomness, electron correlation and dimensionality effects in half-filled random Hubbard chains. Low-temperature phases are given based on the two-loop renormalization group (RG) analysis. Feedback effects of interchain processes on the umklapp process are examined by the 1 + epsilon expansion. We comment on the relevance of the present result to a phase diagram of a doped organic compound, (DI-DCNQI)(2)Ag1 - xCux. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

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  • Effects of dimerization on spin, charge and hopping correlation functions in quasi-one-dimensional organic conductors Reviewed

    K Yonemitsu

    PHYSICA B   284 ( Pt.1 )   515 - 516   2000.7

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    In order to see the effects of dimerization, interchain hopping, and nearest-neighbor repulsion on various one- and two-body correlation functions in quasi-one-dimensional organic conductors, (TMTTF)(2)X and (TMTSF)(2)X, we apply the density matrix renormalization group method to a three-chain extended Hubbard model at quarter filling. The hopping correlation function shows that the interchain one-particle coherence is strongly suppressed when a charge gap due to the dimerization is larger than the interchain hopping integral. Meanwhile, the spin-spin and charge-charge correlation functions show that the interchain particle-hole coherence is rather insensitive. The charge-charge correlation function is more sensitive to the nearest-neighbor repulsion than the charge gap. (C) 2000 Elsevier Science B.V. All rights reserved.

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  • Possible ground-state phases of Pd(dmit)(2) salts Reviewed

    M Mori, K Yonemitsu, H Kino

    PHYSICA B   284   1495 - 1496   2000.7

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    We have studied possible ground-state phases of Pd(dmit)(2) salts using the two-band Hubbard model. From a strong coupling expansion, an effective model is derived and used to describe low-energy excitations. It is found that mutual interactions and dimensionality of effective bands cooperatively determine the transport and magnetic properties. (C) 2000 Elsevier Science B.V. All rights reserved.

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  • Photoinduced polarization inversion in a polymeric molecule Reviewed

    Sun, X, RL Fu, K Yonemitsu, K Nasu

    PHYSICAL REVIEW LETTERS   84 ( 13 )   2830 - 2832   2000.3

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    The polymeric molecule can exhibit a new photoinduced phenomenon where the electric dipole of the molecule with a bipolaron is reversed by absorbing one photon. This photoinduced polarization inversion occurred in a single molecule is an ultrafast process with a relaxation time of 200 fs.

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  • Role of dimensionality in dimerized two-band systems Reviewed

    M Mori, K Yonemitsu, H Kino

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   341   1353 - 1358   2000

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    We have studied the ground state properties of Pd(dmit)(2) salts using an effective dimer model. This model describes low-energy excitations of the two-band Hubbard model and is derived by a strong coupling expansion. Dimensionality of the Fermi surface, density-of-states singularity, and magnetic frustration in the dimer model are simultaneously controlled by substituting the cation.

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  • Charge ordering and lattice modulation in quasi-one-dimensional halogen-bridged binuclear metal complexes Reviewed

    M Kuwabara, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   343   365 - 370   2000

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    Ground state phase diagrams of the MMX chains ale studied in a one-dimensional dimerized 3/4-filled model by exactly diagonalizing 12-site clusters. Experimentally observed phases are reproduced by changing relative strengths of an electron-lattice coupling, the inter-dimer transfer integral, and an elastic constant whose variation is roughly estimated from the interatomic spacing, the species of the halogen ions and the presence/absence of counter ions.

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  • Collective excitations around charge ordered states and coexistent states with different orders Reviewed

    M Mori, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   343   539 - 544   2000

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    We study qualitative differences of excited states between a charge ordered state and a charge uniform state. The excited states are calculated in the random phase approximation for the one-dimensional extended Hubbard model at quarter Filling. In the charge ordered state, a dominant excitation in the current-current correlation function has no charge density modulation. A dominant excitation in the charge uniform state originates from crossing the dimerization gap and modulates the charge density.

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  • Interplay of correlation, randomness and dimensionality effects in weakly-coupled half-filled random Hubbard chains Reviewed

    Jun-Ichiro Kishine, Kenji Yonemitsu

    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals   341   555 - 560   2000

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    We study interplay of electronic correlation, randomness and dimensionality effects in half-filled random Hubbard chains weakly coupled via an interchain one-particle hopping. Based on the two-loop renormalization-group approach, phase diagrams are given in terms of temperature vs. strengths of the intrachain electron-electron umklapp scattering, the random scattering and the interchain one-particle hopping.

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  • Numerical studies of ground state phase diagrams for the MMX chains Reviewed

    M Kuwabara, K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   341   1337 - 1342   2000

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    We study ground state phase diagrams for the MMX chains, using a one-dimensional dimerized 3/4-filled extended Hubbard-Peierls model with sire diagonal and off-diagonal electron-lattice interactions. The ground states no obtained mainly in the Hartree-Fock approximation, and their accuracy is checked by the exact diagonalization of small clusters. We find a new phase in addition to Frequently considered phases and compare our results with experimental results.

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  • Charge gap and interchain correlation in quasi-one-dimensional dimerized organic conductors Reviewed

    K Yonemitsu

    MOLECULAR CRYSTALS AND LIQUID CRYSTALS   341   1347 - 1352   2000

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    We study the relation between the charge gap and the interchain one-body correlation function in quasi-one-dimensional dimerized organic conductors at quarter filling, by applying the density matrix renormalization group method to a three-chain extended Hubbard model. The charge gap increases with the degree of dimerization in the intrachain hopping integrals. When the charge gap is larger than the interchain hopping integral, the interchain hopping correlation is strongly suppressed, as observed in the (TMTTF)(2)X salts.

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  • Phase transitions from incoherent and from coherent metal phases in quasi-one-dimensional organic conductors Reviewed

    J Kishine, K Yonemitsu

    JOURNAL OF LOW TEMPERATURE PHYSICS   117 ( 5-6 )   1741 - 1745   1999.12

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    We study effects of a preformed Mott yap and dimensionality on interchain one-particle coherence and spin-density-wave phase transitions in weakly-coupled dimerized quarter-filled Hubbard chains. A phase diagram is given, based on the two-loop perturbative renormalization-group (RG) approach together with the random phase approximation. Feedback effects of interchain processes on the umklapp process are examined by the 1 + epsilon expansion. We discuss relevance of the present result to the SDW phase transitions in the quasi-one-dimensional dimerized quarter-filled organic conductors, (TMTTF)(2)X and (TMTSF)(2)X.

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  • Magnetic and pairing correlation functions and interchain coherence in quasi-one-Dimensional dimerized organic conductors Reviewed

    K Yonemitsu

    JOURNAL OF LOW TEMPERATURE PHYSICS   117 ( 5-6 )   1765 - 1769   1999.12

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    We study how magnetic and pairing correlation evolves with an increasing interchain hopping integral and decreasing dimerization of intrachain hopping integrals, by applying the density matrix renormalization group (DMRG) method to a three-chain extended Hubbard model at quarter filling for quasi-one-dimensional organic conductors, (TMTTF)(2)X and (TMTSF)(2)X. Magnetic correlation changes from weakly coupled chains of large-amplitude spin density waves to an interchain-coherence-developed spin density wave. Pairing correlation increases, though it Still decays exponentially owing to a charge gap for parameters considered here.

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  • Quasi-one-dimensional natures in (Et(n)Me(4-n)Z) [Pd(dmit)(2)](2) Reviewed

    M Mori, K Yonemitsu, H Kino

    JOURNAL OF LOW TEMPERATURE PHYSICS   117 ( 5-6 )   1723 - 1727   1999.12

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    We studied one of possible grounded states for Pd(dmit)(2) salts in a dimerized two-band Hubbard model. By using a, strong-coupling expansion, we obtained an effective dimer model which has a quasi-one-dimensional Fermi surface. In the insulating phase, it leeds to the Heisenberg model on an anisotropic triangular lattice. We calculated effective exchange coupling strengths within. the second order perturbation theory and found that both ferromagnetic and antiferromagnetic couplings are possible. Similarities to and differences from Ni(dmit)(2) salts are discussed.

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  • Structures and electronic phases of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) clusters and kappa-(BEDT-TTF) salts: A theoretical study based on ab initio molecular orbital methods Reviewed

    Y Imamura, S Ten-no, K Yonemitsu, Y Tanimura

    JOURNAL OF CHEMICAL PHYSICS   111 ( 13 )   5986 - 5994   1999.10

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    Electronic and geometrical structures of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules are studied using ab initio molecular orbital methods. The optimized structure of a BEDT-TTF monomer is close to the experimental one within errors of 0.02 Angstrom and 0.5 deg in bond length and angle, respectively, except the ethylene group. Ab initio parameters such as transfer integrals and Coulomb interactions are determined from the BEDT-TTF dimer and tetramer calculations. Using model Hamiltonians with the ab initio parameters, we investigate the electronic states based on the exact diagonalization method. The results show that the ground state has antiferromagnetic correlation which is consistent with experimental results. We study the effects of long-range Coulomb interactions employing the 2-D extended Hubbard model with the Hartree-Fock approximation. It is found that the ground state shows various phases; antiferromagnetic, charge ordering, and paramagnetic ones, controlled by the long-range interactions. (C) 1999 American Institute of Physics. [S0021- 9606(99)30437-2].

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  • Spin-density-wave phase transitions in quasi-one-dimensional dimerized quarter-filled organic conductors Reviewed

    J Kishine, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   68 ( 8 )   2790 - 2801   1999.8

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    We have studied spin density wave (SDW) phase transitions in dimerized quarter-filled Hubbard chains weakly coupled via interchain one-particle hopping, t(bO). It is shown that there exists a critical value of t(bO), t(b)*, between the incoherent metal regime (t(bO) < t(b)*) and the Fermi liquid regime (t(bO) > t(b)*) in the metallic phase above the SDW transition temperature. By using the 2-loop perturbative renormalization-group (PRG) approach together with the random-phase-approximation, we propose a SDW phase diagram covering both of the regimes. The SDW phase transition from the incoherent metal phase for t(bO) < t(b)* is caused by growth of the intrachain electron-electron umklapp scattering toward low temperatures, which is regarded as preformation of the Mott gap. We discuss relevance of the present result to the SDW phase transitions in the quasi-one-dimensional dimerized quarter-filled organic conductors, (TMTTF)(2)X and (TMTSF)(2)X.

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  • Electric-field response of exciton in electroluminescent polymer Reviewed

    L Li, RL Fu, Sun, X, K Yonemitsu

    PHYSICA STATUS SOLIDI B-BASIC RESEARCH   214 ( 2 )   337 - 342   1999.8

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    In electroluminescent polymers, the exciton is polarized by a weak electric field E and dissociated by strong E. These effects can quantitatively elucidate the observed dependence of the luminous intensity of the luminescent polymer on the electric field and the field-induced charge generation in conjugated polymers.

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  • Effects of dimerization and interchain one-particle hopping in a weakly coupled dimerized chain system at quarter filling Reviewed

    J Kishine, K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   1833 - 1834   1999.6

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    Effects of the intrachain dimerization and the interchain one-particle hopping, t(b), in a quasi-one-dimensional dimerized chain system at quarter filling have been studied, based on the perturbative renormalization group (PRG) approach. Based on the results, we discuss difference in the low-energy properties between TMTTF and TMTSF compounds.

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  • Renormalization-group study of competition between density waves and pairing in quasi-one-dimensional electron systems Reviewed

    K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   2216 - 2217   1999.6

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    We study crossover from the doped two-leg ladder system to a quasi-one-dimensional system by an inter-ladder one-particle process and stability of the superconducting phase, using a renormalization-group method and differentiating the contributions from the particle-particle channel and those from the particle-hole channel. Effects of electron-2k(F) phonon and electron-4k(F) phonon couplings are also investigated.

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  • Coexistence of SDW and purely-electronic CDW in quarter-filled organic conductors Reviewed

    M Ogata, N Kobayashi, K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   2242 - 2243   1999.6

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    Recently an X-ray experiment reported a coexisting phase of purely-electronic 2k(F) charge density wave (CDW) and the conventional 2k(F) spin density wave (SDW) in (TMTSF)(2)PF6. In order to understand such coexistence, we have performed a mean-field calculation for a Hubbard-type model of a quarter-filled one-dimensional chain. It is found that the coexistence of 2k(F) SDW and purely-electronic 2k(F) CDW is realized due to the effect of next-nearest-neighbor Coulomb repulsion. Phase diagrams are obtained as a function of nearest- and next-nearest-neighbor Coulomb interaction energies. Competition between the two coexistent states with 2k(F) CDW and with 4k(F) CDW is revealed, which gives a first order transition. It turns out that the internal degrees of freedom inside a dimer (consisting of two TMTSF molecules) play an important role. Our result supports the X-ray result of a coexisting phase in (TMTSF)(2)PF6.

    DOI: 10.1016/S0379-6779(98)00567-0

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  • Possible magnetic phases in two-band systems with different dimensionality Reviewed

    M Mori, K Yonemitsu, H Kino

    SYNTHETIC METALS   103 ( 1-3 )   1883 - 1884   1999.6

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    The ground states of the molecular conductors (Me(4)Z)[Pd(dmit)(2)](2), which have strong dimerization and two bands with different dimensionality, have been studied based on the Hartree-Fock approximation. The results indicate that two different magnetic orders appear depending on both the energy difference between the two bands and the strength of the Coulomb interaction. To clarify the origin of the magnetic orders, exchange interactions between dimers have been calculated within the second-order perturbation theory with respect to the inter-dimer transfer integrals. We have found that the different magnetic orders are due to the different symmetry of the molecular orbitals.

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  • Conductivity and magnetic properties of one-dimensional Heisenberg-Kondo lattice Reviewed

    T Ogawa, K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   2149 - 2150   1999.6

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    Using the one-dimensional quarter-filled Heisenberg-Kondo lattice model for a pi-d electron system, CoPc(AsF6)(0.5), we study the effects of long-range Coulomb interaction among pi electrons on the conductivity. The density-matrix renormalization-group method is employed. As a first, step, we regard the localized spins of d electrons as classical ones, and then, as quantum S=1/2 spins, which are coupled antiferromagnetically with each other. In the former case, d electrons produce a static staggered magnetic field for pi electrons. It is pointed out that the next-nearest-neighbor repulsion among a electrons and the magnetic coupling between pi and d electrons are essential to open a charge gap.

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  • Anisotropic renormalization-group flow of quasiparticle weight in a two-dimensional electron system with a partially flat Fermi surface Reviewed

    J Kishine, K Yonemitsu

    PHYSICAL REVIEW B   59 ( 23 )   14823 - 14826   1999.6

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    Two-loop renormalization-group (RG) analysis for a two-dimensional electron system with a partially Bat Fermi surface has been carried out. We found that the RG flow of the quasiparticle weight depends on the location of the electron wave number k on the Fermi surface due to the kinematical restriction to the logarithmically divergent processes in the flat regions of the Fermi surface.

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  • A correlated-basis-function study of SDW in polymers Reviewed

    XH Xu, RT Fu, Sun, X, K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   2337 - 2338   1999.6

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    We study spin-density wave (SDW) in polymers, using screened Coulomb potential to describe full electron interaction in the broad-band systems and developing a spin-dependent correlated-basis-function method to handle the correlation effect. The SDW is shown to be sensitively enhanced with shortening interaction range and suppressed by the correlation effect.

    DOI: 10.1016/S0379-6779(98)00654-7

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  • Geometry, universality and dimensional crossovers in weakly coupled one-dimensional conductors Reviewed

    J Kishine, K Yonemitsu

    SYNTHETIC METALS   103 ( 1-3 )   2650 - 2650   1999.6

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    We discuss dimensional crossover phenomena in weakly coupled one-dimensional conductors, in terms of the universality classes of the corresponding isolated one-dimensional systems.

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  • Berry phases and pairing symmetry in Holstein-Hubbard polaron systems Reviewed

    K Yonemitsu, J Zhong, HB Schuttler

    PHYSICAL REVIEW B   59 ( 2 )   1444 - 1467   1999.1

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    We study the tunneling dynamics of dopant-induced hole polarons that are self-localized by electron-phonon coupling in a two-dimensional antiferromagnet. Our treatment is based on a path-integral formulation of the adiabatic (Born-Oppenheimer) approximation, combined with many-body tight-binding, instanton, constrained lattice dynamics, and many-body exact diagonalization techniques. The applicability and limitations of the adiabatic approximation in polaron tunneling problems are discussed in detail and adiabatic results are compared to exact numerical results for a two-site polaron problem. Our results are mainly based on the Holstein-tJ and? for comparison, on the Holstein-Hubbard model. We also study the effects of second-neighbor hopping and long-range electron-electron Coulomb repulsion. The polaron tunneling dynamics is mapped onto an effective low-energy Hamiltonian that takes the form of a fermion tight-binding model with occupancy-dependent, predominantly second- and third-neighbor tunneling matrix elements, excluded double occupancy, and effective intersite charge interactions. Antiferromagnetic spin correlations in the original many-electron Hamiltonian are reflected by an attractive contribution to the first-neighbor charge interaction and by Berry phase factors that determine the signs of effective polaron tunneling matrix elements. In the two-polaron case, these phase factors lead to polaron-pair wave functions of either d(x2-y2)-wave symmetry or p-wave symmetry with zero and nonzero total pair momentum, respectively. Implications for the doping-dependent isotope effect, pseudogap, and T-c of a superconducting polaron-pair condensate are discussed and compared to observed properties of the cuprate high-T-c materials. [S0163-1829(99)04602-0].

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  • Localized vibrational modes of excitation in electroluminescent polymers Reviewed

    H Jiang, XH Xu, Sun, X, K Yonemitsu

    CHINESE PHYSICS LETTERS   16 ( 11 )   836 - 837   1999

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    The localized vibrational modes of exciton and polaron are investigated, and the results show that the frequencies of the three even parity modes of exciton are very different from those of polaron. For the exciton, three modes are distinctly separated; but, for the polaron, two modes with higher frequencies are close to each other, Then, it is possible to distinguish exciton from polaron by watching their Roman spectra. Therefore, the localized mode may be used to specify the exciton and polaron in the electroluminescent polymers.

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  • Theoretical study on electron correlation of 1-D (DCNQI)(2)M (M = Li, Ag) salts Reviewed

    Y Imamura, S Ten-no, K Yonemitsu, Y Tanimura

    CHEMICAL PHYSICS LETTERS   298 ( 1-3 )   15 - 20   1998.12

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    We study electronic states of the (DCNQI)(2)M (M = Li and Ag) salts based on the full configuration interaction (FCI) method using effective Hamiltonians derived from ab initio molecular orbital theory. FCI results of the DCNQI tetramer and octamer models indicate that the ground state has antiferromagnetic and charge ordering correlations. It corresponds to the 2k(F) spin density wave and 4k(F) charge density wave states (SDW and CDW, respectively). In the octamer model, it is also found that some low-lying excited states have similar spin-flipped CDW correlations and the antiferromagnetic correlation is weakened. (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0009-2614(98)01212-3

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  • Off-diagonal interactions and spin-density waves in polymers Reviewed

    XH Xu, RT Fu, K Hu, Sun, X, K Yonemitsu

    PHYSICAL REVIEW B   58 ( 14 )   9039 - 9046   1998.10

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    In order to clarify the effects of electron interactions on the competition between SDW (spin-density wave) and BOW (bond-order wave). the existing theories are improved in two aspects: (1) The electron interaction in polymers. which possess a broadband. is described by a screened Coulomb potential rather than the extended Hubbard model, which is a good approximation only for narrow-band systems. (2) A spin-dependent correlated-basis-function method is developed to calculate the correlation effect, which goes beyond the Hartree-Fock approximation, Our study shows that the off-diagonal interaction substantially influences the competition so that shortening of the interaction range greatly enhances the SDW: meanwhile the correlation effect promotes the BOW against the SDW. [S0163-1829(98)00537-2].

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  • Antiferromagnetic phase transition and crossover to Fermi liquid phase in a weakly coupled half-filled chain system Reviewed

    J Kishine, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   67 ( 8 )   2590 - 2593   1998.8

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    Effects of the intrachain electron-electron umklapp process and the interchain one-particle hopping, II, in a weakly coupled half-filled chain system have been studied, based on the perturbative renormalization-group approach. By solving the scaling equations, we found that the intrachain umklapp process strongly suppresses an interchain one-particle process and causes a finite critical value for t(perpendicular to), t(perpendicular to c). For t(perpendicular to) &lt; t(perpendicular to c), as the temperature decreases, the system undergoes a phase transition into an antiferromagnetic long-range-ordered phase at a transition temperature T-N which increases with the increasing t(perpendicular to). On the other hand, for t(perpendicular to) &gt; t(perpendicular to c), the system undergoes a crossover to the Fermi liquid phase where the interchain coherent propagation of quasi-particles occurs.

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  • Dimensional crossovers in the doped ladder system: Spill gap, superconductivity and interladder coherent band motion Reviewed

    J Kishine, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   67 ( 5 )   1714 - 1731   1998.5

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    Based on the perturbative renormalization group (PRG) approach, we have studied dimensional crossovers in Hubbard ladders coupled via weak interladder one-particle hopping, t(perpendicular to). found that the one-particle crossover is strongly suppressed through growth of the intraladder scattering processes which lead the isolated Hubbard ladder system toward the spin gap metal (SGM) phase. Consequently when t(perpendicular to) sets in, there exists, for any finite intraladder Hubbard repulsion, U &gt; 0, the region where the two-particle crossover dominates the one-particle crossover and consequently the d-wave superconducting transition, which is regarded as a bipolaron condensation, occurs. By solving the scaling equations for the interladder one-particle and two-particle hopping amplitudes, we give phase diagrams of the system with respect to U, t(perpendicular to 0) (initial value of t(perpendicular to)) and the temperature, T. We compared the above dimensional crossovers with those in a weakly coupled chain system: clarifying the difference between them.

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  • Coexistence of SDW and purely-electronic CDW in quarter-filled organic conductors Reviewed

    N Kobayashi, M Ogata, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   67 ( 4 )   1098 - 1101   1998.4

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    We have performed a mean field calculation in order to determine the ground state of a modified Hubbard model of a quarter-filled one-dimensional chain. It is found that the coexistence of 2k(F) spin density wave (SDW) and purely-electronic 2k(F) charge density wave (CDW) is realized due to the effect of next-nearest-neighbor Coulomb repulsion. Phase diagrams are obtained as the values of nearest-and next-nearest-neighbor Coulomb interaction energies are varied. Competition between the two coexistent states with 2k(F) CDW and 4k(F) CDW is revealed, which gives a first order transition. Our result supports the X-ray result confirming the presence of a coexisting phase of purely-electronic 2k(F) CDW and 2k(F) SDW in (TMTSF)(2)PF6, a quarter-filled one-dimensional chain in terms of holes.

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  • Effect of electron correlation on competition between BOW and SDW in polymer Reviewed

    Sun, X, XH Xu, K Hu, K Yonemitsu

    PHYSICS LETTERS A   239 ( 3 )   191 - 195   1998.3

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    Because pi electrons in polymers possess a broad band, the off-diagonal part of the electron interaction, which is omitted in the extended Hubbard model, plays an essential role in the competition between bond-order waves (BOWs) and spin-density waves (SDWs). Our study, which goes beyond the extended Hubbard model and the Hartree-Fock approximation, shows that this competition depends on the range of the electron interaction; a short interaction range, where the off-diagonal part is more effective, is in favor of SDW. It is also shown that the correlation effect works against the exchange effect in building up the SDW. (C) 1998 Published by Elsevier Science B.V.

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  • Superconductivity and Magnetism in Quasi-One-Dimensional Two-Band Systems Reviewed

    K. Yonemitsu, J. Kishine, T. Ogawa

    Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu   7   490 - 492   1998

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    We study crossovers from one to quasi-one dimensions in doped two-leg ladder systems, using a renormalization group method. When quasi-one dimensionality is regarded as controlled by incomplete interference between the Cooper and Peierls channels, we obtain spin-density wave, d-wave superconductor, and metallic phases with decreasing dominance of the Peierls channel. When transverse single-particle hopping is treated perturbationally, we obtain a one-particle crossover from incoherent to coherent transverse motion for weak interaction and a two-particle crossover from short- to long-range ordering of a d-wave superconductor for strong interaction. We also study a magnetic property in a doped Heisenberg-Kondo chain, using the exact diagonalization method. A fully saturated ferromagnetism in the ferromagnetic Kondo chain is destroyed by rather weak antiferromagnetic Heisenberg coupling between localized 5=1/2 spins. [doped ladder, pair tunneling, dimensional crossover, Heisenberg-Kondo lattice, ferromagnetic Kondo model]. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.

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  • On the Effects of On-Site Coulomb Interaction in Strongly Dimerized Two Band Systems

    H. Kino, T. Miyazaki, M. Mori, K. Yonemitsu

    Proceedings of the JRCAT Conference   1998

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  • Spin gap and superconductivity in weakly coupled ladders: Interladder one-particle vs. two-particle crossover Reviewed

    J Kishine, K Yonemitsu

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   66 ( 12 )   3725 - 3728   1997.12

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    Effects of the interladder one-particle hopping, t(perpendicular to), on the low-energy asymptotics of a weakly coupled Hubbard ladder system have been studied, based on the perturbative renormalization-group approach. We found that for finite intraladder Hubbard repulsion, U, there exists a crossover value of the interladder one-particle hopping, t(perpendicular to c). For 0 &lt; t(perpendicular to) &lt; t(perpendicular to c), the spin gap metal (SGM) phase of the isolated ladder transits at a finite transition temperature, T-c, to the d-wave superconducting (SCd) phase via a two-particle crossover. In the temperature region, T &lt; T-c, interladder coherent Josephson tunneling of the Cooper pairs occurs, while the interladder coherent one-particle process is strongly suppressed. For tie &lt; tl, around a crossover temperature, T-cross, the system crosses over to the two-dimensional (2D) phase via a one-particle crossover. In the temperature region, T &lt; T-cross, the interladder coherent band motion occurs.

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  • Renormalization-group approach to the metal-insulator transitions in (DCNQI)(2)M (DCNQI is N,N&apos;-dicyanoquinonediimine and M=Ag, Cu) Reviewed

    K Yonemitsu

    PHYSICAL REVIEW B   56 ( 12 )   7262 - 7276   1997.9

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    Metal-insulator transitions and different ground-state phases in the quasi-one-dimensional materials, (R1R2-DCNQI)(2)M (R-1 = R-2 = CH3, I and M = Ag, Cu), are studied with a renormalization-group method. We use one-dimensional continuum models with backward scatterings, umklapp processes, and couplings with 2k(F) and 4k(F) phonons (not static lattice distortion). We take a quarter-filled band for M = Ag and a sixth-filled band coupled with a third-filled band for M = Cu. Depending on electron-electron and electron-phonon coupling strengths, the ground-state phase becomes a Tomonaga-Luttinger liquid or a state with a gap(s). For M = Ag, there appears a spin-gap state with a dominant 2k(F) charge-density-wave correlation, a Mott insulator with a dominant 4k(F) charge-density-wave correlation, or a spin-Peierls state with different magnitudes of spin and charge gaps. Three dimensionality is taken into account by cutting off the logarithmic singularity in either the particle-particle channel or the particle-hole channel. The difference between the ground-state phase of the R-1 = R-2 = CH3 salt (spin-Peierls state) and that of the R-1 = R-2 = I salt (antiferromagnetic state) is qualitatively I explained by a difference in the cutoff energy in the particle-particle channel. For M = Cu, there appears a Mott insulator with a charge-density wave of period 3 and a Peierls insulator with a charge-ensity wave of period 6. The conditions for the experimentally observed, Mott insulator phase are strong correlation in the sixth-filled band, moderate electron-phonon couplings, and finite electron-4k(F) phonon coupling. Resistance is calculated as a function of temperature with a memory-function approximation in both cases above. It qualitatively reproduces the differences among the M = Ag and M = Cu cases as well as the R-1 = R-2 = CH3 and R-1 = R-2 = I cases.

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  • Phonon effects on superconducting phase in two-chain electron systems Reviewed

    K Yonemitsu

    PHYSICA C   282 ( Pt.2 )   1109 - 1110   1997.8

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    The scaling shows that superconductivity in a two-leg ladder is easily broken by couplings with 2k(F) and 4k(F) phonons at quarter filling. Three-dimensionality makes the system an antiferromagnet if the nesting is still perfect.

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  • Quasi-particle band structure and gapless superconductivity in the vortex-lattice state Reviewed

    T Nishio, K Yonemitsu, H Ebisawa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   66 ( 4 )   953 - 956   1997.4

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    The quasi-particle spectrum for s-wave superconductors in the Vortex-lattice state remains gapless in magnetic fields much below the upper critical field H-c2 where the cyclotron frequency is smaller than the amplitude of the pair potential. This is shown through self-consistent solutions of the Bogoliubov-de Gennes equations for the attractive Hubbard model on the square lattice. It has not been predicted in earlier theoretical works based on a continuous model because it is due to the dispersion of Landau subbands in the lattice model.

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  • Mott transition in quasi-one-dimensional electron systems of quarter filling Reviewed

    K. Yonemitsu

    Synthetic Metals   85 ( 1/3 )   1635 - 1636   1997.3

  • Various Transitions in Quasi-One-Dimensional Systems under High Pressure

    K. Yonemitsu, J. Kishine, T. Ogawa

    Special Issue of The Review of High Pressure Science and Technology   6   360   1997

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  • Electron-phonon interaction and spin gap in nearly-half-filled correlated electron systems Reviewed

    K. Yonemitsu, M. Imada

    Physica C: Superconductivity and its Applications   263 ( 1-4 )   82 - 85   1996.5

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    Renormalization-group equations are solved to study phase diagrams of nearly-half-filled one-dimensional conductors interacting with phonons. A spin-gap charge density wave phase exists between a gapless density wave phase and a spin-gap superconductor phase. On-site and intersite electron-phonon couplings show large differences near half-filling in the presence of on-site electron repulsion.

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  • Spin gap in one-dimensional electron-phonon systems Reviewed

    Kenji Yonemitsu, Masatoshi Imada

    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals   285-286   223 - 228   1996

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    The exponents of spin and charge correlations of one-dimensional electron systems are calculated by a renormalization-group method. We study combined effects of electron-phonon interaction and the Umklapp process on renormalization flows. As scattering processes are successively integrated out, these two processes are interfered with each other depending on the type of electron-phonon coupling, phonon frequency and filling. We demonstrate how these factors control a spin gap formation and density-wave/superconductor correlations.

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  • Spin-gap phase in nearly half-filled one-dimensional conductors coupled with phonons Reviewed

    K. Yonemitsu, M. Imada

    Physical Review B - Condensed Matter and Materials Physics   54 ( 4 )   2410 - 2420   1996

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    Asymptotic properties of nearly half-filled one-dimensional conductors coupled with phonons are studied through a renormalization-group method. Due to spin-charge coupling via an electron-phonon interaction, the spin correlation varies with filling as well as the charge correlation. Depending on the relation between cutoff energy scales of the umklapp process and of the electron-phonon interaction, various phases appear. We find a metallic phase with a spin gap and a dominant charge-density-wave correlation near half filling between a gapless density-wave phase (like in the doped repulsive Hubbard model) and a superconductor phase with a spin gap. The spin gap is produced by phonon-assisted backward scatterings that interfere with the umklapp process constructively or destructively depending on the character of electron-phonon coupling. © 1996 The American Physical Society.

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  • BERRY PHASES, PAIRING SYMMETRY, AND NODELESS D-WAVE STATES IN A STRONGLY CORRELATED POLARON MODEL Reviewed

    HB SCHUTTLER, K YONEMITSU, J ZHONG

    JOURNAL OF SUPERCONDUCTIVITY   8 ( 5 )   555 - 558   1995.10

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    We use path integral and exact diagonalization techniques to study the tunneling of dopant-induced hole polarons which are self-localized by electron-phonon coupling in a two-dimensional anti-ferromagnet, Their low-energy dynamics is found to be dominated by 2nd and 3rd neighbor hopping processes which carry a (-1) Berry phase factor and lead to non-s-wave hole pairing symmetries, including possible nodeless d(x2-y2) pair wavefunctions. The nodeless The polarons obey effective spin-1/2-fermion quasi-particle statistics. d(x2-y2)-wave pairing state can exhibit a transition from gapless to fully gapped behavior in its quasi-particle excitation spectrum, without change of pairing symmetry.

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  • CONTINUUM-LIMIT OF THE FLUCTUATION FACTOR IN COHERENT-STATE FUNCTIONAL-INTEGRALS FOR TRANSITION AMPLITUDES Reviewed

    K YONEMITSU

    PHYSICAL REVIEW A   50 ( 6 )   5324 - 5327   1994.12

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  • Time-dependent mean-field theory for tunneling in electron-phonon systems Reviewed

    K. Yonemitsu

    Physical Review B   50 ( 5 )   2899 - 2920   1994.8

  • INSTABILITY OF VORTEX TEXTURES IN THE 2-DIMENSIONAL HUBBARD-MODEL Reviewed

    K YONEMITSU, AR BISHOP

    PHYSICAL REVIEW B   48 ( 9 )   6680 - 6682   1993.9

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    The Hubbard model on a two-dimensional square lattice is investigated within an unrestricted, inhomogeneous Hartree-Fock approximation. Vortexlike states discussed by Verges et al. [Phys. Rev. B 43, 6099 (1991)] are studied in detail. They are found to be unstable against transverse spin fluctuations. Doping of holes does not suppress these fluctuations strongly enough to stabilize the vortex states.

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  • OPTICAL-EXCITATIONS ALONG CUO CHAINS IN COPPER OXIDES Reviewed

    K YONEMITSU, AR BISHOP

    PHYSICAL REVIEW B   48 ( 5 )   3349 - 3355   1993.8

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    Optical responses in a one-dimensional two-band Peierls-Hubbard model near 5/8 filling (i.e., near 1/4 filling in the effective one-band model) are studied within inhomogeneous Hartree-Fock and random-phase approximations. Low-energy collective excitations are produced by a sliding motion of a spin-density wave. In the commensurate case (i.e., at 5/8 filling) or near this filling with moderate strength of intersite electron-lattice coupling, the spin-density wave (with polaronic defects in the latter case) is pinned by commensurability with the lattice, and the lowest-frequency optical response lies in the infrared regime. Otherwise, the spin-density wave is incommensurate and moves freely unless it is pinned by extrinsic impurities. Implications for midinfrared absorptions observed in YBa2Cu3O7 and PrBa2Cu3O7 compounds are discussed. With sufficiently weak hopping between the Cu and O sites, a ferromagnetic phase is found.

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  • DYNAMIC AND STATIC CORRELATION-FUNCTIONS IN THE INHOMOGENEOUS-HARTREE-FOCK-STATE APPROACH WITH RANDOM-PHASE-APPROXIMATION FLUCTUATIONS Reviewed

    J LORENZANA, MD GRYNBERG, L YU, K YONEMITSU, AR BISHOP

    PHYSICAL REVIEW B   47 ( 20 )   13156 - 13163   1993.5

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    The ground-state energy and static and dynamic correlation functions are investigated in the inhomogeneous-Hartree-Fock (IHF) plus random-phase-approximation (RPA) approach applied to a one-dimensional spinless-fermion model showing self-trapped doping states at the mean-field level. Results are compared with those obtained using homogeneous HF and exact diagonalization. RPA fluctuations added to the generally inhomogeneous-HF ground state allow the computation of dynamical correlation functions that compare well with exact diagonalization results. The RPA correction to the ground-state energy agrees well with the exact results at strong- and weak-coupling limits. We also compare it with a related quasiboson approach. The instability towards self-trapped behavior is signaled by a RPA mode with frequency approaching zero.

    DOI: 10.1103/PhysRevB.47.13156

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  • DOPING STATES IN THE 2-DIMENSIONAL 3-BAND PEIERLS-HUBBARD MODEL Reviewed

    K YONEMITSU, AR BISHOP, J LORENZANA

    PHYSICAL REVIEW B   47 ( 18 )   12059 - 12088   1993.5

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    Doping states in a two-dimensional three-band Peierls-Hubbard model for the copper oxides are investigated with inhomogeneous Hartree-Fock (HF) and random-phase approximations. The doping states are sensitive to small changes of interaction parameters because they easily change local energy balance between different interactions around added holes. For the parameter values derived from constrained-density-functional methods for the copper oxides, added holes form isolated small ferromagnetic polarons. When the parameters are varied around these values, different types of doping states are obtained: For stronger on-site repulsion at Cu sites, larger ferromagnetic polarons are formed, which are qualitatively different from the small polarons; for stronger nearest-neighbor Cu-O repulsion, polarons are clumped or there occurs phase separation into Cu- and O-hole-rich regions; intersite electron-lattice coupling rapidly changes the small polarons by quenching a Cu magnetic moment and locally distorting the lattice in an otherwise undistorted antiferromagnetic background. This is regarded as a rapid crossover from a Zhang-Rice singlet to a covalent molecular singlet, and occurs substantially below a critical strength for destruction of the stoichiometric antiferromagnetic state. However intrasite electron-lattice coupling, in contrast to the intersite coupling, does not dramatically affect the hole-doping states. Doping induces modes in magnetic, optical, and vibronic response functions. Local infrared-active phonon modes are induced in infrared absorption spectra for finite electron-lattice coupling. They are correlated with doping-induced particle-hole excitations observed in optical absorption spectra and in magnetic excitation spectra. These doping-induced particle-hole excitations are associated with the local HF eigenstates in the charge-transfer gap. Each doping state has distinctive excitation spectra in the magnetic, optical, and vibronic channels. In particular, the hole-doping states with small polarons have doping-induced, infrared absorption peaks on the low-frequency side of the stoichiometric peak, while the electron-doping states have them on the high-frequency side.

    DOI: 10.1103/PhysRevB.47.12059

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  • ELECTRON-PHONON DRIVEN SPIN FRUSTRATION IN MULTIBAND HUBBARD MODELS - MX CHAINS AND OXIDE SUPERCONDUCTORS Reviewed

    JT GAMMEL, K YONEMITSU, A SAXENA, AR BISHOP, H RODER

    SYNTHETIC METALS   56 ( 2-3 )   3377 - 3382   1993.4

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    We discuss the consequences of both electron-phonon and electron-electron couplings in 1D an 2D multi-band (Peierls-Hubbard) models. After briefly discussing various analytic limits, we focus on (Hartree-Fock and exact) numerical studies in the intermediate regime for both couplings, where unusual spin-Peierls as well as long-period, frustrated ground states are found. Doping into such phases or near the phase boundaries can lead to further interesting phenomena such as separation of spin and charge, a dopant-induced phase transition of the global (parent) phase, or real-space (''bipolaronic'') pairing. We discuss possible experimentally observable consequences of this rich phase diagram for halogen-bridged, transition metal, linear chain complexes (MX chains) in 1D and the oxide superconductors in 2D.

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  • MAGNETISM AND COVALENCY IN THE 2-DIMENSIONAL 3-BAND PEIERLS-HUBBARD MODEL Reviewed

    K YONEMITSU, AR BISHOP, J LORENZANA

    PHYSICAL REVIEW B   47 ( 13 )   8065 - 8075   1993.4

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    Stoichiometric phases and doping states are studied in a two-dimensional, three-band extended Peierls-Hubbard model, using an inhomogeneous Hartree-Fock approximation. Magnetism and covalency are investigated in a parameter space of strong intersite electron-lattice coupling and varying on-site electron-electron repulsion strength. In a crossover region between a charge-density-wave phase driven by intersite electron-lattice coupling and an antiferromagnetic phase driven by on-site electron-electron repulsion, a bond-order-wave state, a spin-Peierls state, and a mixed state of spin-Peierls bonds and antiferromagnetic spins axe found to be stable and caused by competing magnetism and covalency of different relative strengths. Doping states depend qualitatively upon the nature of these global phases. In particular, separation of spin and charge is observed in the background of the bond-order-wave state as a consequence of local competition between magnetism and covalency.

    DOI: 10.1103/PhysRevB.47.8065

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  • Linear Excitations around Broken-Symmetry Mean-Field States: Doping States in the Copper Oxides Reviewed

    K. Yonemitsu, A. R. Bishop, J. Lorenzana

    Modern Physics Letters B   7 ( 6 )   355 - 377   1993.3

  • VIBRONIC, OPTICAL, AND MAGNETIC EXCITATIONS AROUND SOLITONS IN A ONE-DIMENSIONAL 2-BAND PEIERLS-HUBBARD MODEL Reviewed

    K YONEMITSU, AR BISHOP

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   ( 113 )   155 - 165   1993

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    Nonlinear doping states in a charge-density-wave background and those in a spin-density-wave background are investigated through their response functions in vibronic, optical and magnetic channels in a one-dimensional two-band Peierls-Hubbard model. A random phase approximation is used for their analysis on the basis of totally unrestricted Hartree-Fock solutions. Doping-induced changes of excitation spectra in these different channels are distinctive to the nature of individual doping states.

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  • SENSITIVITY OF DOPING STATES IN THE COPPER OXIDES TO ELECTRON-LATTICE COUPLING Reviewed

    K YONEMITSU, AR BISHOP, J LORENZANA

    PHYSICAL REVIEW LETTERS   69 ( 6 )   965 - 968   1992.8

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    Doping states in a two-dimensional three-band Peierls-Hubbard model are investigated with inhomogeneous Hartree-Fock and random phase approximations. They are sensitive to small changes of electron-lattice and electron-electron interactions. For parameters relevant to the insulating copper oxides a small ferromagnetic polaron is found. Moderate intersite electron-lattice coupling triggers a nonlinear feedback mechanism resulting in a rapid crossover from a Zhang-Rice regime to a covalent molecular singlet state in which the local magnetic moment is quenched and local lattice distortion is large. Various states are characterized by distinct optical and infrared absorption spectra.

    DOI: 10.1103/PhysRevLett.69.965

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  • RANDOM-PHASE-APPROXIMATION APPROACH TO OPTICAL AND MAGNETIC EXCITATIONS IN THE 2-DIMENSIONAL MULTIBAND HUBBARD-MODEL Reviewed

    K YONEMITSU, AR BISHOP

    PHYSICAL REVIEW B   45 ( 10 )   5530 - 5534   1992.3

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    As a convenient qualitative approach to strongly correlated electronic systems, an inhomogeneous Hartree-Fock plus random-phase approximation is applied to response functions for the two-dimensional multiband Hubbard model for cuprate superconductors. A comparison of the results with those obtained by exact diagonalization by Wagner, Hanke, and Scalapino [Phys. Rev. B 43, 10 517 (1991)] shows that overall structures in optical and magnetic particle-hole excitation spectra are well reproduced by this method. This approach is computationally simple, retains conceptual clarity, and can be calibrated by comparison with exact results on small systems. Most importantly, it is easily extended to larger systems and straightforward to incorporate additional terms in the Hamiltonian, such as electron-phonon interactions, which may play a crucial role in high-temperature superconductivity.

    DOI: 10.1103/PhysRevB.45.5530

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  • RANDOM-PHASE-APPROXIMATION APPROACH TO COLLECTIVE MODES AROUND INHOMOGENEOUS HARTREE-FOCK STATES - ONE-DIMENSIONAL DOPED HUBBARD-MODEL Reviewed

    K YONEMITSU, BATISTIC, I, AR BISHOP

    PHYSICAL REVIEW B   44 ( 6 )   2652 - 2663   1991.8

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    All the linear excitations are calculated in the random-phase approximation around a doped inhomogeneous Hartree-Fock state as well as the undoped uniform antiferromagnetic state in the one-dimensional Hubbard model. Upon doping, shape modes appear, localized around an introduced hole, as well as some "shake-off" branches related to combinations of local and extended Hartree-Fock orbitals. These modes are in addition to spin wave and ultragap branches in the pure antiferromagnetic state. Some characteristics of the shape modes are similar to bare processes in the t-t'-J model derived from the Hubbard model at strong coupling. Spectral weights in different susceptibility channels are calculated and shown to have peaks in low-energy regions, arising from specific shape modes.

    DOI: 10.1103/PhysRevB.44.2652

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  • SPIN FLUCTUATIONS AND SUPERCONDUCTIVITY IN 2-DIMENSIONAL CUO2 SYSTEM Reviewed

    K YONEMITSU

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   59 ( 6 )   2183 - 2204   1990.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PHYSICAL SOCIETY JAPAN KIKAI-SHINKO BUILDING  

    DOI: 10.1143/JPSJ.59.2183

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  • VERTEX CORRECTION TO RPA AND SUPERCONDUCTIVITY IN THE 2-DIMENSIONAL HUBBARD-MODEL Reviewed

    K YONEMITSU

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   58 ( 12 )   4576 - 4599   1989.12

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    DOI: 10.1143/JPSJ.58.4576

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  • ANISOTROPY IN ELECTRON-PHONON INTERACTIONS AND SUPERCONDUCTING TRANSITION IN A TWO-DIMENSIONAL SYSTEM Reviewed

    K YONEMITSU, Y WADA

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   58 ( 9 )   3304 - 3323   1989.9

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    DOI: 10.1143/JPSJ.58.3304

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  • CORRELATION-EFFECTS ON THE SPIN SOLITON IN POLYACETYLENE Reviewed

    K YONEMITSU, Y ONO, Y WADA

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   57 ( 11 )   3875 - 3886   1988.11

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    DOI: 10.1143/JPSJ.57.3875

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  • CORRELATION-EFFECTS ON THE PHONONS LOCALIZED AROUND A SOLITON OR A POLARON IN POLYACETYLENE Reviewed

    K YONEMITSU, Y ONO, Y WADA

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   56 ( 12 )   4400 - 4407   1987.12

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    DOI: 10.1143/JPSJ.56.4400

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Books

  • Handbook of Quantum Light-Matter Interactions

    ( Role: Contributor)

    2023.3  ( ISBN:9784860438265

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    Total pages:3, 8, 933, 13p, 図版31p   Language:Japanese  

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  • Opto-magneto effect and ultrafast charge dynamics in α-RuCl3

    T. Amano, Y. Kawakami, H. Itoh, S. Iwai, K. Yonemitsu

    kotai butsuri, Vol. 57, No. 11, 667-679  2022.11 

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  • Petahertz Current Control by Nearly Single-Cycle Light Pulse in an Organic Superconductor

    S. Iwai, Y. Kawakami, H. Itoh, K. Yonemitsu

    The Review of Laser Engineering, Vol. 50, No. 6, 313-317 (2022).  2022.6 

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  • Petahertz Correlated Electron Dynamics in an Organic Superconductor

    S. Iwai, Y. Kawakami, H. Itoh, K. Yonemitsu

    2022.5 

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  • Spontaneous Formation of Correlated Charge Coherence Induced by 1.5-Cycle Pulse in 1-D Organic Metal (TMTTF)$_2$AsF$_6$

    T. Ishikawa, Y. Sagae, Y. Naito, J. Ichimura, Y. Kawakami, H. Itoh, K. Yamamoto, K. Yakushi, S. Ishihara, T. Sasaki, K. Yonemitsu, S. Iwai

    Ultrafast Phenomena XIX, edited by K. Yamanouchi, S. Cundiff, R. de Vivie-Riedle, M. Kuwata-Gonokami, L. DiMauro (Springer Proceedings in Physics, Vol. 162) pp. 244-247  2015.1 

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  • 光誘起電荷秩序融解のしくみ

    米満 賢治

    パリティ, Vol. 29, No. 07, 55-59  2014.7 

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  • Theory of MMX-Chain Compounds

    K. Yonemitsu

    Material Designs and New Physical Properties in MX- and MMX-Chain Compounds, edited by M. Yamashita and H. Okamoto (Springer-Verlag, Wien) pp.243-264  2013.1 

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  • 相関電子系を有する分子性結晶の光誘起相転移―理論的アプローチ―

    米満 賢治

    固体物理, Vol. 48, No. 1, 1-12  2013.1 

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  • Theory of photoinduced phase transitions in quasi-one-dimensional organic conductors

    Molecular Electronic and Related Materials -- Control and Probe with Light, edited by T. Naito (Research Signpost/Transworld Research Network, Trivandrum, India) 305-320  2010  ( ISBN:9788178954608

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  • Theory of photoinduced phase transitions in quasi-one-dimensional organic conductors

    K. Yonemitsu

    Molecular Electronic and Related Materials -- Control and Probe with Light, edited by T. Naito (Research Signpost/Transworld Research Network, Trivandrum, India) 305-320  2010  ( ISBN:9788178954608

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  • 理論が解き明かす光誘起相転移

    Chemistry & Chemical Industry, Vol. 62, No. 8, 892-894  2009 

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  • 理論が解き明かす光誘起相転移

    米満賢治

    化学と工業, Vol. 62, No. 8, 892-894  2009 

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  • Theory of Photoinduced Phase Transitions: Coherent Oscillations and Transient States

    The Review of Laser Engineering (in Japanese), Vol. 36, No.6, 343-348  2008 

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  • 光誘起相転移の理論-コヒーレント振動と過渡状態-

    米満賢治

    レーザー研究, Vol. 36, No.6, 343-348  2008 

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  • Theory of Optical Responses of Photoexcited Halogen-Bridged Metal Complexes in Different Insulating Phases (共著)

    Multifunctional Conducting Molecular Materials, edited by G. Saito, F. Wudl, R. C. Haddon, K. Tanigaki, T. Enoki, H. E. Katz and M. Maesato (RSC Publishing, Cambridge)  2007 

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  • 光で電子を一斉に動かし物性を変えるしくみの理論

    米満賢治

    光アライアンス, Vol. 18, No.7, 29-33  2007 

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  • Mechanism of Ambipolar Field-Effect Transistors on One-Dimensional Organic Mott Insulators

    K. Yonemitsu

    Multifunctional Conducting Molecular Materials, edited by G. Saito, F. Wudl, R. C. Haddon, K. Tanigaki, T. Enoki, H. E. Katz and M. Maesato (RSC Publishing, Cambridge)  2007 

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  • Theory of Optical Responses of Photoexcited Halogen-Bridged Metal Complexes in Different Insulating Phases

    N. Maeshima, K. Yonemitsu

    Multifunctional Conducting Molecular Materials, edited by G. Saito, F. Wudl, R. C. Haddon, K. Tanigaki, T. Enoki, H. E. Katz and M. Maesato (RSC Publishing, Cambridge)  2007 

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  • Theory about Mechanism of Transferring Many Electrons at Once and Changing Material Properties by Photoexcitations

    Optical Alliance (in Japanese), 18, 29-33  2007 

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  • Mechanism of Ambipolar Field-Effect Transistors on One-Dimensional Organic Mott Insulators

    Multifunctional Conducting Molecular Materials, edited by G. Saito, F. Wudl, R. C. Haddon, K. Tanigaki, T. Enoki, H. E. Katz and M. Maesato (RSC Publishing, Cambridge)  2007 

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  • Theory of optical phase control in charge-transfer complexes

    Proceeding of International Conference on Science and Technology of Synthetic Metals (ICSM2004), University of Wollongong, Intelligent Polymer Research Institute, Australia  2004 

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  • Theory of optical phase control in charge-transfer complexes

    K. Yonemitsu

    Proceeding of International Conference on Science and Technology of Synthetic Metals (ICSM2004), University of Wollongong, Intelligent Polymer Research Institute, Australia  2004 

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  • Inter-chain electrostriction and pressure-induced multicriticality in charge transfer organic complexes (共著)

    Proceeding of International Conference on Science and Technology of Synthetic Metals (ICSM2004), University of Wollongong, Intelligent Polymer Research Institute, Australia  2004 

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  • Inter-chain electrostriction and pressure-induced multicriticality in charge transfer organic complexes

    J. Kishine, T. Luty, K. Yonemitsu

    Proceeding of International Conference on Science and Technology of Synthetic Metals (ICSM2004), University of Wollongong, Intelligent Polymer Research Institute, Australia  2004 

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  • 低次元金属錯体の多様な電子物性の起源

    米満賢治

    「集積型金属錯体の科学」(化学同人)Ⅱ部 12章  2003 

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  • 低次元金属錯体の多様な電子物性の起源

    「集積型金属錯体の科学」(化学同人)Ⅱ部 12章  2003 

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  • Spin Solitons in the Alternate Charge Polarization Background of MMX Chains

    M. Kuwabara, K. Yonemitsu, H. Ohta

    EPR in the 21st Century, edited by Kawamori, J. Yamauchi and H. Ohta  2002 

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  • Spin Solitons in the Alternate Charge Polarization Background of MMX Chains (共著)

    EPR in the 21st Century, edited by Kawamori, J. Yamauchi and H. Ohta  2002 

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  • Two-loop renormalization of the quasiparticle weight in two-dimensional electron systems (共著)

    International Journal of Modern Physics B  2001 

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  • Charge Ordering and Optical Conductivity of MMX Chains

    M. Kuwabara, K. Yonemitsu

    Physics in Local Lattice Distortions  2001 

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  • Two-loop renormalization of the quasiparticle weight in two-dimensional electron systems

    J. Kishine, N. Furukawa, K. Yonemitsu

    International Journal of Modern Physics B  2001 

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  • Charge Ordering and Optical Conductivity of MMX Chains (共著)

    Physics in Local Lattice Distortions  2001 

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  • One-Particle vs. Two-Particle Crossover in Weakly Coupled Hubbard Chains and Ladders : Perturbative Renormalization Group Approach(共著)

    Recent Progress in Many-Body Theories  1998 

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  • One-Particle vs. Two-Particle Crossover in Weakly Coupled Hubbard Chains and Ladders : Perturbative Renormalization Group Approach

    J. Kishine, K. Yonemitsu

    Recent Progress in Many-Body Theories  1998 

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  • LOCAL VIBRONIC AND ELECTRONIC EXCITATIONS OF DOPING-INDUCED STATES IN THE COPPER OXIDES

    Manifestations of the Electron-Phonon Interaction in High-Tc Superconductivity  1995 

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  • Local Vibronic and Electronic Excitations of Doping-Induced States in the Copper Oxides

    K. Yonemitsu, A. R. Bisho, J. Lorenzana

    Manifestations of the Electron-Phonon Interaction in High-Tc Superconductivity  1995 

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  • FORMATION OF SOLITON VAND IN ONE-DIMENSIONAL PEIERLS-HUBBARD MODEL

    Nonilinear Coherent Structures in Physics and Bioligy  1994 

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  • Formation of Soliton Band in One-Dimensional Peierls-Hubbard Model

    K. Yonemitsu

    Nonilinear Coherent Structures in Physics and Bioligy  1994 

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  • Infrared Absorption Spectra of Various Doping States in Cuprate Superconductors

    K. Yonemitsu, A. R. Bisho, J. Lorenzana

    Lattice Dffects in High-Tc Superconductors  1992 

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  • INFRARED ABSORPTION SPECTRA OF VARIOUS DOPING STATES IN CUPRATE SUPERCONDUCTORS

    Lattice Dffects in High-Tc Superconductors  1992 

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  • RPA, VERTEX CORRECTION AND SUPERCONDUCTIVITY IN TWO-DIMENSIONAL MODELS

    Strongly Coupled Plasma Physics  1990 

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  • RPA, Vertex Correction and Superconductivity in Two-Dimensional Models

    K. Yonemitsu

    Strongly Coupled Plasma Physics  1990 

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MISC

  • Petahertz driving of charge motion in strongly correlated systems

    岩井伸一郎, 天野辰哉, 川上洋平, 伊藤弘毅, 米満賢治

    応用物理学会春季学術講演会講演予稿集(CD-ROM)   70th   2023

  • Ultrafast magneto-optical responses of spin-orbit assisted Mott insulator α-RuCl3

    天野辰哉, 川上洋平, 伊藤弘毅, 今野克哉, 青山拓也, 今井良宗, 大串研也, 若林裕助, 後藤貫太, 中村優斗, 岸田英夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   77 ( 1 )   2022

  • ダイナミクスと新奇物性 α-RuCl3における光磁気効果と超高速電荷ダイナミクス

    天野辰哉, 川上洋平, 伊藤弘毅, 岩井伸一郎, 米満賢治

    固体物理   57 ( 11 )   2022

  • Ultrafast magneto-optical responses of spin-orbit assisted Mott insulator α-RuCl3: II

    天野辰哉, 川上洋平, 伊藤弘毅, 今野克哉, 青山拓也, 今井良宗, 大串研也, 若林裕助, 後藤貫太, 中村優斗, 岸田英夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   77 ( 2 )   2022

  • 6-fs SHG spectroscopy in an electronic ferroelectric α-(ET)2I3

    川上洋平, 天野辰哉, 伊藤弘毅, 山本薫, 中村優斗, 岸田英夫, 佐々木孝彦, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   77 ( 1 )   2022

  • Ultrafast spin dynamics of Kitaev spin liquid candidate α-RuCl3: III

    天野辰哉, 大橋拓純, 川上洋平, 伊藤弘毅, 今野克哉, 青山拓也, 今井良宗, 大串研也, 若林裕助, 後藤貫太, 中村優斗, 岸田英夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   76 ( 1 )   2021

  • Ultrafast spin dynamics of Kitaev spin liquid candidate α-RuCl3: II

    天野辰哉, 赤嶺勇人, 大橋拓純, 川上洋平, 伊藤弘毅, 今野克哉, 長谷川慶直, 佐々木宏也, 青山拓也, 今井良宗, 大串研也, 若林裕助, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   75 ( 1 )   2020

  • Second and third harmonic generations driven by a strong light field of a 6 fs single-cycle infrared pulse in an organic superconductor: II

    川上洋平, 天野辰哉, 伊藤弘毅, 川口玄太, 山本浩史, 中村優斗, 岸田英夫, 佐々木孝彦, 石原純夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   75 ( 1 )   2020

  • 6fs単一サイクル光強電場による有機超伝導体の非線形電荷振動 III

    川上洋平, 天野辰哉, 赤嶺勇人, 伊藤弘毅, 川口玄太, 山本浩史, 岸田英夫, 佐々木孝彦, 石原純夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   74 ( 1 )   2019

  • 単一サイクル光強電場が駆動する有機超伝導体の非線形電荷振動

    川上洋平, 天野辰哉, 伊藤弘毅, 川口玄太, 山本浩史, 岸田英夫, 伊藤桂介, 佐々木孝彦, 石原純夫, 田中康寛, 米満賢治, 岩井伸一郎

    応用物理学会秋季学術講演会講演予稿集(CD-ROM)   80th   2019

  • 6fs単一サイクル近赤外パルスによる有機超伝導体の第2,第3高調波発生

    川上洋平, 天野辰哉, 伊藤弘毅, 岸田英夫, 佐々木孝彦, 石原純夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   74 ( 2 )   2019

  • Photoinduced charge-order melting triggered by 6 fs single-cycle infrared pulses in α-(ET)2I3 II; Changes of reflectivity and SHG intensity

    Akamine Y, Yonemitsu K, Iwai S, Amano T, Kawakami Y, Itoh H, Yamamoto K, Nakamura Y, Kishida H, Sasaki T, Ishihara S

    Meeting Abstracts of the Physical Society of Japan   73 ( 0 )   1550 - 1550   2018

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  • 6fs単一サイクル光強電場による有機超伝導体の非線形電荷振動 II

    川上洋平, 天野辰哉, 米山雄登, 赤嶺勇人, 伊藤弘毅, 川口玄太, 山本浩史, 岸田英夫, 伊藤桂介, 佐々木孝彦, 石原純夫, 田中康寛, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   73 ( 2 )   2018

  • 6fs単一サイクル赤外光による有機超伝導体の非線形電荷振動

    川上洋平, 天野辰哉, 米山雄登, 赤嶺勇人, 伊藤弘毅, 川口玄太, 山本浩史, 岸田英夫, 伊藤桂介, 佐々木孝彦, 石原純夫, 田中康寛, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   73 ( 1 )   2018

  • 6fs単一サイクル赤外光によるα‐(ET)2I3の電荷秩序融解

    川上洋平, 天野辰哉, 米山雄登, 伊藤弘毅, 山本薫, 中村優斗, 岸田英夫, 佐々木孝彦, 石原純夫, 米満賢治, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   72 ( 2 )   ROMBUNNO.22pB21‐2   2017.9

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  • Polarization analysis of light-field induced charge-localization in triangular-latticed organic conductor

    Amano T, Tanaka Y, Yonemitsu K, Iwai S, Yoneyama Y, Kawakami Y, Itoh H, Yamamoto K, Nakamura Y, Kishida H, Sasaki T, Ishihara S

    Meeting Abstracts of the Physical Society of Japan   72 ( 0 )   1425 - 1425   2017

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    &lt;p&gt;三角格子構造の二次元有機伝導体alpha-(ET)2I3の光強電場誘起の電荷局在を7 fs近赤外光によって明らかにしてきた、今回は、7 fsプローブパルスの偏光を変え、局在電荷状態の異方性を明らかにする。また、ポンプ光による印加電場の偏光方向に対して、電荷局在の効率がどのように変わるのかを調べ、厳密対角化に基ずく理論計算との比較から、光誘起電荷局在の機構を議論する。&lt;/p&gt;

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  • 6fs単一サイクル赤外光によって生成されるκ型ET塩のドレスト電子状態

    米山雄登, 天野辰哉, 川上洋平, 伊藤弘毅, 米山直樹, 伊藤桂介, 佐々木孝彦, 米満賢治, 石原純夫, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   72 ( 2 )   2017

  • κ型ET塩の金属-モット絶縁体相境界における超高速臨界現象 III

    米山雄登, 川上洋平, 天野辰哉, 加藤隆寛, 伊藤弘毅, 米山直樹, 佐々木孝彦, 米満賢治, 石原純夫, 岩井伸一郎

    日本物理学会講演概要集(CD-ROM)   72 ( 1 )   2017

  • 19aCF-4 Ultrafast dynamics of strong electric field effects in (TMTTF)_2AsF_6

    Naitoh Y, Iwai S, Kawakami K, Ishikawa T, Kato T, Itoh H, Yamamoto K, Sasaki T, Tanaka Y, Yonemitsu K

    Meeting Abstracts of the Physical Society of Japan   70 ( 0 )   1351 - 1351   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_1351

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  • ダイマー結晶における光誘起電荷秩序融解のパルス光強度・形状依存性

    西岡圭太, 米満賢治

    日本物理学会講演概要集(CD-ROM)   70 ( 1 )   2015

  • 対称モノサイクル光パルス励起による負温度状態生成と相互作用反転

    米満賢治, 西岡圭太

    日本物理学会講演概要集(CD-ROM)   70 ( 1 )   2015

  • 19aCF-7 larization dependence of photoinduced charge localization in charge ordered organic conductor

    Ishikawa T, Ishihara S, Tanaka Y, Yonemitsu K, Iwai S, Naitoh Y, Kato T, Kawakami Y, Itoh H, Yamamoto K, Nakamura Y, Kishida H, Sasaki T

    Meeting Abstracts of the Physical Society of Japan   70 ( 0 )   1354 - 1354   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_1354

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  • 22pCP-10 Correlated charge dynamics driven by 1.5-cycle infrared pulse : electronic ferroelectrics α-(ET)_2I_3 IV

    Ishikawa T, Sasaki T, Ishihara S, Tanaka Y, Yonemitsu K, Iwai S, Sagae Y, Naitoh Y, Kawakami Y, Itoh H, Yamamoto K, Yakushi K, Nakamura Y, Kishida H

    Meeting Abstracts of the Physical Society of Japan   70 ( 0 )   1522 - 1522   2015

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    DOI: 10.11316/jpsgaiyo.70.1.0_1522

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  • 8aAD-2 Ultrafast electronic dynamics driven by 1.5-cycle IR pulse laser : electronic ferroelectrics (TMTTF)_2AsF_6 II

    Sagae Y., Ishikawa T., Naitoh Y., Kawakami Y., Itoh H., Yamamoto K., Yakushi K., Sasaki T., Ishihara S., Yonemitsu K., Iwai S.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   510 - 510   2014.8

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  • 光誘起電荷秩序融解のしくみ

    米満 賢治

    パリティ   29 ( 7 )   55 - 59   2014.7

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  • Photoinduced insulating of layered organic metal driven by strong electric field of 1.5-cycle, 7 fs infrared pulse

    S. Iwai, T. Ishikawa, Y. Sagae, Y. Naito, J. Ichimura, Y. Kawakami, H. Itoh, S. Ishihara, K. Yamamoto, K. Yakushi, T. Sasaki, H. Kishida, K. Yonemitsu

    Optics InfoBase Conference Papers   2014.1

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    Photoinduced metal to insulator (M-I) change were realized by strong electric filed (10 MV/cm) of 1.5-cycle (7 fs) near infrared pulse. Threshold for the M-I change decrease near the M-I transition temperature. The M-I change is driven by coherent charge oscillation with a period of 20 fs. © 2014 OSA.

    DOI: 10.1364/up.2014.09.wed.p3.40

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  • 8aAD-4 Correlated charge dynamics driven by 1.5-cycle infrared pulse : electronic ferroelectrics α-(ET)_2I_3 III

    Kawakami Y, Sasaki T, Ishihara S, Tanaka Y, Yonemitsu K, Iwai S, Ishikawa T, Sagae Y, Naitoh Y, Itoh H, Yamamoto K, Yakushi K, Nakamura Y, Kishida H

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   510 - 510   2014

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  • 27pAS-2 Correlated charge dynamics driven by 1.5-cycle infrared pulse : electronic ferroelectrics α-(ET)_2I_3

    Ishikawa T, Iwai S, Yamada K, Sagae Y, Itoh H, Yamamoto K, Yakushi K, Sasaki T, Ishihara S, Yonemitsu K

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   731 - 731   2014

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  • 27pAS-1 Correlated charge dynamics driven by 1.5-cycle infrared pulse : electronic ferroelectrics (TMTTF)_2AsF_6

    Sagae Y, Ishikawa T, Yamada K, Itoh H, Yamamoto K, Yakushi K, Ishihara S, Yonemitsu K, Iwai S

    Meeting Abstracts of the Physical Society of Japan   69 ( 0 )   731 - 731   2014

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  • ダイマー結晶における光誘起ダイマー間電荷移動の連続光/パルス光による制御

    西岡圭太, 西岡圭太, 米満賢治, 米満賢治

    日本物理学会講演概要集   69 ( 1 )   2014

  • Numerical calculation of photoinduced nonequilibrium phonons in electron-hole-phonon coupled system and frequency modulation in perturbative representation

    Nishioka Keita, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   68 ( 2 )   677 - 677   2013.8

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  • Photoinduced phase transitions in molecular crystals as correlated electron systems : Theoretical approach

    48 ( 1 )   1 - 12   2013.1

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  • 20pPSB-63 Melting of charge order by electric field and nonlinear conduction in two-dimensional organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   571 - 571   2012.8

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  • Material designs and new physical properties in MX-and MMX-Chain compounds

    Masahiro Yamashita, Hiroshi Okamoto, Hiroaki Iguchi, Kaoru Iwano, Hideo Kishida, Hiroyuki Matsuzaki, Minoru Mitsumi, Arao Nakamura, Shinya Takaishi, Kenji Yonemitsu

    Material Designs and New Physical Properties in MX- and MMX-Chain Compounds   9783709113172   1 - 270   2012.6

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    This is the first book to comprehensively address the recent developments in both the experimental and theoretical aspects of quasi-one-dimensional halogen-bridged mono- (MX) and binuclear metal (MMX) chain complexes of Pt, Pd and Ni. These complexes have one-dimensional electronic structures, which cause the various physical properties as well as electronic structures. In most MX-chain complexes, the Pt and Pd units are in M(II)-M(IV) mixed valence or charge density wave (CDW) states due to electron-phonon interactions, and Ni compounds are in Ni(III) averaged valence or Mott-Hubbard states due to the on-site Coulomb repulsion. More recently, Pd(III) Mott-Hubbard (MH) states have been realized in the ground state by using the chemical pressure. Pt and Pd chain complexes undergo photo-induced phase transitions from CDW to MH or metal states, and Ni chain complexes undergo photo-induced phase transitions from MH to metal states. Ni chain complexes with strong electron correlations show tremendous third-order optical nonlinearity and nonlinear electrical conductivities. They can be explained theoretically by using the extended Peierls-Hubbard model. For MMX-chain complexes, averaged valence, CDW, charge polarization, and alternating charge polarization states have been realized by using chemical modification and external stimuli, such as temperature, photo-irradiation, pressure, and water vapor. All of the electronic structures and phase transitions can be explained theoretically.

    DOI: 10.1007/978-3-7091-1317-2

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  • 25pBL-6 Theory of Many-Electron-Phonon Correlations during Photoinduced Phase Transitions

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   808 - 808   2012.3

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  • 26pBK-8 Charge order and nonlinear conduction in organic conductor β-(meso-DMBEDT-TTF)_2PF_6

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   908 - 908   2012.3

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  • 量子化磁場下におけるビスマスナノワイヤのNernst効果:ワイヤ径と温度依存性

    平山尚美, 遠藤彰, 白崎良演, 中村浩章, 長谷川靖洋, 羽田野直道, 藤田和博, 米満賢治

    日本物理学会講演概要集   67 ( 2 )   2012

  • Et2Me2Sb[Pd(dmit)2]2における光誘起電荷秩序融解ダイナクス

    西岡圭太, 米満賢治, 米満賢治, 米満賢治

    日本物理学会講演概要集   67 ( 1 )   2012

  • 22aTC-2 Roles of Lattice Phonons and Molecular Vibrations during Photoinduced Neutral-Ionic Transitions

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   756 - 756   2011.8

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  • 21aTR-8 Theory of nonlinear conduction and charge older with structural distention in quasi-two-dimensional organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   842 - 842   2011.8

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  • 25pHC-6 Role of Intramolecular Vibrations on Neutral-Ionic Transitions Revealed by Photoinduced Dynamics

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   744 - 744   2011.3

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  • 26pPSA-13 Theory of nonlinear conduction for charge-ordered states in θ-type organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   621 - 621   2011.3

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  • ビスマスナノワイヤーの量子化磁場下での熱電特性の理論計算

    平山尚美, 遠藤彰, 藤田和博, 長谷川靖洋, 羽田野直道, 中村浩章, 白崎良演, 米満賢治

    日本物理学会講演概要集   66 ( 2 )   2011

  • Et2Me2Sb[Pd(dmit)2]2における電荷分離相の光誘起融解ダイナミクス

    西岡圭太, 米満賢治

    日本物理学会講演概要集   66 ( 2 )   2011

  • Et2Me2Sb[Pd(dmit)2]2における電荷分離相の光誘起融解の理論

    西岡圭太, 米満賢治

    金属dmit錯体による磁性・伝導性研究の最前線 理研シンポジウム 平成23年   2011

  • 擬一次元スピン軌道相互作用系の熱電効果における量子振動

    中村浩章, 白崎良演, 羽田野直道, 米満賢治, 平山尚美

    日本物理学会講演概要集   66 ( 1 )   2011

  • 電流加熱時の磁場中極低温2次元電子系の冷却効果

    平山尚美, 遠藤彰, 藤田和博, 長谷川靖洋, 羽田野直道, 中村浩章, 白崎良演, 米満賢治

    日本物理学会講演概要集   66 ( 1 )   2011

  • Et2Me2Sb[Pd(dmit)2]2における電荷分離相の光誘起融解の理論

    西岡圭太, 米満賢治

    日本物理学会講演概要集   66 ( 1 )   2011

  • 26aRB-13 Theory of nonlinear conduction for charge-ordered systems on a triangular lattice

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   830 - 830   2010.8

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  • 26aRB-12 Nonequilibrium states and current-voltage characteristics of a one-dimensional Hubbard model attached to electrodes

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   830 - 830   2010.8

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  • 21pHQ-10 Growth dynamics of photoinduced domains in two-dimensional charge-ordered organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   768 - 768   2010.3

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  • 光に誘起された電子状態変化に対する異なる理論的アプローチ(研究会「相関電子系における光誘起現象」報告,研究会報告)

    米満 賢治

    物性研究   94 ( 2 )   224 - 224   2010

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    Other Link: https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=474585

  • 二次元有機導体における電荷秩序の光誘起融解の理論(研究会「相関電子系における光誘起現象」報告,研究会報告)

    田中 康寛, 米満 賢治

    物性研究   94 ( 2 )   222 - 222   2010

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    Other Link: https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=474583

  • 25aXA-5 Photoinduced dynamics in two-dimensional organic conductors : the cases of α-,θ-, andκ-type ET salts

    Miyashita S., Tanaka Y., Iwai S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   609 - 609   2009.8

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  • 25pYC-7 Theory of nonequilibrium steady state under electric current in two-dimensional charge-ordered systems

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   737 - 737   2009.8

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  • 28pVD-5 Photoinduced dynamics in two-dimensional organic conductors

    Miyashita S., Tanaka Y., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   734 - 734   2009.3

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  • 30aYG-12 Suppression of Rectification at Metal-Mott-Insulator Interfaces : Nonequilibrium Green's-Function Approach

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   858 - 858   2009.3

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  • 21pYD-1 Photoinduced melting of charge order in quasi-two-dimensional organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   643 - 643   2008.8

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  • 23aYH-9 Charge order with lattice distortion and its photoinduced melting in quasi two-dimensional organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   63 ( 1 )   693 - 693   2008.2

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  • 24aTF-10 Effects of electron-phonon couplings on charge orders in θ-type and α-type ET salts : Approach from the strong-coupling limit

    Miyashita S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   63 ( 1 )   813 - 813   2008.2

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  • 23aYH-1 Energy Transfer to Phonons after Photoexcitation in 1D Correlated E-Ph Systems

    Yonemitsu Kenji, Maeshima Nobuya

    Meeting abstracts of the Physical Society of Japan   63 ( 1 )   691 - 691   2008.2

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  • 22aTK-13Transient Spectra during Photo induced Melting of Charge Order in ID E-Ph Systems

    Yonemitsu Kenji, Maeshima Nobuya

    Meeting abstracts of the Physical Society of Japan   62 ( 2 )   742 - 742   2007.8

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  • 23pPSB-4 Analysis of polaron states in one-dimensional dimerized Mott insulators

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   62 ( 2 )   774 - 774   2007.8

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  • 21aPS-16 Release of charge flustration due to lattice distortions in quasi-two-dimensional organic conductors

    Miyashita S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   62 ( 2 )   522 - 522   2007.8

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  • 22aTK-9 Photoirradiation effects on charge order in α-(ET)_2I_3

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   62 ( 2 )   741 - 741   2007.8

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  • 光で電子を一斉に動かし物性を変えるしくみの理論--遍歴電子系の光誘起相転移ダイナミクスにおける電子相関の役割

    米満 賢治

    光アライアンス   18 ( 7 )   29 - 33   2007.7

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  • 20pZB-7 CT Processes, Phonon Modes and Efficiency in Photoinduced Melting of Charge Order

    Yonemitsu Kenji, Maeshima Nobuya

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   748 - 748   2007.2

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  • 20pZB-4 Lattice-effect differences between the charge ordering in θ-RhZn salt and that in α-I_3 salt

    Miyashita S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   748 - 748   2007.2

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  • 21aRA-9 Effects of electron-lattice coupling on charge order in quasi two-dimensional organic conductors

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   856 - 856   2007.2

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  • 20pZB-15 The lowest photoexcited state of dimerized one-dimensional Mott insulators

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   750 - 750   2007.2

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  • 20aRA-10 Effect of quantum phonon fluctuations near the neutral-ionic Quantum critical point

    Yamashita Yasufumi, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   841 - 841   2007.2

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  • 25pYF-12 Optical conductivity of charge-ordered ET salts at 1/4-filling; Importance of lattice distortions

    Miyashita S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   700 - 700   2006.8

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  • 23pQE-12 Photoinduced dynamics of dimerized one-dimensional Mott insulators II

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   572 - 572   2006.8

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  • 24pRA-5 Photoinduced Phase Transition Dynamics Depending on Electron Correlations in Organic Semiconductors

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   591 - 591   2006.8

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  • 25pYF-2 Mean field study of the effects of electron-lattice coupling on charge order in θ-(ET)_2X

    Tanaka Yasuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   697 - 697   2006.8

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  • 28aPS-47 Photoinduced dynamics of dimerized one-dimensional Mott insulators

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   735 - 735   2006.3

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  • 28pTD-9 Quantum Paraelectricity near the Neutral-Ionic Quantum Critical Points

    Yamashita Yasufumi, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   837 - 837   2006.3

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  • 29pUB-2 Carrier Transport through Molecular Semiconductor/Metal Interfaces (Theory)

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   842 - 842   2006.3

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  • 27pRB-11 Effects of electron-phonon interactions on the charge ordering in θ-type ET salts

    Miyashita S., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   811 - 811   2006.3

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  • 22pWB-9 Effects of Interchain Interactions on Photo induced Ionic-Neutral Phase Transitions

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   719 - 719   2005.8

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  • 20aYD-14 Photoinduced dynamics in one-dimensional Mott and band insulators

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   581 - 581   2005.8

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  • 25aYR-7 Quantum Ising model coupled with conducting electrons

    Yamashita Yasufumi, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   905 - 905   2005.3

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  • 26pYK-15 Field Effects on 1D Mott Insulators : Origin of the Ambipolar IV Characteristics

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   805 - 805   2005.3

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  • 27aXQ-3Optical responses of photoexcited states in the 1D ionic-Hubbard model

    Maeshima N., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   722 - 722   2005.3

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  • 13aWH-2 Relaxation process in neutral-ionic, paraelectric-ferroelectric phase transition of TTF-CA

    Inoue Hitoshi, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   59 ( 2 )   750 - 750   2004.8

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  • 28pWG-8 Double Pulse and Interference in Photoinduced Ionic-Neutral Phase Transitions

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   59 ( 1 )   847 - 847   2004.3

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  • Ferroelectric phase transition, ionicity condensation, and multicriticality in charge transfer organic complexes

    Kishine J., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   58 ( 2 )   757 - 757   2003.8

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  • Pulse Electric Field Dependence of Photoinduced Ionic-Neutral Phase Transitions

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   58 ( 2 )   757 - 757   2003.8

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  • Multicritical behavior in the charge-transfer complex TTF-CA : Analysis based on the Q1D Blume-Emery-Griffiths model

    Kishine J., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   58 ( 1 )   779 - 779   2003.3

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  • Competition between I-I solitons and N-I domain walls in photoinduced ionic-to neutral phase transition : Excitation intensity and degree of initial lattice disorder dependability

    Miyashita Naoyuki, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   58 ( 1 )   676 - 676   2003.3

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  • Two-step photo-induced phase transitions in a two-sublattice model

    Otsuka Y., Yonemitsu K.

    Meeting abstracts of the Physical Society of Japan   58 ( 1 )   688 - 688   2003.3

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  • Dimerization disordering and coupled charge-lattice dynamics after photoexcitations in a one-dimensional extended Peierls-Hubbard model.

    Miyashita Naoyuki, Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   57 ( 2 )   644 - 644   2002.8

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  • Quantum Fluctuations and Coherence Recovery in the Photoinduccd Charge-Density-Wave-to-Charge-Polarization Phase Transition in MMX-Chain Compounds

    Yonemitsu Kenji, Miyashita Naoyuki, Kuwabara Makoto

    Meeting abstracts of the Physical Society of Japan   57 ( 2 )   709 - 709   2002.8

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  • 24aYD-13 Domain dynamics after photoexcitations in a one-dimensional Peierls-Hubbard model II.

    Miyashita Naoyuki, Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   57 ( 1 )   663 - 663   2002.3

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  • 25pXM-5 Lattice Instability and Excitation Spectra around Neutral-Ionic Phase I ansitioneby the finite-T DMRG Method

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   57 ( 1 )   781 - 781   2002.3

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  • Quantum Fluctuations, Thermal Fluctuations and Lattice Instability in Neutral-Ionic Phase Transitions at Finite Temperatures

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 2 )   688 - 688   2001.9

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  • Incommensurate States near Mott Transition to Three-Fold Charge Ordering State

    Kuwabara Makoto, Yonemitsu Kenji, Ohta Hitoshi

    Meeting abstracts of the Physical Society of Japan   56 ( 2 )   699 - 699   2001.9

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  • Domain dynamics after photoexcitations in a one-dimensional Peierls-Hubbard model

    Miyashita Naoyuki, Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 2 )   610 - 610   2001.9

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  • Charge/Lattice Ordering and Optical Responses of Halogen-Bridged Binuclear Metal Complexes (MMX)

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 1 )   682 - 682   2001.3

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  • Optical Conductivities of Dimerized Two-Band Systems and θ-ET Salts

    Mori Michiyasu, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 1 )   780 - 780   2001.3

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  • Self-Doping and Mott Transition to Three-Fold Charge Ordering State

    Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 1 )   780 - 780   2001.3

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  • Spectra near Quantum Phase Transitions in Quasi-One-Dimensional Conductors

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   56 ( 1 )   775 - 775   2001.3

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  • Excitation Spectra of Quasi-One-Dimensional Conductors : Spinless Case

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   55 ( 2 )   700 - 700   2000.9

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  • Charge Ordering Patterns and Collective Excitation Spectra in θ-(BEDT-TTF) Salts

    Mori Michiyasu, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   55 ( 2 )   708 - 708   2000.9

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  • Charge ordering and absorption spectra in MMX chains

    Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   55 ( 2 )   743 - 743   2000.9

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  • Charge Ordering Patterns and Excitation Spectra

    Mori Michiyasu, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   55 ( 1 )   702 - 702   2000.3

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  • Charge ordcring and effects of p-d coupling in MMX chains

    Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   55 ( 1 )   744 - 744   2000.3

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  • d=1+ε連続次元ハーフフィリング電子系の量子相転移と電荷ギャップ崩壊

    岸根順一郎, 米満賢治

    日本物理学会講演概要集   54 ( 2 )   727 - 727   1999.9

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  • 26aE-1 Electron Correlation in Low-Dimensional Dimerized Conductors, : Pd(dmit)_2 Salts and MMX-Chain Complexes

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   54 ( 2 )   759 - 759   1999.9

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  • 擬1次元電子系の量子揺らぎと次元性が引き起こす相転移とクロスオーバー

    岸根順一郎, 米満賢治

    物性研だより   39 ( 2 )   34 - 35   1999.7

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  • 28a-XB-9 Antiferromagnet-SDW Transition in Quasi-One-Dimensional Organic Conductors

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   54 ( 1 )   242 - 242   1999.3

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  • 30-p-XB-1 Numerical studies of the ground state phase diagram for MMX chain

    Kuwabara Makoto, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   54 ( 1 )   264 - 264   1999.3

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  • 29a-XB-2 Theoretical study of electronic properties of k-BEDT-TTF salts.

    Imamura Y., Ten-no S., Yonemitsu K., Tanimura Y.

    Meeting abstracts of the Physical Society of Japan   54 ( 1 )   251 - 251   1999.3

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  • モット転移とアンダーソン局在の競合に対する次元性効果

    岸根順一郎, 米満賢治

    日本物理学会講演概要集   54 ( 1 )   675 - 675   1999.3

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  • 部分的に平坦なフェルミ面を持つ2次元電子系の低エネルギー漸近挙動 準粒子ウエイト繰り込みの異方的流れ

    岸根順一郎, 米満賢治

    日本物理学会講演概要集   53 ( 2 )   613 - 613   1998.9

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  • Magnetic properties and Conductivity of CoPc(AsF_6)_<0.5>II

    OGAWA Takuhiro, YONEMITSU Kenji

    Meeting abstracts of the Physical Society of Japan   53 ( 2 )   326 - 326   1998.9

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  • Effective Exchange Interaction in Dimerized Systems

    MORI Michiyasu, YONEMITSU Kenji, KINO Hiori

    Meeting abstracts of the Physical Society of Japan   53 ( 2 )   291 - 291   1998.9

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  • 1p-PSA-54 Magnetic and Orderings in Strongly Dimerized Two Band Systems.

    KINO H., MIYAZAKI T., MORI M., YONEMITSU K.

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   445 - 445   1998.3

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  • Polaron Paring and Its Symmetry in the Strong Antiferromagnetic Background Institute for Molecular Science

    YONEMITSU Kenji

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   231 - 231   1998.3

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  • 2p-YX-6 How to Make a Molecule with Negative Polarizability? : A New Photoinduced Phenomenon

    SUN Xin, YONEMITSU Kenji

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   271 - 271   1998.3

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  • Pressure and Interaction Effects for Ground State Properties of Pd(dmit)_2 Salts

    MORI Michiyasu, YONEMITSU Kenji

    Meeting abstracts of the Physical Society of Japan   53 ( 1 )   246 - 246   1998.3

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  • Dimensional Crossovers in Strongly Correlated Low-dimensional Systems.

    岸根順一郎, 米満賢治

    日本物理学会講演概要集(年会)   53 ( 1 )   245   1998.3

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  • 5p-C-11 Magnetic properties and Conductivity of CoPc(AsF_6)_0.5

    Ogawa Takuhiro, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   52 ( 2 )   271 - 271   1997.9

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  • 6p-C-11 Metal-Insulator Transition in 2-Bands Systems of 1 and 2 Dimension

    Mori Michiyasu, Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   52 ( 2 )   283 - 283   1997.9

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  • 6p-C-12 Dimensionality and Phonon Effects on Superconductivity in a Two-Band System

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   52 ( 2 )   284 - 284   1997.9

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  • Superconducting Instability in Doped Ladder System: Interladder Pair Tunneling and Dimensionality Crossover.

    岸根順一郎, 米満賢治

    日本物理学会講演概要集(分科会)   1997   601   1997.9

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  • 29p-C-5 Renormalization-Group Approach to Metal-Insulator Transition in (DCNQI)_2Cu

    Yonemitsu Kenji

    Meeting abstracts of the Physical Society of Japan   52 ( 1 )   276 - 276   1997.3

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  • Vortex states of on-site attractive Hubbard model and extended Hubbard model by mean field approximation

    Nishio T., Yonemitsu K., Ebisawa H.

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 3 )   480 - 480   1996.9

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  • Interference of the Umklapp process with electron-phonon interaction in 1D 1/4-filled electron systems

    YONEMITSU Kenji

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 2 )   415 - 415   1996.9

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  • de Haas-van Alphen Oscillations of Attractive Hubberd Model

    SATO Jun, NISHIO Takayuki, YONEMITSU Kenji, EBISAWA Hiromichi

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1996 ( 3 )   378 - 378   1996.9

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  • 2p-YD-9 Vortex states of Attractive Hubbard Model by Mean Field Approximation

    Nishio T., Yonemitsu K., Ebisawa H.

    Abstracts of the meeting of the Physical Society of Japan. Annual meeting   51 ( 3 )   466 - 466   1996.3

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  • 30p-K-10 Scaling in Nearly-Half-Filled One-Dimensional Electron-Phonon Systems

    YONEMITSU Kenji

    Abstracts of the meeting of the Physical Society of Japan. Sectional meeting   1995 ( 2 )   422 - 422   1995.9

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  • Berry Phases and the Symmetry of Hole Pairs in the Holstein-tJ Model

    Yonemitsu K., Zhong J., Schuttler H.-B.

    Abstracts of the meeting of the Physical Society of Japan. Annual meeting   50 ( 3 )   354 - 354   1995.3

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  • 3a-ZB-12 Spin Fluctuation and Superconductivity in the Two-Dimensional CuO_2 Plane

    Yonemitsu Kenji

    1989 ( 3 )   225 - 225   1989.9

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  • 28p-SC-13 Vertex Correction for a Superconducting State in the Hubbard Model

    Yonemitsu Kenji

    44 ( 3 )   183 - 183   1989.3

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  • 28a-QB-3 ポリアセチレンにおけるソリトンおよびポーラロンとフォノン : 電子相関の効果

    米満 賢治, 小野 嘉之

    秋の分科会講演予稿集   1986 ( 3 )   337 - 337   1986.9

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Presentations

  • Spin Hall effect and anomalous Hall effect of transition-metal dichalcogenides driven by circularly polarized light

    Naoya Arakawa, Kenji Yonemitsu

    JPS 2024 Spring Meeting  2024.3 

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  • Valley degree of freedom and anomalous Hall effect in graphene driven by bicircularly polarized light

    Naoya Arakawa, Kenji Yonemitsu

    JPS 2024 Spring Meeting  2024.3 

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  • Ultrafast dynamics of photoinduced disorder in an electronic ferroelectric α-(ET)2I3

    Y. Kawakami, T. Amano, H. Itoh, K. Yamamoto, Y. Nakamura, H. Kishida, T. Sasaki, K. Yonemitsu, S. Iwai

    JPS Annual (78th) Meeting  2023.9 

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  • Light-induced mirror symmetry breaking and charge transport

    Naoya Arakawa, Kenji Yonemitsu

    JPS Annual (78th) Meeting  2023.9 

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  • Spin Hall and anomalous Hall effects of a multiorbital metal driven by bicircularly polarized light

    Naoya Arakawa, Kenji Yonemitsu

    JPS 2023 Spring Meeting  2023.3 

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  • 超伝導体、強相関電子系におけるペタヘルツ電子駆動 Invited

    岩井 伸一郎, 天野 辰哉, 川上 洋平, 伊藤 弘毅, 米満 賢治

    第70回応用物理学会春季学術講演会  2023.3 

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    Event date: 2023.3    

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  • スピン軌道モット絶縁体α-RuCl3の光誘起磁化ダイナミクス Invited

    米満賢治

    研究会 ―相関電子の軌道自由度から生まれる多様性と普遍性―  2022.10 

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  • Synchronized Charge Oscillations in Conductors with Dimer Structures

    Kenji Yonemitsu

    The 14th International Symposium on Crystalline Organic Metals, Superconductors and Magnets (ISCOM2022)  2022.9 

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  • Spin Hall effect and anomalous Hall effect of a photo-irradiated multiorbital metal

    Naoya Arakawa, Kenji Yonemitsu

    JPS 2022 Autumn Meeting  2022.9 

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  • Ultrafast magneto-optical responses of spin-orbit assisted Mott insulator α-RuCl3 II

    T. Amano, Y. Kawakami, H. Itoh, K. Konno, T. Aoyama, Y. Imai, K. Ohgushi, Y. Wakabayashi, K. Goto, Y. Nakamura, H. Kishida, K. Yonemitsu, S. Iwai

    JPS 2022 Autumn Meeting  2022.9 

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  • Oscillating charge order and spin polarization in photoexcited Mott insulators Invited

    K. Yonemitsu

    International School and Workshop on Electronic Crystals (ECRYS-2022)  2022.8 

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  • Nonlinear charge oscillations and second harmonic generation in organic conductors with dimerized structures

    K. Yonemitsu

    International Conference on Science and Technology of Synthetic Metals (ICSM2022)  2022.7 

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  • 6-fs SHG spectroscopy in an electronic ferroelectric α-(ET)2I3

    Y. Kawakami, T. Amano, H. Itoh, K. Yamamoto, Y. Nakamura, H. Kishida, T. Sasaki, K. Yonemitsu, S. Iwai

    JPS Annual (77th) Meeting  2022.3 

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  • Ultrafast magneto-optical responses of spin-orbit assisted Mott insulator α-RuCl3

    T. Amano, Y. Kawakami, H. Itoh, K. Konno, T. Aoyama, Y. Imai, K. Ohgushi, Y. Wakabayashi, K. Goto, Y. Nakamura, H. Kishida, K. Yonemitsu, S. Iwai

    JPS Annual (77th) Meeting  2022.3 

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  • Photoinduced Magnetization Dynamics in a Three-Orbital Hubbard Model for α-RuCl3

    Kenji Yonemitsu

    JPS Annual (77th) Meeting  2022.3 

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  • Ultrafast spin/charge dynamics in quantum-spin materials: Symmetry aspects Invited

    K. Yonemitsu

    The 7th International Conference on Photoinduced Phase Transitions and Cooperative Phenomena (PIPT7)  2021.11 

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    Event date: 2021.11    

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  • Mechanism for Synchronization of Charge Oscillations in Dimer Lattices

    Kenji Yonemitsu, Philipp Werner

    JPS 2021 Autumn Meeting  2021.9 

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  • Photoinduced Charge Oscillations in Dimerized Organic Conductors International conference

    K. Yonemitsu

    The 13th International Symposium on Crystalline Organic Metals, Superconductors and Magnets (ISCOM2019)  2019.9  Tomar, Portugal

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  • Synchronized charge oscillation after a strong optical electric field is applied to superconductors with dimerized crystal structures

    K. Yonemitsu

    Gordon Research Conference on Conductivity & Magnetism in Molecular Materials  2018.8  Smithfield, RI, USA

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  • Conditions for Photoinduced Enhancement/Suppression of Orders: Charge Order and Excitonic Condensation

    K. Yonemitsu

    International School and Workshop on Electronic Crystals, ECRYS-2017  2017.8  Cargese, France

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  • Photoinduced Interaction Modulation and Charge Localization: Order Formed in a Quasi-Two-Dimensional Organic Conductor

    K. Yonemitsui

    International Research School: Electronic States and Phases Induced by Electric or Optical Impacts (IMPACT 2016)  2016.8  Cargese, France

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  • Charge orders induced by strong optical electric field and anisotropic transfers/ interactions

    K. Yonemitsu

    Gordon Research Conference on Conductivity & Magnetism in Molecular Materials  2016.8  South Hadley, MA, USA

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  • Ultrafast optical response of the metallic phase of α-(ET)2I3 induced by 7 fs infrared pulse

    T. Ishikawa, Y. Naitoh, Y. Kawakami, H. Itoh, K. Yamamoto, K. Yakushi, H. Kishida, T. Sasaki, S. Ishihara, Y. Tanaka, K. Yonemitsu, S. Iwai

    The 11th International Symposium on Crystalline Organic Metals Superconductors and Magnets (ISCOM2015)  2015.9  Bad G\"ogging, Germany

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  • Negative-Temperature State and Phase Separation Induced by Symmetric Monocycle Optical Pulse in Extended Hubbard Models

    K. Yonemitsu, Y. Tanaka, H. Yanagiya

    The 11th International Symposium on Crystalline Organic Metals Superconductors and Magnets (ISCOM2015)  2015.9  Bad G\"ogging, Germany

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  • Optical Control of Charge Transfers Using Molecular Hierarchy and Photoinduced Charge-Order Melting

    K. Yonemitsu, K. Nishioka

    International Conference on Science and Technology of Synthetic Metals 2014 (ICSM 2014)  2014.7 

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  • Pulsed vs. CW Laser Excitations: Different Controlling Mechanisms of Photoinduced Charge-Order Melting in Molecular Crystals

    K. Yonemitsu, K. Nishioka

    The 5th International Conference on Photoinduced Phase Transitions and Cooperative Phenomena (PIPT5)  2014.6 

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  • Photoinduced Dynamics during Charge-Order Melting: Nonequilibrium Phonon-Frequency Modulation International conference

    K. Yonemitsu, K. Nishioka

    The 11th China-Japan Joint Symposium on Conduction and Photoconduction in Organic Solids and Related Phenomena  2013.9 

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  • Intramolecular Orbital Excitations and Frequency Modulation of Molecular Vibrations during Photoinduced Charge-Order Melting International conference

    K. Yonemitsu, K. Nishioka

    The 10th International Symposium on Crystalline Organic Metals Superconductors and Magnets (ISCOM2013)  2013.7 

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  • Out-of-equilibrium electron-phonon correlations during photoinduced melting of charge order in molecular conductors

    K. Yonemitsu, K. Nishioka

    International Conference on Electronic States and Phases Induced by Electric or Optical Impacts (IMPACT)  2012.9 

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  • Nonlinear Conduction by Melting of Charge Order in Quasi-Two-Dimensional Organic Conductors

    Y. Tanaka, K. Yonemitsu

    International Conference on Electronic States and Phases Induced by Electric or Optical Impacts (IMPACT2012)  2012.9  Orsay (France)

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  • Dynamics of Photoinduced Charge-order Melting in Intra- and Intermolecular Electron-phonon Coupled Systems

    K. Nishioka, K. Yonemitsu

    International Conference on Electronic States and Phases Induced by Electric or Optical Impacts (IMPACT2012)  2012.9  Orsay (France)

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  • Photoinduced electron-phonon interference in charge-ordered molecular conductors International conference

    K. Yonemitsu, K. Nishioka

    The 10th International Conference on Excitonic Processes in Condensed Matter, Nanostructured and Molecular Materials (EXCON2012)  2012.7 

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  • Nonequilibrium States and I-V Characteristics in One-Dimensional Band and Mott Insulators Attached to Electrodes

    Y. Tanaka, K. Yonemitsu

    The 19th International Conference on Magnetism (ICM2012) with Strongly Correlated Electron Systems (SCES)  2012.7  Busan (Korea)

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  • Roles of molecular vibrations in photoinduced insulator-to-metal and neutral-to-ionic transitions

    K. Yonemitsu

    The 9th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM2011)  2011.9 

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  • Interplay between correlated electrons and quantum phonons in photoinduced insulator-to-metal transitions

    K. Yonemitsu

    The 14th Korea-Japan Molecular Science Symposium on New Visions for Spectroscopy and Computation: Temporal and Spatial Adventures of Molecular Sciences, Busan, Korea  2011.7 

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  • Interplay between Correlated Electrons and Quantum Phonons in Organic Compounds

    K. Yonemitsu

    The 4th International Conference on Photoinduced Phase Transitions and Cooperative Phenomena (PIPT4)  2011.6 

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  • Theory of photoinduced electron-phonon-coupled dynamics in 2D charge-ordered and Mott-insulating systems

    K. Yonemitsu

    Workshop on Ultrafast Dynamics in Strongly Correlated Systems, Zurich, Switzerland  2011.4 

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  • Photoinduced phase transition dynamics: Interplay between correlated electrons and molecular vibrations during insulator-metal and neutral-ionic transitions

    K. Yonemitsu

    International School and Symposium on Multifunctional Molecule-based Materials, Argonne, Illinois, U.S.A.  2011.3 

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  • Photoinduced Insulator-to-Metal Transition Dynamics in Models for Quasi-Two-Dimensional Organic Conductors

    K. Yonemitsu, Y. Tanaka, S. Miyashita, N. Maeshima

    The 9th International Conference on Excitonic and Photonic Processes in Condensed and Nano-Materials (EXCON'10)  2010.7 

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  • Photoinduced charge-ordered insulator-to-metal transitions governed by frustration and lattice effects

    K. Yonemitsu, Y. Tanaka, S. Miyashita

    Gordon Research Conference on Ultrafast Phenomena in Cooperative Systems, Galveston, Texas, U.S.A.  2010.3 

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  • Nonequilibrium Green's Function Approach to Current-Voltage Characteristics in Two-Dimensional Charge-Ordered Systems

    Y. Tanaka, K. Yonemitsu

    5th International Symposium on Molecular Materials: Electronics, Photonics and Spintronics, Rennes, France  2009.10 

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  • Photoinduced Charge-Ordered Insulator-to-Metal Transitions Governed by Frustration and Lattice Effects

    K. Yonemitsu, Y. Tanaka

    5th International Symposium on Molecular Materials: Electronics, Photonics and Spintronics, Rennes, France  2009.10 

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  • Effects of Electron-Phonon Couplings on Charge Orders in $ \theta $- and $ \alpha $-Type BEDT-TTF Salts

    S. Miyashita, K. Yonemitsu

    International Symposium on Molecular Materials Chemistry, Solid State Physics, Theory, Nanotechnology From Molecule to Molecular Device (MOLMAT2008), Toulouse, France  2008.7 

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  • Suppression of Rectification at Interfaces between Metals and Organic Mott Insulators

    K. Yonemitsu, N. Maeshima, T. Hasegawa

    International Symposium on Molecular Materials Chemistry, Solid State Physics, Theory, Nanotechnology From Molecule to Molecular Device (MOLMAT2008), Toulouse, France  2008.7 

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  • Photoinduced Charge Order and Melting Dynamics in 1/4-Filled Organic Conductors

    K. Yonemitsu

    Gordon Research Conference on Ultrafast Phenomena in Cooperative Systems, Il Ciocco, Lucca (Barga), Italy  2008.2 

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  • Photoinduced Charge Order and Melting Dynamics in 1/4-Filled Organic Conductors

    K. Yonemitsu

    International Meeting of Japan-France Core-to-Core Project, Rennes, France  2007.12 

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  • Photoinduced Charge Order and Melting Dynamics in Quarter-Filled Organic Conductors

    K. Yonemitsu

    The 9th China-Japan Joint Symposium on Conduction and Photoconduction in Organic Solids and Related Phenomena,Beijing, China  2007.10 

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  • Photoinduced melting of charge and lattice orders viewed from theoretical transient spectra

    K. Yonemitsu

    Pre-conference PIPT 2008 Seminar, Wroclaw, Poland  2007.6 

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  • Charge ordering in $\theta$-(BEDT-TTF)_2 RbZn(SCN)_4 : Cooperative effects of electron correlations and lattice distortions

    S. Miyashita, K. Yonemitsu

    The International Conference on Science and Technology of Synthetic Metals (ICSM2006), Dublin, Ireland  2006.7 

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  • Quantum Paraelectricity near the Neutral-Ionic Critical Point

    Y. Yamashita, K. Yonemitsu

    The International Conference on Science and Technology of Synthetic Metals (ICSM2006), Dublin, Ireland  2006.7 

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  • Photoinduced dynamics of dimerized one-dimensional Mott insulators

    N. Maeshima, K. Yonemitsu

    The International Conference on Science and Technology of Synthetic Metals (ICSM2006), Dublin, Ireland  2006.7 

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  • Correlated Charge Transport through Mott-Insulator-Metal Interfaces

    K. Yonemitsu, N. Maeshima

    The International Conference on Science and Technology of Synthetic Metals (ICSM2006), Dublin, Ireland  2006.7 

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  • Mechanism of ambipolar field-effect transistors on one-dimensional organic Mott insulators

    K. Yonemitsu

    The 2005 International Chemical Congress of Pacific Basin Societies  2005.12 

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  • Photoinduced dynamics and nonequilibrium characteristics in quasi-one-dimensional electron systems: Mott insulators vs. band insulators

    K. Yonemitsu

    Second International Conference on "Photo-induced Phase Transitions; Cooperative, Non-linear and Functional Properties"  2005.5  Rennes, France

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  • Theory of photoinduced phase dynamics in organic charge-transfer complexes

    K. Yonemitsu

    6th International Conference on Excitonic Processes in Condensed Matter  2004.7 

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  • Theoretical perspectives on photoinduced phase transitions

    K. Yonemitsu

    International Seminar on "Challenges and Perspectives of Photo-induced Cooperative Phenomena," Wroclaw, Poland  2004.7 

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  • Photoinduced Dynamics of Coupled Charge-Lattice Systems in One Dimension

    K. Yonemitsu

    NEDO Europe-Japan Meeting "Intelligent Charge-Transfer Materials," Rennes, France  2002.10 

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  • Photoexcited states and photoinduced dynamics in electronic phases of MMX-chain systems

    K. Yonemitsu, N. Miyashita, M. Kuwabara

    International Conference on Science and Technology of Synthetic Metals (ICSM2002)  2002.6 

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  • Correlation and Lattice Effects on Charge Ordering and Dynamics in Quasi-One-Dimensional \pi and p-d Electron Systems

    K. Yonemitsu

    The 7th China-Japan Joint Symposium on Conduction and Photo-conduction in Organic Solids and Related Phenomena (CJOSS-7), Guangzhou, China  2001.11 

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  • Magnetic and Structural Properties of MMX Chains

    M. Kuwabara, K. Yonemitsu

    The Third International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, Oxford, UK  1999.9 

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  • Cation Effects on Ground State Phases of Pd(dmit)$_2$ Salts

    M. Mori, K. Yonemitsu, H. Kino

    The Third International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, Oxford, UK  1999.9 

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  • Geometry, Universality and Dimensional Grossovers in Weakly-Coupled One-Dimensional Conductors

    J. Kishine, K. Yonemitsu

    X Trieste Workshop on Open Problems in Strongly Conelated Electron Systems, Trieste, Italy  1998.7 

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  • Berry Phase and Symmetry of Hole Pairs in the Holstein-tJ Model

    K. Yonemitsu, J. Zhong, H.-B. Sch, u

    Workshop in the Correlated Electron Theory Program, Los Alamos, New Mexico, U. S. A.  1994.8 

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  • Dynamics of Holes in the Holstein-Hubbard Model

    K. Yonemitsu, J. Zhong, H.-B. Sch, u

    New Methods in Electronic Structure Calculations, Santa Barbara, California, U. S. A.  1994.6 

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  • Semiclassical Method for Bipolaron Tunneling

    K. Yonemitsu

    New Methods in Electronic Structure Calculations, Santa Barbara, California, U. S. A.  1994.6 

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  • Local Vibronic and Electronic Excitations of Doping-Induced States in the Copper Oxides

    K. Yonemitsu, A. R. Bisho, J. Lorenzana

    II$^{\rm nd}$ CINVESTAV Superconductivity Symposium on the Manifestations of the Electron-Phonon Interaction in High-T$_{\rm c}$ Superconductivity  1992.11 

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  • Local Excitations of Doping States in the Copper Oxides

    K. Yonemitsu, A. R. Bishop, J. Lorenzana

    Gordon Research Conference on Condensed Matter Physics : Collective States in Solids with Localized Moments, Wolfeboro, New Hampshire, U. S. A.  1992.8 

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  • RPA Approach to Collective Modes around Inhomogeneous Mean-Field States

    K. Yonemitsu, I. Batisti\'c, A. R. Bishop

    VIIth International Conference on Recent Progress in Many Body Theories, Minneapolis, Minnesota, U. S. A.  1991.8 

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▼display all

Awards

  • JPSJ Outstanding Referee

    2015.3   The Physical Society of Japan  

    YONEMITSU Kenji

  • 注目論文

    2013.9   JPSJ誌   Intra- and Interdimer Electron-Phonon Concerted Mechanism of Photoinduced Charge-Order Melting in Metal Complex Et$_2$Me$_2$Sb[Pd(dmit)$_2$]$_2$

    西岡圭太, 米満賢治

Research Projects

  • Optical functions through symmetry breaking driven by carrier-envelope phase control of light

    2019.10 - 2025.3

    Japan Science and Technology Agency  CREST  Tohoku Univ., Nagoya Univ., Osaka Univ. Chuo Univ.

    Shinichiro Iwai

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  • 強い光電場による有効相互作用の変調と創出および電子状態コヒーレント制御の理論

    2016.4 - 2022.3

    日本学術振興会学術研究助成基金助成金  科研費基盤研究(C) 

    米満 賢治

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  • 5フェムト秒極超短赤外パルス光による強相関電子系の動的局在と秩序形成の研究

    2015.4 - 2019.3

    日本学術振興会科学研究費補助金  基盤研究(A) 

    岩井 伸一郎

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  • 強相関量子物質におけるアト秒光機能の開拓

    2018.11 -  

    科学技術振興機構  光・量子飛躍フラッグシッププログラム(Q-LEAP) 

    岩井 伸一郎

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    Grant type:Competitive

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  • 分子性導体の外場誘起非線形現象における階層間結合効果の理論

    2011.4 - 2016.3

    日本学術振興会学術研究助成基金助成金  科研費基盤研究(C) 

    米満 賢治

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  • 赤外10フェムト秒パルス列による強相関電子系の電子-フォノンコヒーレント制御

    2011.4 - 2015.3

    日本学術振興会科学研究費補助金  基盤研究(A) 

    岩井 伸一郎

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    Grant type:Competitive

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  • 光技術が先導する臨界的非平衡物質科学

    2009.11 - 2015.3

    科学技術振興機構  戦略的創造研究推進事業 

    腰原 伸也

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    Grant type:Competitive

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  • 量子熱電効果の非平衡物理と熱駆動ナノデバイスの開拓

    2008.4 - 2012.3

    日本学術振興会科学研究費補助金  基盤研究(B) 

    中村 浩章

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    Grant type:Competitive

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  • 次世代ナノ統合シミュレーションソフトウェアの研究開発

    2006.4 - 2012.3

    文部科学省  科学技術試験研究委託業務 

    平田 文男

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    Grant type:Competitive

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  • 分子性低次元導体の光誘起相転移動力学の理論

    2007.4 - 2011.3

    日本学術振興会科学研究費補助金  科研費基盤研究(C) 

    米満 賢治

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  • 強相関電子系ナノワイヤー金属錯体の科学

    2003.4 - 2008.3

    日本学術振興会科学研究費補助金  学術創成研究費 

    山下 正廣

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    Grant type:Competitive

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  • 極限環境下の分子性導体における集団的な電荷ダイナミクスの理論

    2003.4 - 2008.3

    文部科学省科学研究費補助金  特定領域研究(計画研究) 

    米満 賢治

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  • 分子性物質の光誘起相転移と非平衡秩序形成

    2003.4 - 2007.3

    日本学術振興会科学研究費補助金  基盤研究(C) 

    米満 賢治

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  • 超高速コンピュータ網形成プロジェクト(NAREGI)

    2003.4 - 2006.3

    文部科学省  科学技術振興費産学連携等研究費 

    平田 文男

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    Grant type:Competitive

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  • 電荷移動錯体ナノ界面創製

    2000.4 - 2003.3

    NEDO国際共同研究助成 

    三谷 忠興

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    Grant type:Competitive

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  • 低次元分子性導体の電荷秩序と絶縁機構、光誘起非線型ダイナミクス

    2000.4 - 2003.3

    日本学術振興会科学研究費補助金  基盤研究(C) 

    米満 賢治

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  • 集積型金属錯体の電子構造理論

    1998.4 - 2002.3

    文部科学省科学研究費補助金  特定領域研究(計画研究) 

    山口 兆

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  • 二バンド系における強相関電子相と次元クロスオーバー

    1998.4 - 2000.3

    日本学術振興会科学研究費補助金  奨励研究(A) 

    米満 賢治

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    Authorship:Principal investigator  Grant type:Competitive

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  • 微小磁性体中の束縛された電子の運動と伝導性、トンネル現象の研究

    1997.4 - 1998.3

    文部省科学研究費補助金  重点領域研究(公募研究) 

    米満 賢治

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    Authorship:Principal investigator  Grant type:Competitive

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  • 分子性物質の電子理論

    1996.4 - 1997.3

    文部省科学研究費補助金  重点領域研究(計画研究) 

    永長 直人

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    Grant type:Competitive

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  • 半充填近傍のスピンギャップと束縛対生成に対するフォノンの効果

    1996.4 - 1997.3

    文部省科学研究費補助金  重点領域研究(公募研究) 

    米満 賢治

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    Authorship:Principal investigator  Grant type:Competitive

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  • 低次元分子性導体の磁場誘起相と量子効果における幾何学的位相と電子相関

    1995.4 - 1996.3

    文部省科学研究費補助金  重点領域研究(公募研究) 

    米満 賢治

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    Authorship:Principal investigator  Grant type:Competitive

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  • モット転移近傍の準粒子の運動とホール伝導、非BCS超伝導及び幾何学的位相

    1995.4 - 1996.3

    文部省科学研究費補助金  重点領域研究(公募研究) 

    米満 賢治

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    Authorship:Principal investigator  Grant type:Competitive

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  • Condensed Matter Theory of Low-Dimensional Molecular Materials

    Grant-in-Aid for Scientific Research 

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    Grant type:Competitive

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Teaching Experience

  • 固体物性理工学

  • 物理学第一特別講義7:低次元物質系の相転移ダイナミクス

  • 低次元分子性導体の物性理論

  • 特別講義III:低次元有機導体の物性理論

  • 低次元分子性固体の物性理論

  • 物性科学概論

  • 分子集団動力学

  • 数学演習

  • 数学B

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Committee Memberships

  • 2015.8 - 2017.7

    日本学術振興会   特別研究員等審査会専門委員及び国際事業委員会書面審査員  

  • 2006.3 - 2016.3

    Journal of the Physical Society of Japan   編集委員  

  • 2007.9 - 2013.8

    日本物理学会   第63期~第64期代議員  

  • 2011.5 - 2012.3

    日本物理学会   領域5(光物性分野)領域運営委員  

  • 2008.8 - 2011.3

    日本学術振興会   研究開発専門委員会「ナノ物質量子相の科学」委員  

  • 2008.8 - 2010.7

    日本学術振興会   特別研究員等審査会専門委員及び国際事業委員会書面審査員  

  • 2003.5 - 2004.4

    日本物理学会   領域7(分子性固体・有機導体分野)世話人  

  • 2000.9 - 2001.8

    日本物理学会   第56期代議員  

  • 1998.9 - 2000.8

    日本物理学会   名古屋支部委員  

  • 1998.9 - 1999.8

    日本物理学会   日本物理学会誌, 編集委員  

  • 1996.9 - 1997.8

    日本物理学会   名古屋支部委員  

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