Researchers Database


    Graduate School of Science and Engineering Engineering for Production and Environment Associate Professor
Last Updated :2020/10/13

Researcher Information

Research funding number

  • 20511017

J-Global ID

Research Interests

  • 分子性伝導体   分子固体   材料力学   高圧物性   振動分光学   物性科学   分子分光学   固体科学   物理化学   

Academic & Professional Experience

  • 2018/04 - Today  Ehime University准教授(兼任)
  • 2013/04 - Today  Ehime UniversityGraduate School of Science and Engineering准教授
  • 2008/04 - Today  理化学研究所客員研究員
  • 2008/04 - 2013/03  Osaka UniversityGraduate School of Science助教
  • 2005/04 - 2008/03  日本学術振興会 特別研究員PD
  • 2002/04 - 2005/03  岡崎国立共同研究機構 分子科学研究所(2004年より自然科学研究機構 分子科学研究所)研究機関研究員 (2004年より研究員)
  • 1999/04 - 2002/03  日本学術振興会 特別研究員DC1


  • 1999/04 - 2002/03  The University of Tokyo  Graduate School of Science
  • 1997/04 - 1999/03  The University of Tokyo  Graduate School of Science
  • 1993/04 - 1997/03  The University of Tokyo  Faculty of Science  Department of Chemistry

Association Memberships


Published Papers

  • Takashi Yamamoto, Takashi Fujimoto, Toshio Naito, Yasuhiro Nakazawa, Masafumi Tamura, Kyuya Yakushi, Yuka Ikemoto, Taro Moriwaki, Reizo Kato
    SCIENTIFIC REPORTS 7 2045-2322 2017/10 Scientific journal 
    Spin liquid (SL) systems have been the subject of much attention recently, as they have been theoretically predicted to not freeze, even at 0 K. Despite extensive searches being made for such a system, only a few candidates have been found. All of these candidates share geometrical frustrations that are based on triangular lattices. We applied vibrational spectroscopy to one of the candidates of a molecule-based SL system, and we compared its results against three antiferromagnetic compounds and four charge-ordered compounds. All of their structural motifs belong to triangular lattices. The C=C stretching modes in the SL state indicated that there were charge and lattice fluctuations. These fluctuations were suppressed but non-negligible in the AF compounds. This finding is potentially significant, as it indicates that a hidden lattice and charge fluctuation are the driving force of a geometrical frustration, which eventually leads to a SL state.
  • Shuhei Fukuoka, Satoshi Yamashita, Yasuhiro Nakazawa, Takashi Yamamoto, Hideki Fujiwara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 (1) 0031-9015 2017/01 Scientific journal 
    Angle-resolved heat capacity measurements of a pi-d interacting system of kappa-(BETS)(2)FeBr4 [BETS = bis(ethylene-dithio) tetraselenafulvalene] with in-plane magnetic fields are performed. We observed a thermal anomaly in association with the superconducting transition of the pi electrons in the pi-d compound for the first time. By pursuing a systematic change in the thermal anomaly, we found that the thermodynamic feature of the superconducting state shows large anisotropy against in-plane magnetic fields. When the field is applied parallel to the c-axis, the thermal anomaly remains up to 2.6 T with a distinct peak structure. On the other hand, it is suppressed in synchrony with the decrease of the antiferromagnetic transition temperature, when the field is applied parallel to the a-axis. Our thermodynamic results indicate that the effect of the pi-d interaction appears even when the pi electrons are itinerant and that the anisotropic field-direction dependence of the superconducting transition originates from the correlation between superconductivity and magnetism.
  • Takashi Yamamoto, Masafumi Tamura, Kyuya Yakushi, Reizo Kato
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 85 (10) 0031-9015 2016/10 Scientific journal 
    We have carried out the complete analyses of the C=C stretching modes in the vibrational spectra in the triangular lattice of beta'-Cs[Pd(dmit)(2)](2) in order to solve the puzzling phenomenon that the ground state is neither spin frustration nor anti-ferromagnetic state but octamerization. We found that both charge-rich and charge-poor dimers are non-centrosymmetric dimers with the inhomogeneous charges. Because the energy levels of HOMO and LUMO are interchanged due to the tight dimerization, the cooperative interaction between the inter-site Coulomb repulsions and the valence-bond formation operates within and between dimers, those which contribute to the inter-dimer and intra-dimer charge separations, respectively. Octamer is the minimal unit under both cooperative interactions. In the high-temperature phase of beta'-Cs[Pd(dmit)(2)](2), the competition between octamerization and tetramerization is observed because of the suppression of the intra-dimer cooperative interaction. The competition between two different states indicates the degree of freedom characteristic of the molecular orbital due to the tight dimerization. The cooperative interactions of the various X[Pd(dmit)(2)](2) salts are quantitatively evaluated from the C=C stretching modes.
  • Shuhei Fukuoka, Satoshi Yamashita, Yasuhiro Nakazawa, Takashi Yamamoto, Hideki Fujiwara, Takashi Shirahata, Kazuko Takahashi
    PHYSICAL REVIEW B 93 (24) 2469-9950 2016/06 [Peer-reviewed]
     Scientific journal 
    The results are presented for systematic heat capacity measurements of pi-d interacting systems of kappa-(BETS)(2)FeBr4 and kappa-(BETS)(2)FeCl4 [BETS = bis(ethylenedithio)tetraselenafulvalene] performed under in-plane magnetic fields. We observed sharp thermal anomalies at 2.47 K for kappa-(BETS)(2)FeBr4 and at 0.47 K for kappa-(BETS)(2)FeCl4 at 0 T that are associated with antiferromagnetic transitions of the 3d electrons in the anion layers. From analyses of the magnetic heat capacity data, we indicate that the two compounds show unconventional thermodynamic behaviors inherent in the pi-d interacting layered system. In the case of kappa-(BETS)(2)FeBr4, a small hump structure was observed in the magnetic heat capacity below the transition temperature when a magnetic field was applied parallel to the a axis. In the case of kappa-(BETS)(2)FeCl4, a similar hump structure was observed at 0 T that remained in the data with magnetic fields applied parallel to the a axis. We demonstrate that the temperature dependencies of the magnetic heat capacities scale well by normalizing the temperatures with dominant one-dimensional direct interactions (J(dd)/k(B)) of each compound. The field dependencies of the transition temperatures and the hump structures are elucidated in one simple magnetic field vs temperature (H-T) phase diagram. These results indicate that the thermodynamic features of both kappa-type BETS salts are essentially equivalent, and the observed hump structures are derived from the one-dimensional J(dd) interaction characters, which are still influential for magnetic features even in the long-range magnetic ordered states.
  • Tadahiko Ishikawa, Stuart A. Hayes, Sercan Keskin, Gaston Corthey, Masaki Hada, Kostyantyn Pichugin, Alexander Marx, Julian Hirscht, Kenta Shionuma, Ken Onda, Yoichi Okimoto, Shin-ya Koshihara, Takashi Yamamoto, Hengbo Cui, Mitsushiro Nomura, Yugo Oshima, Majed Abdel-Jawad, Reizo Kato, R. J. Dwayne Miller
    SCIENCE 350 (6267) 1501 - 1505 0036-8075 2015/12 Scientific journal 
    Correlated electron systems can undergo ultrafast photoinduced phase transitions involving concerted transformations of electronic and lattice structure. Understanding these phenomena requires identifying the key structural modes that couple to the electronic states. We report the ultrafast photoresponse of the molecular crystal Me4P[Pt(dmit)(2)](2), which exhibits a photoinduced charge transfer similar to transitions between thermally accessible states, and demonstrate how femtosecond electron diffraction can be applied to directly observe the associated molecular motions. Even for such a complex system, the key large-amplitude modes can be identified by eye and involve a dimer expansion and a librational mode. The dynamics are consistent with the time-resolved optical study, revealing how the electronic, molecular, and lattice structures together facilitate ultrafast switching of the state.
  • Kyuya Yakushi, Kaoru Yamamoto, Takashi Yamamoto, Yohei Saito, Atsushi Kawamoto
    Journal of the Physical Society of Japan 84 0031-9015 2015/08 
    ©2015 The Physical Society of Japan. We present experimental evidence for the charge fluctuation in the spin-liquid candidate κ-(BEDT-TTF) < inf > 2 < /inf > Cu < inf > 2 < /inf > (CN) < inf > 3 < /inf > . The temperature and pressure dependence of the Raman spectrum in the region of 1300-1600 cm < sup > -1 < /sup > were measured. The charge-sensitive ν < inf > 2 < /inf > mode at 1500 cm < sup > -1 < /sup > exhibited a linewidth broadening below 60 K when the sample was slowly cooled. This broadening is induced by a structural change (increase in interdimer transfer integrals). The hydrostatic pressure significantly suppressed the broadening in the metallic phase. This result indicates that the linewidth broadening originates from the valence (charge) fluctuation within the BEDT-TTF dimer, because the screening effect suppresses the interdimer Coulomb interaction that causes the charge disproportionation. The line shape was analyzed using the fast fluctuating model and slow or static inhomogeneous model.
  • Activation energy for photoconduction in molecular crystals
    N. Nagayama, T. Yamamoto, T. Naito
    CheM 2 74 - 80 2015 [Peer-reviewed]
     Scientific journal
  • Takashi Yamamoto, Yasuhiro Nakazawa, Masafumi Tamura, Akiko Nakao, Atsuko Fukaya, Reizo Kato, Kyuya Yakushi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 (5) 0031-9015 2014/05 Scientific journal 
    We have investigated the property of the non-magnetic insulating state of a pressure-induced molecular superconductor with a quasi-triangular lattice consisting of tight dimer units applying vibrational and reflectance spectroscopy to monoclinic-phase of C2H5(CH3)(3)P[Pd(dimt)(2)](2) (dmit = 1,3-dithiole-2-thione-4,5-dithiolate). From the analyses of the spectra, it is founded that two asymmetric dimers form a weakly bounded tetramer and the 2D layer is a slightly anisotropic. Theses results indicate that the cooperation between nearest Coulomb repulsions and valence bond order, which is operative for the anisotropic system of triclinic-phase of C2H5(CH3)(3)P[Pd(dimt)(2)](2), inhibits spin frustration in the monoclinic-phase. Our result also suggests that a half-filled picture does not always hold for the molecular superconductors consisting of tight dimer units.
  • Guoyang Guan, Shuhei Fukuoka, Satoshi Yamashita, Takashi Yamamoto, Hiromi Taniguchi, Yasuhiro Nakazawa
    JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 113 (3) 1197 - 1201 1388-6150 2013/09 Scientific journal 
    Thermodynamic investigation using the relaxation calorimetry technique and the microchip calorimetry technique is performed to clarify low-temperature behaviors of a radical cation salt consisting of a donor molecule of bispropylenedithiotetrathiafulvalene (BPDT-TTF) and a linear anion of . This compound has a layered structure similar to numerous BEDT-TTF compounds. The donor molecules form a dimerized arrangement in the layer. Temperature dependence of heat capacity obtained by the relaxation technique shows a broad hump structure around 20-25 K corresponding to the temperature where the magnetic susceptibility shows a drastic decrease due to the formation of the singlet spin state. The microchip calorimetry technique detected a step-like anomaly around 23 K in the temperature dependence of C (p) T (-1) of which entropy is evaluated as only few % of Rln2 corresponding to the full entropy of localized pi-electrons located on each dimer unit. The negligibly small T-linear term in the low-temperature heat capacity and absence of magnetic fields dependence below 3.2 K predict opening of rigid gap structure in the spin excitations, which is consistent with a spin-singlet formation due to the formation of spin-Peierls type ordering or charge ordering state.
  • Naoto Fukazawa, Takahiro Tanaka, Tadahiko Ishikawa, Yoichi Okimoto, Shin-ya Koshihara, Takashi Yamamoto, Masafumi Tamura, Reizo Kato, Ken Onda
    JOURNAL OF PHYSICAL CHEMISTRY C 117 (25) 13187 - 13196 1932-7447 2013/06 [Peer-reviewed]
     Scientific journal 
    To clarify the mechanism of the later process of photoinduced phase transition (PIPT) in organic charge-transfer complexes, we examined by time-resolved infrared vibrational spectroscopy two dimeric anion radical salts, Et2Me2Sb[Pd(dmit)(2)](2) (Et2Me2Sb salt) and Cs[Pd(dmit)(2)](2) (Cs salt) (Et, Me, and dmit are C2H5, CH3, and 1,3-dithiol-2-thione-4,5-dithiolate, respectively), having similar characteristics except for the order of their phase transitions at thermal equilibrium. The phase transition is first order for the Et2Me2Sb salt and second order for the Cs salt at thermal equilibrium. Although both salts exhibit a high-temperature phase at later delay times (>100 ps) after the photoexcitation of the low-temperature phase, the time required for the emergence of the high-temperature phase was significantly different: 70 ps for the Et2Me2Sb salt and <0.1 ps for the Cs salt. The slow emergence of the high-temperature phase in the PIPT of the Et2Me2Sb salt presumably has an origin similar to that recognized for the first-order thermal phase transition, that is, steric effects of the Et2Me2Sb cation when the phase transitions occur.
  • Takashi Yamamoto
    CRYSTALS 2 (3) 893 - 934 2073-4352 2012/09 [Peer-reviewed]
    The relationship between the conducting behavior and the degree of charge fluctuation in the beta ''-type BEDT-TTF salts is reviewed from the standpoints of vibrational spectroscopy and crystal structure. A group of beta ''-type ET salts demonstrates the best model compounds for achieving the above relationship because the two-dimensional structure is simple and great diversity in conducting behavior is realized under ambient pressure. After describing the requirement for the model compound, the methodology for analyzing the results of the vibrational spectra is presented. Vibrational spectroscopy provides the time-averaged molecular charge, the charge distribution in the twodimensional layer, and the inter-molecular interactions, etc. The experimental results applied to 2/3-filled and 3/4-filled beta ''-type ET salts are reported. These experimental results suggest that the conducting property, the difference in the time-averaged molecular charges between the ionic and neutral-like sites, the alternation in the inter-molecular distances and the energy levels in the charge distributions are relevant to one another. The difference in the time-averaged molecular charges, Delta rho, is a useful criterion for indicating conducting behavior. All superconductors presented in this review are characterized as small but finite Delta rho.
  • Takashi Yamamoto, Yasuhiro Nakazawa, Masafumi Tamura, Kyuya Yakushi, Reizo Kato
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 249 (5) 971 - 974 0370-1972 2012/05 Scientific journal 
    A group of [Pd(dmit)2]2 salts, whose two-dimensional structures take (pesudo-) triangular lattice, has a diversity in the ground states. In order to investigate the ground states, we have developed the methodology for analysing subtle changes in the inter-molecular interactions and MO level using the vibrational and electronic spectroscopy. This methodology is applied to several [Pd(dmit)2]2 salts. We have found some relationships between the ground states and the inter-dimer and intra-dimer interactions under HOMOLUMO inversion.
  • Yuki Muraoka, Satoshi Yamashita, Takashi Yamamoto, Yasuhiro Nakazawa
    THERMOCHIMICA ACTA 532 88 - 91 0040-6031 2012/03 [Peer-reviewed]
     Scientific journal 
    We carried out thermodynamic measurements of organic charge transfer complex of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene by TCG3880 chip device in order to examine capability of the chip calorimeter at low temperature region and under magnetic fields. TCG3880 chip is mounted on a He-3 cryostat available in combination with a superconductive magnet up to 7T. Thermal anomalies related to the glass-like freezing of ethylene groups of BEDT-ITF molecules and the superconductive transition were observed. A frequency dependence of the thermal anomaly of the glass formation and a magnetic fields dependence of the thermal anomaly of the superconductive transition are reported. The results presented in this work demonstrate that the TCG3880 is quite useful for thermodynamic investigations of the organic charge transfer complex with much reduced sample quantity as compared with those of relaxation and adiabatic calorimetry. (C) 2011 Elsevier B.V. All rights reserved.
  • High-Pressure AC Calorimetry System Using Pt Chip Thermometer
    Mayu Danda, Yuki Muraoka, Takashi Yamamoto, Yasuhiro Nakazawa
    Calorimetry and Thermal Analysis (Netsu Sokutei) W39 29 - 32 2012 [Peer-reviewed]
     Scientific journal
  • Shuhei Fukuoka, Satoshi Yamashita, Takashi Yamamoto, Yasuhiro Nakazawa, Akiko Kobayashi, Hayao Kobayashi
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 5 9 (5) 1174 - 1176 1862-6351 2012 International conference proceedings 
    Low temperature thermodynamic properties of kappa-(BETS)(2)FeBr4 are studied by using a tiny single crystal sample with 1 mu g adhered on a micro-chip calorimeter TCG3880. A large thermal anomaly associated with the antiferromagnetic transition of localized d electrons of Fe3+ was observed around 2.2 K. With the increase of magnetic fields applied parallel to the ac plane, the transition temperature shifts to lower temperature side accompanied by an anisotropic character. We found that the reduction of the transition temperature is largest, when magnetic field was applied parallel to a-axis. This observation is consistent with the previous result obtained by transport measurements which claimed that the spin easy axis is a-axis. The results demonstrate that the microchip calorimeter is effective for conducting thermodynamic measurements of molecular compounds. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Takashi Yamamoto, Yasuhiro Nakazawa, Masafumi Tamura, Akiko Nakao, Yuka Ikemoto, Taro Moriwaki, Atsuko Fukaya, Reizo Kato, Kyuya Yakushi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (12) 0031-9015 2011/12 [Peer-reviewed]
     Scientific journal 
    Molecular conductors consisting of "tight dimers" with short intermolecular distances have been studied from the viewpoint of the 1/2-filled picture. Triclinic-EtMe3P[Pd(dmit)(2)](2) [dmit = 1,3-dithiole-2-thione-4,5-dithiolate] exhibits the intradimer charge ordered state CO(intra) below 50 K and charge fluctuation above 50 K. In both CO(intra) and fluctuated states, the intradimer Coulomb repulsion V-d, the interdimer Coulomb repulsions V-i, and the valence bond ordering cooperate with one another, which is characteristic of highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) inversion system. This observation is evidence of the localization due to the 1/4-filled picture. This result prompts us to construct a unified physical model applicable to a wide range of molecular conductors composed of not only tight dimers but also nontight dimers.
  • Kazuya Kubo, Takuya Shiga, Takashi Yamamoto, Akiko Tajima, Taro Moriwaki, Yuka Ikemoto, Masahiro Yamashita, Elisa Sessini, Maria Laura Mercuri, Paola Deplano, Yasuhiro Nakazawa, Reizo Kato
    INORGANIC CHEMISTRY 50 (19) 9337 - 9344 0020-1669 2011/10 Scientific journal 
    The electrochemical oxidation of an acetone solution containing [Mn-III (5-MeOsaltmen)(H2O)](2)(PF6)(2) (5-MeOsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylen e)bis (5-methoxysalicylideneiminate)) and (NBu4)[Ni(dmit)(2)] (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate) afforded a hybrid material, [Mn(5-MeOsaltmen)(acetone)](2)[Ni(dmit)(2)](6) (1), in which [Mn-2](2+) single-molecule magnets (SMMs) with an S-T = 4 ground state and [Ni(dmit)(2)](n-) molecules in a charge-ordered state (n = 0 or 1) are assembled in a layer-by-layer structure. Compound 1 crystallizes in the triclinic space group P (1) over bar with an inversion center at the midpoint of the Mn center dot center dot center dot Mn dimer. The [Mn-2](2+) unit has a typical nonplanar Mn(III) dimeric core and is structurally consistent with previously reported [Mn2] SMMs. The six [Ni(dmit)(2)](n-) (n = 0 or 1) units have a square-planar coordination geometry, and the charge ordering among them was assigned on the basis of v(C=C) in IR reflectance spectra (1386, 1356, 1327, and 1296 cm(-1)). The [Mn-2](2+) SMM and [Ni(dmit)(2)](n-) units aggregate independently to form hybrid frames. Electronic conductivity measurements revealed that 1 behaved as a semiconductor (rho(rt) = 2.1 x 10(-1), E-a = 97 meV) at ambient pressure and as an insulator at 1.7 GPa (rho(1.7GPa) = 4.5, E-a = 76 meV). Magnetic measurements indicated that the [Mn-2](2+) units in 1 behaved as S-T = 4 SMMs at low temperatures.
  • Takashi Yamamoto, Yakuhiro Nakazawa, Masafumi Tamura, Takeo Fukunaga, Reizo Kato, Kyuya Yakushi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (7) 0031-9015 2011/07 Scientific journal 
    We have developed a methodology for analyzing the lattice, charge, and orbital in two-dimensional molecular conductors comprising dimers of [Pd(dimt)(2)] ([Pd(dimt)(2)](2)) using C=C stretching vibrational modes. After confirming vibrational modes for non-dimerized and loosely dimerized materials, we provide assignments for the four C=C stretching modes-two IR-active modes and two Raman-active modes-for the tight dimer. Of the four modes, the Raman-active and the lowest frequency mode is attributed to redistribution of the molecular orbital due to tight dimerization. By analyzing the vibrational spectra in the charge-ordered (CO) state of Et2Me2Sb[Pd(dmit)(2)](2), we have found that the four modes are reflect in the intra-dimer interaction, the inter-dimer interaction, molecular charges and orbital levels. The results suggest that the vibrational spectroscopy is a powerful method to investigate electronic correlations, electron-phonon interactions, etc. in [Pd(dimt)(2)] salts.
  • Satoshi Yamashita, Takashi Yamamoto, Yasuhiro Nakazawa, Masafumi Tamura, Reizo Kato
    NATURE COMMUNICATIONS 2 2041-1723 2011/04 [Peer-reviewed]
     Scientific journal 
    In frustrated magnetic systems, long-range ordering is forbidden and degeneracy of energy states persists, even at extremely low temperatures. Under certain conditions, these systems form an exotic quantum spin-liquid ground state, in which strongly correlated spins fluctuate in the spin lattices. Here we investigate the thermodynamic properties of an anion radical spin liquid of EtMe3Sb[Pd(dmit)(2)](2), where dmit represents 1,3-dithiole-2-thione-4,5-dithiolate. This compound is an organic dimer-based Mott insulator with a two-dimensional triangular lattice structure. We present distinct evidence for the formation of a gapless spin liquid by examining the T-linear heat capacity coefficient, gamma, in the low-temperature heat capacity. Using comparative analyses with kappa-(BEDT-TTF)(2)Cu-2(CN)(3), a generalized picture of the new spin liquid in dimer-based organic systems is discussed. We also report anomalous enhancement of gamma, produced by a kind of criticality inherent to the Pd(dmit)(2) phase diagram.
  • Y. Muraoka, S. Yamashita, T. Yamamoto, Y. Nakazawa
    INTERNATIONAL CONFERENCE ON FRUSTRATION IN CONDENSED MATTER (ICFCM) 320 1742-6588 2011 International conference proceedings 
    Thermodynamic measurements of an organic spin liquid compound of kappa-(BEDT-TTF)(2)Cu(2)(CN)(3) where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene were performed by the ac calorimetry technique using a microchip device of TCG3880. This technique is effective to measure relative temperature and magnetic-field dependences of heat capacity for tiny single crystal samples less than 1 mu g. Broad hump structures in C(p) vs T which are known as so-called 6 K anomaly were observed in kappa-(BEDT-TTF)(2)Cu(2)(CN)(3) and its deuterated compound. The hump temperatures are evaluated as 5.7 K in both compounds. This result demonstrates that the TCG3880 is useful for performing thermodynamic investigations of such kind of organic charge transfer complexes with much reduced sample quantity than the conventional techniques and that the existence of hump structure is intrinsic for kappa-(BEDT-TTF)(2)Cu(2)(CN)(3). The in-plane angular dependence of the magnetic field of 7 T applied parallel to the two dimensional layer is also studied and absence of in-plane anisotropy of the hump structure is discussed in both pristine and deuterated compounds.
  • S. Yamashita, T. Yamamoto, Y. Nakazawa
    PHYSICA B-CONDENSED MATTER 405 (11) S240 - S243 0921-4526 2010/06 Scientific journal 
    Heat capacity measurements of organic triangular lattice compound kappa-(BEDT-TTF)(2)Cu-2(CN)(3) were performed to discuss the low energy excitations from the spin-liquid ground states Existence of the T-linear electronic coefficient with finite electronic heat capacity coefficient gamma was confirmed in three different samples from different batches although small sample dependence was observed in the absolute values of the heat capacities Concerning the sample in which hydrogen atoms in ethylene group in BEDT-TTF molecule have been substituted by deuterons we have observed almost similar thermodynamic behavior as the hydrogenated sample The absence of drastic change of electronic properties of this compound is consistent with the electronic phase diagram given by Kurosaki et al [11] (Phys Rev Lett 95 (2005) 17001) The obtained data are well consistent with the previous heat capacity experiments The existence of the gamma term demonstrates that the excitations from the quantum spin-liquid states show a gapless behavior at least down to 0 7 K (C) 2010 Elsevier B V All rights reserved
  • Shuhei Fukuoka, Satoshi Yamashita, Takashi Yamamoto, Yasuhiro Nakazawa, Hiroyuki Higashikawa, Katsuya Inoue
    Physica B: Condensed Matter 405 0921-4526 2010/06 
    Thermodynamic nature of the magnetic transitions of a cyano-bridged W V -Cu II compound of [W(CN) 8 ] 4 [Cu(pn) H 2 O] 4 [Cu(pn)] 2 ·2.5H 2 O is studied by low-temperature heat capacity measurements. Distinct thermal anomalies were observed in the temperature dependence of the heat capacity at 7.8 K for chiral compound (S-enantiomer) and 7.2 K for racemic compound. They are associated with the antiferromagnetic transitions reported by the previous magnetization measurements. In the case of S-enantiomer, a shoulder structure of C p /T has been observed just below the main peak of the antiferromagnetic transition temperature at 0T. The shoulder grows to a sharp anomaly with a first order character by applying magnetic field of about 1 T in the b-axis direction. On the other hand, just a broadening of the peak was observed for racemic compound, which means that the complicated behavior under magnetic field is derived from the crystallographic chirality. We also studied the behavior of S-enantiomer with magnetic fields applied parallel to the c-axis and found that the first order transition is not induced. Appearance of the complicated peak structure including the first order character specific in the b-direction is ascribed to peculiar magnetic ordering derived from crystallographic chirality related to the Dzyaloshinskii-Moriya (DM) interaction. © 2010 Elsevier B.V. All rights reserved.
  • T. Yamamoto, Y. Nakazawa, R. Kato, K. Yakushi, H. Akutsu, A. S. Akustu, H. Yamamoto, A. Kawamoto, S. S. Turner, P. Day
    PHYSICA B-CONDENSED MATTER 405 (11) S237 - S239 0921-4526 2010/06 Scientific journal 
    In recent years concern has been raised about the charge fluctuation of the superconducting transition in the loosely dimerized molecular conductors Not only the observation of the charge fluctuation is of considerably important but also the understanding of the mechanism of the fluctuation We have observed degree of charge fluctuation of several beta ''-type ET salts The beta ''-type ET salt is one of the best model compounds because the direction of the largest inter-site Coulomb interaction is perpendicular to that of the largest transfer integral This structural property allows us to examine the role of inter-site Coulomb interaction from the viewpoint of the inter-molecular distance The difference in the molecular charges between the charge rich site and the charge poor sites Delta rho is correlated with the conducting behavior the superconducting materials have the small but finite Delta rho whereas Delta rho of the insulating (metallic) materials is large (almost zero) After the analysis of the configuration in the intermolecular distances, we have found that the degree of fluctuation Delta rho is attributed to the number of the most stable charge distribution(s) N(s) and the number of the energy levels of the allowed charge distribution N(A) The superconducting materials belong to the condition of N(s) >= 2 and N(A) >= 2 Indeed this condition contributes to the fluctuation of the molecular charges (C) 2009 Elsevier B V All rights reserved
  • Kazuya Kubo, Akiko Nakao, Yasuyuki Ishii, Takashi Yamamoto, Masafumi Tamura, Reizo Kato, Kyuya Yakushi, Gen-etsu Matsubayashi
    INORGANIC CHEMISTRY 47 (12) 5495 - 5502 0020-1669 2008/06 Scientific journal 
    The electronic properties of cation radical salts derived from organometallic mixed-ligand complexes [(ppy)Au(S-S)] (ppy(-) = C-dehydro-2-phenylpyridine(-); S-S2- = dithiolene ligand) with Au(III)-C sigma-bond were investigated. A 2:1 salt complex [(ppy)Au(C8H4S8)](2)[PF6] (C8H4S82- = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) exhibited semiconductive behavior under ambient pressure (rho(rt) = 2.6 Omega cm, E-a = 0.03 eV). Magnetic measurements show that it is a Mott insulator close to the metal-insulator boundary. Raman and infrared spectra have revealed that the complex has a quasi-one-dimensional dimeric structure consisting of uniformly charged donor molecules. The complex exhibits metallic behavior at pressures above 0.8 GPa. In contrast, a similar compound [(ppy)Au(C8H4S6O2)](2)[BF4] (C8S6O22- = 2-{(4,5-ethylenedioxy)-1,3-dithiole-2-ylidenel-1,3-dithiole-4,5-dithiolate(2-)) is a band insulator.
  • Masayuki Tanaka, Kaoru Yamamoto, Mikio Uruichi, Takashi Yamamoto, Kyuya Yakushi, Shinya Kimura, Hatsumi Mori
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (2) 0031-9015 2008/02 [Peer-reviewed]
     Scientific journal 
    We present spectroscopic evidence for charge ordering in beta-(meso-DMBEDT-TTF)(2)PF6 below similar to 70 K. Its infrared and Raman spectra change abruptly at similar to 70 K. The amplitude of the charge order was estimated to be 0.5 from the splitting of the infrared-active C=C stretching mode. The coexistence of both high-temperature and low-temperature signals was observed in a narrow temperature range (similar to 4 K) near the phase transition temperature. The pressure and temperature phase diagram was obtained in the vicinity of the superconducting phase. The checkerboard-type charge-order phase is not directly adjacent to the superconducting phase, but the superconducting phase is adjacent to the insulating phase where the short-range ordered domain of charge order is growing. The coexistent region expands significantly when hydrostatic pressure is applied. In the coexistent region, the crystal is inhomogeneous not just on a macroscopic scale, but also on a mesoscopic scale.
  • Hiroshi M. Yamamoto, Yamamoto, Takashi, Yamamoto, Hiroshi M., Kato, Reizo, Uruichi, Mikio, Yakushi, Kyuya, Akutsu, Hiroki, Sato-Akutsu, Akane, Kawamoto, Atsushi, Turner, Scott S., Day, Peter
    Physical Review B 77 (20) 1098-0121 2008 [Peer-reviewed]
     Scientific journal
  • Takashi Yamamoto, Reizo Kato, Hiroshi M. Yamamoto, Atsuko Fukaya, Kenji Yamasawa, Ichiro Takahashi
    REVIEW OF SCIENTIFIC INSTRUMENTS 78 (8) 0034-6748 2007/08 Scientific journal 
    We have developed a technique for the anisotropic extension of fragile molecular crystals. The pressure medium and the instrument, which extends the pressure medium, are both made from epoxy resin. Since the thermal contraction of our instrument is identical to that of the pressure medium, the strain applied to the pressure medium has no temperature dependence down to 2 K. Therefore, the degree of extension applied to the single crystal at low temperatures is uniquely determined from the degree of extension in the pressure medium and thermal contractions of the epoxy resin and the single crystal at ambient pressure. Using this novel instrument, we have measured the temperature dependence of the electrical resistance of metallic, superconducting, and insulating materials. The experimental results are discussed from the viewpoint of the extension (compression) of the lattice constants along the parallel (perpendicular) direction.
  • Takashi Yamamoto, Junya Eda, Akiko Nakao, Reizo Kato, Kyuya Yakushi
    PHYSICAL REVIEW B 75 (20) 1098-0121 2007/05 [Peer-reviewed]
     Scientific journal 
    We have carried out x-ray structural analysis and have studied the temperature dependence of vibrational spectra and electrical resistivity under uniaxial strain for (ET)(5)Te2I6 and (BETS)(5)Te2I6 [ET=bis(ethylenedithio)tetrathiafulvalene and BETS=bis(ethylenedithio)tetraselenafulvalene]. In the low-temperature insulating phase for each salt, a charge-sensitive mode nu(2) exhibits peak splitting, and a vibronic nu(3) mode shows factor group splitting. This observation confirms the charge ordered state. The distribution of site charges is determined from the factor group analysis of the vibronic nu(3) mode, which is in agreement with that determined from x-ray structural analysis of the ET salt. In the high-temperature conducting phase, the vibronic nu(3) mode is smeared out whereas the frequencies of the two charge-sensitive modes are almost unchanged over the whole temperature range. We have proposed a model wherein the highly conducting state is ascribed to the frustration between the site-charge distributions in the insulating state and the other distribution, which contributes to a reduction in the intersite Coulomb interaction along the stacking and diagonal directions, respectively. Our conjecture is supported by the temperature dependence of the electrical resistivity under the uniaxial strain.
  • Kiyoshi Torizuka, Hiroyuki Tajima, Takashi Yamamoto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (7) 0031-9015 2006/07 [Peer-reviewed]
     Scientific journal 
    We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (x = 1 and 0.75) over a wide temperature range between 4 and 250 K. The electronic contribution can be analyzed particularly below similar to 80 K. A thermal hysteresis depending on the Cu concentration x has been observed between the heating and cooling processes. The system stays in a metallic state when the sample is cooled from room temperature, while a small fraction of insulating islands is created in the metallic state when heated up to room temperature. The insulating islands survive even at high temperatures. This mechanism gives rise to the hysteretic behavior. Heat conduction is sensitive to the difference in the two phases, in contrast with electrical resistivity.
  • T Yamamoto, M Uruichi, K Yakushi, A Kawamoto
    PHYSICAL REVIEW B 73 (12) 1098-0121 2006/03 Scientific journal 
    We present the temperature-dependent infrared and Raman spectra of beta(')-(ET)(3)X-2 (X=HSO4 and ClO4; ET=bis-ethylenedithio-tetrathiafulvalene) compounds which undergo a metal-insulator transition. The infrared-active v(27) mode discontinuously split into two bands at the metal-insulator transition temperature of 127 K in the X=HSO4 salt, whereas, the corresponding mode continuously changed across the metal-insulator transition temperature of similar to 170 K in the X=ClO4 salt. In both compounds, the charge-sensitive v(27) mode split into two in the insulating phase. This drastic spectral change indicates that the metal-insulator transition originated in the charge ordering. Employing the frequencies of the split v(27) bands, the site charges are estimated to be +0.3(4) and +0.8(1) for X=HSO4 and +0.3(6) and +0.8(1) for X=ClO4. We also estimated the site charges using the Raman-active v(2) mode and obtained consistent results. Examining the selection rule of the v(3) mode, we reached the conclusion that the unit cell with space group P1 has a pseudoinversion center in the charge-ordered phase. Based on the symmetry, we propose a charge-ordering pattern for the X=HSO4 and X=ClO4 salts, which is quite different from that of the X=ReO4 salt reported previously. We qualitatively discuss the differences in the charge-ordering pattern considering the anisotropic intersite Coulomb interaction.
  • K. Yakushi, K. Suzuki, K. Yamamoto, T. Yamamoto, A. Kawamoto
    Journal of Low Temperature Physics 142 671 - 674 0022-2291 2006/02 
    Employing Raman spectroscopy, we have studied the electronic structure of the charge-ordering system, Φ-(ET) 2 X, the dihedral angle (ψ) of which ranges from 100 to 121°. The most stable metal, Φ-(ET) 2 I 3 , (ψ = 100°) has a uniform charge distribution in a whole temperature range. The compounds with ψ > 111° have an inhomogeneous charge distribution even above the CO transition, which implies that the charges have localized nature in a whole temperature range. These localized charges are long-range ordered in the CO phase, whereas they are fluctuating randomly or forming short-range ordered domains above the CO phase transition. © Springer Science+Business Media, Inc. 2006.
  • Maki Hiraoka, Hirokazu Sakamoto, Kenji Mizoguchi, Reizo Kato, Tatsuhisa Kato, Tosikazu Nakamura, Kou Furukawa, Koichi Hiraki, Toshihiro Takahashi, Takashi Yamamoto, Hiroyuki Tajima
    JOURNAL OF LOW TEMPERATURE PHYSICS 142 (3-4) 617 - 620 0022-2291 2006/02 [Peer-reviewed]
     Scientific journal 
    The quarter-filled pi band systems, (DMc-DCNQI)(2)M(M = Li1-xCux(x <= 0.14), Ag) were systematically studied with electron paramagnetic resonance (EPR). The intercolumn spin hopping rate D-perpendicular to in Li1-xCux-salt was obtained from the EPR linewidth. The temperature dependence of D, can be understood with the hole soliton model which also explains the DC conductivity. The pi - d mixing of the Cu-salt enhances both D-perpendicular to and sigma(perpendicular to) by 10(3) times more than the Li-salt, which is consistent with the fact that the only Cu-salt has three-dimensional Fermi surface, but that Ag-salt is one-dimensional in spite of the mixing enhancement of D-perpendicular to by 10 times more than the Li-salt.
  • T Yamamoto, M Uruichi, K Yamamoto, K Yakushi, A Kawamoto
    SYNTHETIC METALS 155 (3) 628 - 630 0379-6779 2005/12 Scientific journal 
    The IR and Raman spectra of beta"-(ET)(3)X-2 [X = HSO4 and ClO4] salts were measured at various temperatures below 300 K. The nu(2) and nu(27) modes exhibit the splitting into two peaks below the metal-insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic nu(3L) mode. The assignment of the nu(27) mode of ET+ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO4, (ET)AuCl2Br2 and the isotope analogues. The nu(27) mode is the efficient probe to the site charges of the ET salts. (C) 2005 Published by Elsevier B.V.
  • K Torizuka, H Tajima, Y Kawamura, H Sawa, T Yamamoto
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 (8-9) 1575 - 1578 0022-3697 2005/08 Scientific journal 
    We have measured the thermal conductivity for organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (x = 0, 0.08, and 0.14) over a wide range of temperatures (4 similar to 250 K). A peak can be seen near similar to 20 K. The peak height decreases with decreasing x, and it completely vanishes for x = 0 specimen. This peak is created by a crossover between the phonon mean free path that diverges as T-2 and the phonon specific heat that decreases as T-3. In addition, we have also succeeded in observing the super-lattice patterns of 4k(F) and 2k(F) of (DMe-DCNQI)(2)Li1-xCux (x = 0 and 0.06) accompanied by the Peierls and the spin Peierls transitions by means of the synchrotron radiation X-ray in Tsukuba's Photon Factory. (c) 2005 Elsevier Ltd. All rights reserved.
  • T Yamamoto, M Uruichi, K Yamamoto, K Yakushi, A Kawamoto, H Taniguchi
    JOURNAL OF PHYSICAL CHEMISTRY B 109 (32) 15226 - 15235 1520-6106 2005/08 Scientific journal 
    We reinvestigated the two C=C stretching modes of the five-membered rings of ET (ET = bis(ethylenedithio)tetrathiafulvalene), namely, v(2) (in-phase mode) and v(27) (out-of-phase mode). The frequency of the v(27) mode of ET+ was corrected to be similar to 1400 cm(-1), which was identified from the polarized infrared reflectance spectra of (ET)(ClO4), (ET)((AuBrCl2)-Cl-2) and the deuterium- or C-13-substituted compounds of (ET)(AuBr2Cl2). It was clarified from DFT calculations that the frequency of the v(27) mode of the flat ETO molecule was significantly different from that of the boat-shaped ETO molecule. We obtained the linear relationship between the frequency and the charge on the molecule, rho, for the flat ET molecule, which was shown to be v(27)(rho) = 1398 + 140(1 - rho) cm(-1). The frequency shift due to oxidation is remarkably larger than that reported in previous studies. The fractional charges of several ET salts in a charge-ordered state can be successfully estimated by applying this relationship. Therefore, the v(27) mode is an efficient probe to detect p in the charge-transfer salts of ET. Similarly, a linear relationship for the v(2) mode was obtained as v(2)(rho) = 1447 + 120(1 - rho). This relationship was successfully applied to the charge-poor molecule of theta-type ET salts in the charge-ordered state but could not be applied to the charge-rich molecule. This discrepancy was semiquantitatively explained by the hybridization between the v(2) and v(3) modes.
  • K Yamamoto, T Yamamoto, K Yakushi, C Pecile, M Meneghetti
    PHYSICAL REVIEW B 71 (4) 1098-0121 2005/01 Scientific journal 
    The charge distribution and molecular arrangement of a quarter-filled quasi-one-dimensional system(DI-DCNQI)(2)Ag (DI-DCNQI=2,5-diiodo-dicyanoquinediimine) has been studied by IR and Raman spectroscopy. The charge localization of this material was believed to be a one-dimensional generalization of a Wigner crystal driven by intersite Coulomb repulsion. While charge disproportionation is confirmed via the splitting of b(u) modes in the infrared spectrum, the appearance of intense IR vibronic bands of a(g) modes strongly suggests the presence of the dimerization that is not expected by the proposed 1010 charge ordering model. In addition, the selection rules for the IR and Raman signals cannot be explained without a further symmetry reduction of the unit cell. To explain the vibrational behavior observed for a single crystal, we show that a more appropriate model for the charge ordering is 0110 (2k(F) charge-density wave and 4k(F) bond-order wave).
  • A. F. Bangura, A. I. Coldea, J. Singleton, A. Ardavan, A. Akutsu-Sato, H. Akutsu, S. S. Turner, P. Day, T. Yamamoto, K. Yakushi
    Physical Review B - Condensed Matter and Materials Physics 72 (1) 1098-0121 2005 Scientific journal 
    We report magnetotransport measurements on the quasi-two-dimensional charge-transfer salts β″-(BEDT-TTF)4[(H3O)M(C2O4)3]Y, with Y=C6H5NO2 and C6H5CN using magnetic fields of up to 45 T and temperatures down to 0.5 K. A surprisingly robust superconducting state with an in-plane upper critical field Bc2 33T, comparable to the highest critical field of any BEDT-TTF superconductor, and critical temperature Tcâ 7K is observed when M=Ga and Y=C6H5NO2. The presence of magnetic M ions reduces the in-plane upper critical field to 18T for M=Cr and Y=C6H5NO2 and M=Fe and Y=C6H5CN. Prominent Shubnikov-de Haas oscillations are observed at low temperatures and high magnetic fields, showing that the superconducting salts possess Fermi surfaces with one or two small quasi-two-dimensional pockets, their total area comprising 6% of the room-temperature Brillouin zone the quasiparticle effective masses were found to be enhanced when the ion M was magnetic (Fe or Cr). The low effective masses and quasiparticle densities, and the systematic variation of the properties of the β″-(BEDT-TTF)4[(H3O)M(C2O4)3]Y salts with unit-cell volume points to the possibility of a superconducting groundstate with a charge-fluctuation-mediated superconductivity mechanism such as that proposed by Merino and McKenzie [Phys. Rev. Lett. 87, 237002 (2001)], rather than the spin-fluctuation mechanism appropriate for the κ-(BEDT-TTF)2X salts. © 2005 The American Physical Society.
  • Kiyoshi Torizuka, Hiroyuki Tajima, Takashi Yamamoto
    Physical Review B - Condensed Matter and Materials Physics 71 (19) 1098-0121 2005 Scientific journal 
    We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)2 Li1-x Cux (0≤x≤0.14) over a wide temperature range between 4 and 250 K. We observed the phonon contribution in the whole range measured. A phonon peak was observed near ∼20 K. This peak denotes a crossover between the phonon mean free path that diverges as T-2 and the phonon specific heat that decreases as T3. The peak height decreases with the reduction of Cu concentration x and vanishes in the x=0 sample. We discuss this behavior in terms of the spin-Peierls local lattice distortion. © 2005 The American Physical Society.
  • Takashi Yamamoto, Mikio Uruichi, Kyuya Yakushi, Jun-Ich Yamaura, Hiroyuki Tajima
    Physical Review B - Condensed Matter and Materials Physics 70 (12) 1 - 125102 0163-1829 2004/09 Scientific journal 
    We present the infrared and Raman spectra of β″-(BEDT-TTF) 3(ReO4)2 (BEDT-TTF=bis-ethylenedithio- tetrathiafulvalene) measured at various temperatures. We investigated the three C=C stretching modes, ν2ν27, and ν3. The infrared and Raman spectra discontinuously changed at 80 K. Below 80 K, for example, the doublet ν2 bands split into three peaks, the doublet ν27 also split into three, and a mutual exclusion rule for the vibronic ν3 modes in the infrared and Raman spectra was broken. This symmetry lowering was consistent with the result of x-ray crystal structure analyses conducted at 100 K and 22 K. The site charges in the unit cell estimated from the splitting of ν2 were +0.73,+0.7 3, and +0.53 in the metallic phase, and they were +0.2, +0.85, and +0.95 in the insulating phase. The metal-insulator transition of this compound was characterized as the charge-ordering transition originated from the localization of charge due to Coulomb interactions.
  • T Yamamoto, K Yakushi, Y Shimizu, G Saito
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 (8) 2326 - 2332 0031-9015 2004/08 Scientific journal 
    The polarized Raman and infrared spectra of theta-(ET)(2)CU2CN[N(CN)(2)](2) [ET = bis(ethylenedithio)tetrathiafulvalene] were measured at various temperatures below 300K. We investigated the three C=C stretching modes, V-2, V-3 and V-27. The spectral pattern is compatible with the horizontally charge-ordered state, where the site-charge distributions are +0.1(7) and +0.8(3). We have found that the vibronic V-3 bands correlate to the dihedral angles, psi, in the theta-ET salts. This relation is well reproduced by the numerical calculation based on the cluster model with C-2 symmetry. The spectral features suggest the dynamical fluctuation of nearly localized charges even above its phase transition temperature, similar to220 K.
  • T Hatsui, T Yamamoto, H Tajima, N Kosugi
    CHEMICAL PHYSICS 298 (1-3) 189 - 193 0301-0104 2004/03 [Peer-reviewed]
     Scientific journal 
    Cu L-2,L-3-edge X-ray absorption spectra for (Me-2-DCNQI)(2)Li1-xCux alloys (Me-2-DCNQI: 2,5-dimethyl-N,N-1-dicyanoquinone-diimine) were measured in order to investigate the local electronic structure around Cu atoms. Both in the Cu L-3- and U-edge regions. (Me-2-DCNQI)(2)Cu (x = 1) shows a characteristic band higher in energy than the lowest sharp band associated with the transitions to the Cu 3d hole, on the other hand, K3Cu(CN)(4) with Cu 3d(10) configuration shows only the higher-energy band. These higher-energy bands arise from the transitions to the lowest unoccupied molecular orbitals of Me2-DCNQI and CN ligand molecules, respectively.. where the intensity comes from the Cu 3d components through strong hybridization between metal and ligand. The spectral feature does not change even if the x value is reduced to less than 0.1, indicating that the alloys have nearly the same covalent bond between Cu and Me-2-DCNQI as (Me-2-DCNQI)(2)Cu (x = 1), independent of the substitution. This demonstrates that we can control the filling and the dimensionality of electronic structure in Me2-DCNQI charge-transfer complexes through the replacement of Li by Cu. (C) 2003 Elsevier B.V. All rights reserved.
  • T. Yamamoto, M. Uruichi, K. Yakushi, Jun-Lchi Yamaura, H. Tajima, A. Kawamoto
    Journal De Physique. IV : JP 114 397 - 399 1155-4339 2004 International conference proceedings 
    We studied C=C stretching bands of β"-(ET)3(ReO 4)2 and β"-(ET)4M(CN) 4H2O (M=Pt, Pd and Ni) at the low temperatures below 300 K in order to verify the inhomogeneous charge distributions. A drastic spectral change was observed for β"-(ET)3(ReO4) 2 at 80 K, below which the system falls into the charge ordered state. On the other hand, a continuous spectral change was observed for β"-(ET)4Ni(CN)4H2O and β"-(ET)4Pd(CN)4H2O. v2 for M=Ni and Pd exhibited a doublet, suggesting an inhomogeneous charge distributions. v2 for M=Pt did not show a peak splitting, while C=C bands for the deuterium analogue exhibited a behaviour similar to those for M=Ni. © EDP Sciences.
  • T Yamamoto, H Tajima, R Kato, M Uruichi, K Yakushi
    SYNTHETIC METALS 133 291 - 292 0379-6779 2003/03 Scientific journal 
    We measured thermoelectric power and Raman spectra for (Me(2)DCNQI)(2)CuxLi1-x. The v(8) (quinoid C=N stretch) Raman line shifts downwards with an increase of copper contents (x), and exhibits a split for x less than or equal to 0.24. Temperature dependence of the thermoelectric power exhibits drastic change between x = 0.14 and x = 0.22. This behaviour is consistent with the phase diagram previously determined. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Kawamoto, M Ashizawa, T Mori, T Yamamoto, JI Yamaura, H Tajima
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 (12) 3059 - 3064 0031-9015 2002/12 Scientific journal 
    Low-temperature crystal structure and optical properties of the quasi-one-dimensional organic conductor (ChTM-TTP)(2)GaCl4 (ChTM-TTP: 2-[4,5-(1,2-cyclohexylenedithio)-1,3-dithiol-2-ylidene]-5[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) have been investigated. As the temperature lowers, the disordered anion transforms to an ordered state with a superstructure wave vector of q = (1/2, 0, 1/2). The peak intensities of the superlattice gradually increase in the metallic region, and are saturated below 150 K; this indicates that the charge localization below 150 K is independent of the evolution of the superlattice. The reflectance spectra of (ChTM-TTP)(2)X suggest the existence of moderate interchain interactions. The transverse interactions are more pronounced in the GaCl4 salt (t(perpendicular to)/t(parallel to) approximate to 1/7) than the AuBr2 and Au(CN)(2) Salts. The low-temperature optical reflectance of the GaCl4 salt shows no significant change, indicating that (ChTM-TTP)(2)GaCl4 goes to an insulating state with a small charge gap, which is consistent with the transport property. The low-frequency peak in the chain-axis optical conductivity is attributed to a correlation gap, though the expected on-site Coulomb repulsion U is relatively small.
  • T Yamamoto, H Tajima, R Kato, M Uruichi, K Yakushi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 (8) 1956 - 1964 0031-9015 2002/08 Scientific journal 
    Raman spectra of (Me-2-DCNQI)(2)CuxLi1-x (0 less than or equal to x less than or equal to 1) have been measured at room temperature, 200 K, 100 K and 5 K. The observed Raman hands are assigned on the basis of the vibrational analysis done by Lunardi and Pecile. The Raman band assigned to the a(g)v(R8) fundamental mode (quinoid C=N stretching) shifts downward with an increase of x and exhibits a remarkable split for 0 less than or equal to x less than or equal to 0.29. This frequency shift is attributable to the change of a charge density on a Me-2-DCNQI molecule. From the split of the v(R8) Raman band, it is concluded that the charge densities on Me-2-DCNQI molecules are not equivalent even at room temperature for 0 less than or equal to x less than or equal to 0.29.
  • H Yoshino, T Konoike, K Murata, GC Papavassiliou, T Sasaki, T Yamamoto, H Tajima
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 376 171 - 176 1058-725X 2002 Scientific journal 
    The electric resistivity was measured for tau- (EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1-y) (1), tau-(EDO-S,S-DMEDT-TTF)(2)- (I-3)(1-y)(2) and tau-(P-S,S-DMEDT-TTF)(2)(AuBr2)(1+y) (3), (ysimilar to0.75) under hydrostatic pressure and magnetic field. Pressure increases the M-I transition temperature of (2) and (3). The period of the angular dependence of the magnetoresistance of (1) at 5 T changes from 90degrees to 180degrees by pressure of 5 kbar, while that of (2) and (3) is not changed.
  • T Konoike, A Oda, K Iwashita, T Yamamoto, H Tajima, H Yoshino, K Ueda, T Sugimoto, K Hiraki, T Takahashi, T Sasaki, Y Nishio, K Kajita, GC Papavassiliou, GA Mousdis, K Murata
    SYNTHETIC METALS 120 (1-3) 801 - 802 0379-6779 2001/03 [Peer-reviewed]
     Scientific journal 
    Magnetoresistance, magnetization, and reflectance spectra were measured for tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+gamma) (gamma similar to0.75) (EDO-S,S-DMEDT-TTF = ethylenedioxy-S,S-dimethylethylenedithio-tetrathiafulvalene) and tau-(P-S,S-DMEDT-TTF)(2)(AuBr2)(1+gamma), (gamma similar to0.75) (P-S,S-DMEDT-TTF = pyrazino-S,S-dimethylethylenedithio-tetrathiafulvalene). The saturation of magnetization curve and Drude dispersion imply the weak ferromagnetic and metallic nature of former compound at low temperature. For the comparison with this compound, magnetoresistance of latter salt was measured up to 24 T.
  • T Yatamoto, N Hanasaki, J Yamaura, S Aonuma, H Tajima, K Yakushi, M Uruichi, R Kato
    SYNTHETIC METALS 120 (1-3) 873 - 874 0379-6779 2001/03 Scientific journal 
    We report two studies for (DMe-DCNQI)(2)Li1-xCux recently carried out by our group. In the first study, we report the measurements of electrical resistivity, magnetic susceptibility, reflectance spectra for (DMe-DCNQI)(2)Li1-xCux. The point of this study is that the x-T phase diagram of the system can be divided into three categories, i. e., 0 less than or equal to x less than or equal to 0.14, 0.17 less than or equal to x less than or equal to 0.3, 0.3 less than or equal to x less than or equal to 1.0. In the second study, we report the results of the electrical resistivity measurements for (DMe-DCNQI)(2)Cu under the uni-axial pressure applied parallel and perpendicular to the stacking axis of DMe-DCNQI (c-axis).
  • T Naito, T Inabe, K Takeda, K Awaga, T Akutagawa, T Hasegawa, T Nakamura, T Kakiuchi, H Sawa, T Yamamoto, H Tajima
    JOURNAL OF MATERIALS CHEMISTRY 11 (9) 2221 - 2227 0959-9428 2001 Scientific journal 
    An electrolysis of bis(ethylenedithio)tetrathiafulvalene (ET) and a Mn-cluster in a 1,1,2-trichloroethane solution containing 10% (vol/vol) of ethanol yields black lustrous single crystals, beta"-(ET)(3)(MnCl4)(1,1,2-C2H3Cl3) based on the X-ray structural study. The crystal structure can be characterized as alternating two-dimensional donor sheets and insulating sheets made of isolated [MnCl4](2-) ions and the 1,1,2-C2H3Cl3 molecules. Every pair of the neighbouring donor molecules has a large displacement along both short and long molecular axes. A tight-binding band calculation suggests that this arrangement should lead to a weak but isotropic intermolecular interaction in the donor sheets, and this in turn should lead to a marginally metallic or semiconducting electronic structure. Although the polarized reflectance spectra and the temperature-dependent spin susceptibility derived from the EPR spectra on the single crystal indicate metallic nature, the electrical behaviour under atmospheric pressure is semiconductive with room temperature conductivity of 35 S cm(-1) and apparent activation energy of 0.023 eV. It exhibits a resistive hump with hysteresis at around 60 K, which could be associated with a structural transition demonstrated by a series of low temperature X-ray oscillation photographs. The magnetic susceptibility at 4.5-300 K does not exhibit any anomaly and is well reproduced by the Curie-Weiss model with Curie constant C/emu K mol(-1) = 3.89 and Weiss temperature theta /K = -0.10. This magnetic behaviour can be quantitatively understood as the sum of Pauli paramagnetism of the pi -electrons and the contribution from the local spins on the Mn(II) ions with d(5)-configuration S = 5/2). High pressure easily suppresses the increase in resistivity at low temperature, and the electrical behaviour is particularly sensitive to the first 3-5 kbar.
  • T Kawamoto, T Mori, T Yamamoto, H Tajima, Y Misaki, K Tanaka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 (12) 4066 - 4070 0031-9015 2000/12 Scientific journal 
    (TTM-TTP)AuI2 (TTM-TTP: 2,5-bis[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetra-thiapentalene) has it dimerized structure along the donor stacking direction. and shows semiconducting behavior below room temperature. ESR, static magnetic susceptibility, and optical reflectance of this salt hare been measured to investigate the spin state and the electronic correlation. The ESR signal. has been observed from room temperature to 3 K, and the spin susceptibility shows paramagnetic behavior with a rapid decrease below 10 K. The static magnetic susceptibility is paramagnetic and has an anomaly around 10 K in agreement with the ESR result. The chain axis optical reflectance spectra show clear optical gap in the mid-infrared region. An: attempt is undertaken to analyze the optical spectrum by means of the one-dimensional dimerized Hubbard model, which suggests that the on-site Coulomb repulsion, U, is small and the spin polarization is located at the marginal paramagnetic boundary. These results indicate that this compound is not a band-insulator but the Mott insulator with a small spin gap.
  • T Yamamoto, H Tajima, R Kato
    SOLID STATE COMMUNICATIONS 114 (5) 281 - 284 0038-1098 2000 Scientific journal 
    We measured the static spin susceptibility of the quasi-one-dimensional molecular conductors, (DMe-DCNQI)(2)Li1-xCux (0 less than or equal to x less than or equal to 1). We separated the susceptibility component due to itinerant electrons from that due to local magnetic moments by assuming that the temperature dependence of the latter component obeys the Curie-Weiss law. From the temperature dependence of the former component, we conclude that the ground state of this system is nonmagnetic for x less than or equal to 0.14 and paramagnetic For 0.17 less than or equal to x. The phase boundary thus determined is consistent with the phase diagram already determined by resistivity measurements. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • T. Kawamoto, M. Ashizawa, M. Aragaki, T. Mori, T. Yamamoto, H. Tajima, H. Kitagawa, T. Mitani, Y. Misaki, K. Tanaka
    Physical Review B - Condensed Matter and Materials Physics 60 4635 - 4645 0163-1829 1999/12 
    The compounds (TTM-TTP)(I 3 ) 5/3 and (TSM-TTP)(I 3 ) 5/3 which have polyiodide chains along the donor stacking direction and show characteristic "copper" luster, exhibit metallic behavior above T MI ≈20 K. High-pressure resistivity, the Raman spectra, and optical reflectance of these salts have been measured to investigate the origin of the low-temperature insulating state and the iodine species. For (TSM-TTP)(I 3 ) 5/3 two kinds of conducting behavior have been observed; below 20 K some low-conducting samples have shown an increase of the resistivity of more than 10 3 times, but other high-conducting samples have shown an increase of less than 10 times. The increase of resistivity is almost suppressed under a pressure of 11.5 kbar in the high-conducting phase of (TSM-TTP)(I 3 ) 5/3 . The Raman spectra provide clear evidence that the polyiodide chain is composed of I 3 - in these compounds. The Raman spectra and the x-ray photographs indicate that the increase of resistivity originates in the disorder. The chain axis optical reflectance spectra show plasma edges appearing in the infrared region and three peaks from the infrared to the visible range; the latter originate from the intramolecular transition and polyiodide ions. Temperature dependence of optical conductivity is metallic even below T MI . From these results, the origin of the low-temperature insulating state is attributed to disorder driven localization. ©1999 The American Physical Society.
  • H Tajima, T Yamamoto, J Yamaura, S Aonuma, R Kato
    SYNTHETIC METALS 103 (1-3) 2193 - 2194 0379-6779 1999/06 Scientific journal 
    We systematically study transport and optical properties of charge-transfer salts, (DMe-DCNQI)(2)Li1-xCux (0 less than or equal to x less than or equal to 1). In the optical studies, we found the two absorption bands, one attributable to collective excitations associated with 4k(F) CDW (A-band) and the other to single-particle excitations across the Peierls gap (B-band). The intensity of the former band is almost constant for x less than or equal to 0.29 and steeply increases for x greater than or equal to 0.39. The latter band appears around 3000 cm(-1) for 0 less than or equal to x less than or equal to 0.14, and shifts downward for x greater than or equal to 0.17.
  • T Yamamoto, H Tajima, JI Yamaura, S Aonuma, R Kato
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 (4) 1384 - 1391 0031-9015 1999/04 Scientific journal 
    We systematically study transport and optical properties of charge-transfer sails, (Me(2)DCNQI)(2)Li1-xCux (0 less than or equal to x less than or equal to 1). The temperature dependence of electrical resistivity exhibits semiconducting behavior at x = 0, a metal-semiconductor transition for 0.08 less than or equal to x less than or equal to 0.20, and metallic behavior down to 4.2K for x greater than or equal to 0.39. A semiconductor-semiconductor transition is observed around 60K for x less than or equal to 0.14. The reflectance spectra at room temperature reveal tno optical excitations in the infrared region. The first excitation appears in salts with x not equal 0 far below 650 cm(-1) The second excitation is the so-called mid-infrared band, which appears around 3000 cm(-1) for 0 less than or equal to x less than or equal to 0.14, and shifts downward for x greater than or equal to 0.17. We propose a hypothesis which provides an explanation both for the metallic conduction and for the mid-infrared band in a one-dimensional conductor having a quarter-filled band.

Books etc

  • Advances and Applications in Energy Storage and Conversion: Chapter 2: Diversity in the Electronic Phase due to Interchange of MO Levels in [M(dmit)2] Anion Salts (M = Pd and Pt) in Functional Materials (p83-p155)
    Takashi Yamamoto (Single work, Chapter 2)
    Pan Stanford Publishing Pte. Ltd. 2018/10 9780429468131 73 83-155
  • 物理化学実験法
    山本 貴 (Contributor, 固体の電気伝導)
    東京化学同人 2011/09

Conference Activities & Talks

  • Hidden Ordered States Characteristic of Interchange of MO Levels in Molecule-Based Conductors  [Invited]
    YAMAMOTO Takashi
    The Toyota Riken International Workshop: Organic Semiconductors, Conductors, and Electronics  2018/10
  • κ‒(ET)2Cu[N(CN)2]Iの圧力下電気抵抗  [Not invited]
    嵐 育未, 山本 貴, 内藤俊雄, 小西健介
    第12回分子科学討論会2018福岡  2018/09
  • Interplay between spin, charge, lattice and orbital in molecule-based frustrated spin system  [Not invited]
    Takashi Yamamoto, Toshio Naito, Yasuhiro Nakazawa, Masafumi Tamura, Kyuya Yakushi, Reizo Kato
    43rd International Conference on Coordination Chemistry  2018/08
  • κ型(ET)2Cu[N(CN)2]I塩の物性と二次元電子構造  [Not invited]
    山本貴, 中村祐介, 内藤俊雄
    日本物理学会 第73回年次大会  2018/03
  • HOMO-LUMO逆転した二次元系に特有な磁性と電荷の協奏現象  [Not invited]
    山本 貴, 内藤 俊雄, 藤本 尚史, 中澤 康浩, 田村 雅史, 池本 夕佳, 森脇 太郎, 薬師 久弥, 加藤 礼三
  • 新規π縮小型TTP系ドナーの合成とカチオンラジカル塩の構造と物性  [Not invited]
    白旗 崇, Mohamad Safuwan, bin Alias, 木下 直哉, 古田 圭介, 山本 貴, 内藤 俊雄, 山田 順一, 御崎 洋二
    第11回分子科学討論会  2017/09
  • 振動分光によるMe4N[Pt(dmit)2]2およびMe4P[Pd(dmit)2]2の分子非対称化の研究  [Not invited]
    山本 貴, 高杉 滉, 内藤 俊雄, 加藤 礼三
    第11回分子科学討論会  2017/09
  • β´´-型ET塩の一軸性圧縮実験III  [Not invited]
    沖井優一, 山本貴, 内藤俊雄, 圷広樹, 中澤康浩
    日本物理学会 第72回年次大会  2017/03
  • 振動領域時間分解分光から見たMe4P[Pt(dmit)2]2の光誘起ダイナミクス  [Not invited]
    石川忠彦, 卜澤陽平, 田中誠一, 恩田健, 沖本洋一, 腰原伸也, 山本貴, 野村光城, 加藤礼三
    日本物理学会 第72回年次大会  2017/03
  • κ-(ET)2Cu[N(CN)2]Iの伝導性・磁性における異常性  [Not invited]
    山本 貴, 中村 祐介, 内藤 俊雄, 松下 幸一郎, 中澤 康浩, 小西 健介
    日本化学会第97春季年会  2017/03
  • 「分子固体物性における分子間距離の役割」  [Not invited]
    YAMAMOTO Takashi
    Workshop on Materials Science under Ultra-High Pressure MATSUYAMA 2017  2017/03
  • κ-(ET)2Cu[N(CN)2]Iにおけるポンプ プローブ時間分解分光測定  [Not invited]
    土屋聡, 児玉匠, 中村祐介, 山本貴, 内藤俊雄, 戸田泰則
    日本物理学会 2016年秋季大会  2016/09
  • k-(ET)2Cu[N(CN)2]Iの複雑な超伝導挙動  [Not invited]
    中村 祐介, 山本 貴, 内藤 俊雄, 小西 健介
    第10回分子科学討論会  2016/09
  • β″-型ET塩における一軸性圧縮実験  [Not invited]
    沖井 優, 山本 貴, 内藤 俊雄, 小西 健介, 圷 広樹, 中澤 康浩
    第10回分子科学討論会  2016/09
  • Uniaxial Strain Effects on β"-type BEDT-TTF salts  [Not invited]
    OKII, Yuichi, YAMAMOTO, Takashi, NAITO, Toshio, KONISHI, Kensuke
    日本化学会第96春季年会  2016/03
  • k—(ET)2Cu[N(CN)2]Iの多様な物性  [Not invited]
    中村 祐介, 山本 貴, 内藤 俊雄, 小西 健介
    第9回分子科学討論会  2015/09
  • 圧力下超伝導体β-ET塩およびβ″-ET塩の電荷整列状態に対する異方的圧力効果  [Not invited]
    山本貴, 沖井優一, 内藤俊雄, 大西功二, 中澤康浩
    日本物理学会 2015年秋季大会  2015/09
  • 高い光伝導を示すNMQ[Ni(dmit)2]の伝導機構に関する研究  [Not invited]
    長山 直樹, 小原 敬士, 山本 貴, 内藤 俊雄
    日本化学会第95春季年会  2015/03
  • 光照射によって不対電子の局在性が変わる銅(II)ジチオレン錯体塩の電気・磁気挙動  [Not invited]
    野間 博貴, 小原 敬士, 山本 貴, 内藤 俊雄
    日本化学会第95春季年会  2015/03
  • 時間分解電子線回折によるMe4P[Pt(dmit)2]2における光誘起構造変化ダイナミクスの直接観測II  [Not invited]
    石川忠彦, 塩沼健太, 沖本洋一, 恩田健, 腰原伸也, Stuart A. Hayes, Sercan Keskin, Gaston Corthey, 羽田真毅, Kostyantyn Pichugin, Alexander Marx, R.J, Dwayne Miller, Wawrzyniec Kazub, Maciej Lorenc, 山本貴, 野村光城, 崔亨波, 加藤礼三
    日本物理学会 第70回年次大会  2015/03
  • 軌道準位が逆転する分子性固体X[M(dmit)2]2における遠隔的相互作用  [Not invited]
    山本 貴, 内藤 俊雄, 田村 雅史, 加藤 礼三, 薬師 久弥, 中澤 康浩, 池本 夕佳, 森脇 太郎
    第8回分子科学討論会  2014/09
  • Charge Fluctuation in the Antiferromagnetic  [Not invited]
    YAMAMOTO Takashi
    International Conference on Science and Technology of Synthetic Metals (ICSM 2014).  2014/07
  • κ-(BETS)2FeBr4の超伝導状態の熱的研究  [Not invited]
    福岡脩平, 山下智史, 中澤康浩, 山本貴, 藤原秀紀
    日本物理学会 第69回年次大会  2014/03
  • 反強磁性を示す分子性導体の分子振動分光  [Not invited]
    山本貴, 藤本尚史, 内藤俊雄, 加藤礼三, 森脇太郎B, 池本夕佳
    日本物理学会 第69回年次大会  2014/03
  • 時間分解電子線回折によるMe4P[Pt(dmit)2]2における光誘起構造変化ダイナミクスの直接観測  [Not invited]
    石川忠彦, 沖本洋一, 恩田健, 腰原伸也, Stuart Hayes, Sercan Keskin, Gaston Corthey, Masaki Hada, Kostyantyn Pichugin,R.J, Dwayne Miller, Wawrzyniec Kazub, Maciej Lorenc, 山本貴, 野村光城, 加藤礼三
    日本物理学会 第69回年次大会  2014/03
  • 高輝度赤外光で分かる分子性導体の電子状態  [Invited]
    山本 貴
    第27回日本放射光学会年会  2014/01
  • 分子固体の電気抵抗測定に適した異方的弱圧印加法  [Not invited]
    山本貴, 渡邊あかり, 山下智史, 中澤康浩
    日本物理学会 2013年秋季大会  2013/09
  • π-d系分子性導体BETS塩の低温電子状態  [Not invited]
    福岡脩平, 山下智史, 中澤康浩, 藤原秀紀, 山本貴, 白旗崇, 高橋かず子
    日本物理学会 2013年秋季大会  2013/09
  • 二量体化したユニットをもつ分子性導体における動的電荷不均一性の研究  [Not invited]
    山本貴, 大西功二, 松下幸一郎, 中澤康浩, 加藤礼三, 池本夕佳, 森脇太郎, 薬師久弥
    日本物理学会 2013年秋季大会  2013/09
  • Me4P[Pt(dmit)2]2 における光励起応答ダイナミクスの観測  [Not invited]
    進藤泰貴, 細田亮介, 石川忠彦, 恩田健, 沖本洋一, 腰原伸也, 野村光城, 加藤礼三, 山本貴, Alain Moreac, Wawrzyniec Kaszub, Maciej Lorenc
    日本物理学会 2013年秋季大会  2013/09
  • “Experimental study on the mechanism of the charge frustration in the molecular superconductors”  [Not invited]
    T. Yamamoto, Y. Nakazawa, M. Tamura, K. Yakushi, R. Kato
    10th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM 2013)  2013/07
  • 分子性導体の電荷整列と電荷揺らぎの研究  [Invited]
    山本 貴
    日本物理学会 第68回年次大会  2013/03
  • κ-BEDT-TTF塩のラマン分光  [Not invited]
    薬師久彌, オルガ・ドロズドバ, 清水康弘, 斎藤軍治, 河本充司, 山本貴
    日本物理学会 第68回年次大会  2013/03
  • 光学スペクトルから見たX[Pt(dmit)2]2(X=Me4P, Me4Sb)における電荷分離相転移  [Not invited]
    石川忠彦, 恩田健, 沖本洋一, 腰原伸也, 野村光城, 加藤礼三, 山本貴, Alain Moreac, Wawrzyniec Kaszub, Maciej Lorenc
    日本物理学会 第68回年次大会  2013/03
  • 日本物理学会 第68回年次大会  [Not invited]
    福岡脩平,山下智史,山本貴,中澤康浩,藤原秀紀,白旗崇,高橋かず子  2013/03
  • κ-型ET塩における電荷不均一性の起源  [Not invited]
    山本貴, 松下幸一郎, 中澤康浩, 薬師久弥
    日本物理学会 2012年秋季大会  2012/09
  • κ-(BEDT-TTF)2Cu2CN3のラマンスペクトル  [Not invited]
    薬師久彌, オルガドロズドバ, 清水康弘, 斉藤軍治, 河本充司, 山本貴
    日本物理学会 2012年秋季大会  2012/09
  • 面内磁場下におけるκ-(BETS)2FeX4(X=Cl, Br)の熱的研究  [Not invited]
    福岡脩平, 山下智史, 山本貴, 中澤康浩, 藤原秀紀, 白旗崇, 高橋かず子, 小林速男, 小林昭子
    日本物理学会 2012年秋季大会  2012/09
  • 圧力下超伝導体β″-(ET)2(ReO4)の電荷整列状態の観測  [Not invited]
    大西 功二, 山本 貴, 中澤 康浩
    第6回分子科学討論会  2012/09
  • 分子性固体を対象とした、弱圧印加装置の開発  [Not invited]
    渡邊 あかり, 山本 貴, 山下 智史, 中澤 康浩
    第6回分子科学討論会  2012/09
  • (DMe-DCNQI)2Liにおける電流電圧特性の異方性  [Not invited]
    木俣基, 林義之, 田島裕之, 山本貴, 加藤礼三
    日本物理学会 2012年秋季大会  2012/09
  • ET3X2の電荷整列相における光誘起相転移ダイナミクス  [Not invited]
    石川忠彦, 馬上一樹, 深澤直人, 恩田健, 沖本洋一, 腰原伸也, 大西功二, 山本貴, 中澤康浩
    日本物理学会 2012年秋季大会  2012/09
    YAMAMOTO Takashi
    The International Conference on Science and Technology of Synthetic Metals 2012 (ICSM 2012)  2012/07
  • [Pd(dmit)2]塩における特異な分子軌道効果  [Not invited]
    山本 貴, 中澤 康浩, 田村 雅史, 藥師 久彌, 加藤 礼三
    日本化学会第92春季年会  2012/03
  • 振動スペクトルから見たX[Pd(dmit)2]2の光誘起相転移  [Not invited]
    石川忠彦, 田中貴裕, 深澤直人, 沖本洋一, 恩田健, 腰原伸也, 長谷川巧, 宇田川眞行, 山本貴, 田村雅史, 加藤礼三
    日本物理学会 第67回年次大会  2012/03
  • π-d系有機導体κ-(BETS)2FeX4(X=Cl, Br)の磁場下熱容量測定  [Not invited]
    福岡脩平, 山本貴, 中澤康浩, 白旗崇A, 高橋かず子, 小林速男, 小林昭子
    日本物理学会 第67回年次大会  2012/03
  • Chemical Approach to Inducing Charge Fluctuation  [Invited]
    YAMAMOTO Takashi
    MDF International Workshop: Open-shell Organic Molecules. –Synthesis and Electronic Structure Freedom–  2011/10
  • “Rich variety in the ground states of [Pd(dmit)2]2 salts, and the methodology for analysing intra-dimer interactions, inter-dimer interactions and MO levels”  [Not invited]
    T. Yamamoto, Y. Nakazawa, M. Tamura, K. Yakushi, R. Kato
    9th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM 2011)  2011/09
  • 応力下磁化測定法の開発及び、低圧下抵抗測定法の開発  [Not invited]
    渡邊 あかり, 大西 功二, 山本 貴, 中澤 康浩
    第5回分子科学討論会2011  2011/09
  • κ-(BEDT-TTF)2Cu[N(CN)2]Iの赤外・ラマンスペクトル  [Not invited]
    松下 幸一郎, 山本 貴, 中澤 康浩, 売市 幹大, 薬師 久弥
    第5回分子科学討論会2011  2011/09
  • (DMe-DCNQI)2Liの非線形伝導と磁気抵抗II  [Not invited]
    木俣基, 林義之, 田島裕之, 山本貴
    日本物理学会 2011年秋季大会  2011/09
  • 振動分光学的手法による[Pd(dmit)2]塩の分析法  [Not invited]
    山本 貴, 中澤 康浩, 田村 雅史, 加藤 礼三, 薬師 久弥
    第5回分子科学討論会2011  2011/09
  • 有機超伝導体β"-型BEDT-TTF塩の電荷に起因する空間不均一性  [Not invited]
    村岡 佑樹, 山本 貴, 中澤 康浩, 森脇 太郎, 池本 夕佳
    第5回分子科学討論会2011  2011/09
  • 金属挙動を示す[Pd(dmit)2]塩の赤外スペクトル  [Not invited]
    山本貴, 中澤康浩, 薬師久弥, 崔亨波, 加藤礼三
    日本物理学会 第66回年次大会  2011/03
  • キラル金属磁性錯体の磁場下熱容量測定  [Not invited]
    福岡脩平, 山本貴, 中澤康浩, 東川大志, 井上克也
    日本物理学会 第66回年次大会  2011/03
  • κ-型有機超伝導体の圧力下熱容量測定  [Not invited]
    村岡佑樹, 段田麻佑, 山本貴, 中澤康浩
    日本物理学会 第66回年次大会  2011/03
  • 時間分解分子振動分光法を用いたEt2Me2Sb[Pd(dmit)2]2完全電荷分離相における光誘起現象の解明  [Not invited]
    深澤直人, 石川忠彦, 沖本洋一, 腰原伸也, 山本貴, 田村雅史, 加藤礼三, 恩田健
    日本物理学会 第66回年次大会  2011/03
  • (DME-DCNQI)2Liの低温電気伝導測定  [Not invited]
    林義之, 木俣基, 田島裕之, 山本貴
    日本物理学会 第66回年次大会  2011/03
  • Pd(dmit)2塩中のスピン液体における顕著な重水置換効果  [Not invited]
    山下智史, 山本貴, 中澤康浩, 加藤礼三
    日本物理学会 2010年秋季大会  2010/09
  • ナフタレンジイミド誘導体と擬一次元臭素架橋鉛錯体からなる分子性導体の物性と電子状態  [Not invited]
    井口弘章, 高石慎也, 久保和也, 宮坂等, 山下正廣, 山本貴, 田中久暁, 黒田新一, 田嶋陽子, 加藤礼三
    日本物理学会 2010年秋季大会  2010/09
  • 高分解能赤外顕微分光から見た、スピン液体および電荷揺らぎの実態  [Not invited]
    山本 貴, 村岡 佑樹, 吉元 諒, 中澤 康浩, 森脇 太郎, 池本 夕佳, 圷 広樹, 圷, 佐藤) あかね, Peter Day, 薬師 久弥
    第4回分子科学討論会2010  2010/09
  • β″-(ET)4[Ga(C2O4)3](H3O)PhNO2の空間不均一性  [Not invited]
    吉元 諒, 山本 貴, 中澤 康浩, 森脇 太郎, 池本 夕佳, 圷 広樹, 圷 あかね, Day Peter
    第4回分子科学討論会2010  2010/09
  • β″-(ET)4Pt(CN)4H2Oの相分離の可視化  [Not invited]
    村岡 佑樹, 山本 貴, 中澤 康浩, 森脇 太郎, 池本 夕佳
    第4回分子科学討論会2010  2010/09
  • 時間分解分子振動分光によるEt2Me2Sb[Pd(dmit)2]2の超高速光誘起現象の探索  [Not invited]
    深澤 直人, 石川 忠彦, 沖本 洋一, 腰原 伸也, 山本 貴, 田村 雅史, 加藤 礼三, 恩田 健
    第4回分子科学討論会2010  2010/09
  • “Fluctuations around the Quantum Critical Point of Tightly Dimerized Molecular Conductors”  [Not invited]
    T. Yamamoto, Y. Muraoka, R. Yoshimoto, S. Yamashita, Y. Nakazawa, Y. Ikemoto, T. Moriwaki, R. Kato, K. Yakushi
    International Conference on Science and Technology of Synthetic Metals. (ICSM 2010)  2010/07
  • κ-(BETS)2FeBr4の熱容量の磁場印加方向依存性  [Not invited]
    福岡脩平, 山本貴, 中澤康浩, 小林速男, 小林昭子
    日本物理学会 第65回年次大会  2010/03
  • 微小チップによるダイマー型Mott絶縁体の熱容量測定  [Not invited]
    村岡佑樹, 山下智史, 山本貴, 中澤康浩
    日本物理学会 第65回年次大会  2010/03
  • スピン液体的挙動を示す分子性固体の電荷および格子の揺らぎ  [Not invited]
    山本貴, 吉元諒, 村岡佑樹, 山下智史, 中澤康浩, 森脇太郎, 池本夕佳, 加藤礼三, 田村雅史, 薬師久弥
    日本物理学会 第65回年次大会  2010/03
  • EtMe3Sb[Pd(dmit)2]2の低温熱容量  [Not invited]
    山下智史, 山本貴, 中澤康浩, 西尾豊, 田村雅史, 加藤礼三
    日本物理学会 2009年秋季大会  2009/09
  • Charge Fluctuation of the Superconducting Molecular Crystals  [Not invited]
    YAMAMOTO Takashi
    The 8th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM2009)  2009/09
  • 水素結合由来の構造揺らぎを持つ有機固体における磁気秩序と電荷秩序  [Not invited]
    山本 貴, 加藤 礼三, 中澤 康浩, 薬師 久弥, メジール セシール, バタイユ パトリック
    日本化学会第89春季年会  2009/03
  • 多様な基底状態を取る[Pd(dmit)2]塩の分光学的研究  [Not invited]
    山本 貴, 山下 智史, 中澤 康浩, 田村 雅史, 加藤 礼三, 薬師 久弥
    第2回分子科学討論会  2008/09
  • 分子性化合物単結晶の圧力下熱容量  [Not invited]
    所 のぞみ, 窪田 統, 山下 智史, 山本 貴, 中澤 康浩
    第2回分子科学討論会  2008/09
  • ニ次元三角格子構造をもつ電荷移動塩のスピン液体状態の熱的研究  [Not invited]
    山下 智史, 山本 貴, 中澤 康浩, 鹿野田 一司, 田村 雅史, 加藤 礼三
    第2回分子科学討論会  2008/09
  • [Pd(dmit)2]塩における二量体内電荷分離現象の発見  [Not invited]
    山本 貴, 加藤 礼三, 田村 雅史, 福永 武男, 薬師 久弥
    日本化学会第88春季年会  2008/03
  • (ET)3(AuBr2)2(AuBr4)2における電荷不均化状態と金属的導電性  [Not invited]
    坂田雅文, 前里光彦, 齋藤軍治, 山本貴, 薬師久弥, S.S. Khasanov, N.G. Spitsina, A.D. Dubrovskii, E.B. Yagubskii, P. Deplano, M.L. Mercuri
    日本物理学会 第63回年次大会  2008/03
  • Technique for anisotropic extension of molecular crystals: Application to organic superconductors  [Not invited]
    YAMAMOTO Takashi
  • Charge Ordering State of ET, BETS and [Pd(dmit)2] Salts by Temperature-Dependent Vibrational Spectroscopy  [Not invited]
    YAMAMOTO Takashi
    International Conference on Science and Technology of Synthetic Metals, (ICSM 2006)  2006/07


  • 分子結晶におけるスピン液体の起源を解明
    山本 貴  共同プレスリリース 愛媛大学 理化学研究所 JASRI/SPring-8  2017  Report research institution
  • 「分子内振動で電子移動を制御する」
    山本 貴  パリティ  31-  45  -47  2016  [Peer-reviewed][Invited]
     Introduction commerce magazine
  • 「分子が変形する様子を2兆分の1秒刻みでコマ撮り撮影 -光機能性物質の動作メカニズム解明に成功-」
    石川忠彦, 腰原伸也, スチュアート・ヘイズ, ドウェイン・ミラー, 加藤礼三, 山本貴  共同プレスリリース 東京工業大学JST  2015  Report research institution
  • 固体物理 トピックス欄,「分子性導体の電荷整列と超伝導転移」
    山本 貴  固体物理  44-  237  -255  2009  [Invited]
     Introduction commerce magazine
  • 「電荷の不均一状態がキッカケとなる超伝導現象を有機材料で発見」
    山本 貴  理化学研究所 プレスリリース  2008  Report research institution
  • “New clues on organic superconductors”
    YAMAMOTO Takashi  RIKEN Research highlights  3-  5  2008  [Invited]
     Technical report

Industrial Property Rights

  • 山本 貴, 加藤 礼三, 高橋 一郎, 山澤 建二  独立行政法人理化学研究所  201303085543023284
  • 山本 貴, 加藤 礼三, 高橋 一郎, 山澤 建二  独立行政法人理化学研究所  200903035468035050

Awards & Honors

  • 2012/10 日本物理学会 若手奨励賞
    受賞者: 山本 貴
  • 2011/08 公益信託分子科学奨励森野基金 公益信託分子科学奨励森野基金
    受賞者: 山本 貴
  • 2008/03 日本化学会 若手講演賞
    受賞者: 山本 貴
  • 2008/01 特定領域(分子性導体) チャレンジャー賞
    受賞者: 山本 貴

Research Grants & Projects

  • 軌道・電荷・スピン自由度が共存する分子固体の研究
    Date (from‐to) : 2015/04 -2019/03 
    Author : 山本 貴
  • 分子性超伝導体における揺らぎの普遍性と動的組成比の解明
    Date (from‐to) : 2012/04 -2015/03 
    Author : 山本 貴
  • 有機単結晶界面のデバイス機能と物性の開拓
    Date (from‐to) : 2010/04 -2012/03 
    Author : 竹谷 純一
  • 複合環境制御下での熱測定による有機π電子系の研究
    Date (from‐to) : 2010/04 -2012/03 
    Author : 中澤 康浩
  • 分子性固体における電荷整列状態と超伝導の研究および新しい応力発生法の開発
    Date (from‐to) : 2011 -2011 
    Author : 山本 貴
  • 脆弱な分子凝縮体の延伸下物性及び、電荷整列・有機超伝導の新展開
    Date (from‐to) : 2008/04 -2009/03 
    Author : 山本 貴
  • 分子性導体に対する負圧誘起相転移の研究
    Date (from‐to) : 2005/04 -2007/03 
    Author : 山本 貴
  • 分子性結晶素子を目指した試料加工、物性測定の研究
    Date (from‐to) : 2001/04 -2002/03 
    Author : 田島 裕之
  • 無機有機複合系における、光・磁場・電場を用いた伝導電子制御の研究
    Date (from‐to) : 2000/04 -2001/03 
    Author : 田島 裕之
  • 分子性導体におけるキャリアドーピング効果の研究
    Date (from‐to) : 1999/04 -2001/03 
    Author : 山本 貴

Social Contribution

  • Workshop on Materials Science under Ultra-High Pressure MATSUYAMA 2017
    Date (from-to) : 2017/03-2017/03
    Role : Planner
    Sponser, Organizer, Publisher  : 愛媛大学 超高圧材料研究ユニット
    Event, Program, Title : Workshop on Materials Science under Ultra-High Pressure MATSUYAMA 2017
  • 日本物理学会 2015年秋季大会 運営委員
    Date (from-to) : 2015/09-2015/09
    Role : Planner
    Sponser, Organizer, Publisher  : 日本物理学会
    Event, Program, Title : 日本物理学会 2015年秋季大会
  • 日本物理学会 第70回年次大会 運営委員
    Date (from-to) : 2015/03-2015/03
    Role : Planner
    Sponser, Organizer, Publisher  : 日本物理学会
    Event, Program, Title : 日本物理学会 第70回年次大会
  • 第4回分子科学討論会 運営委員
    Date (from-to) : 2010/09-2010/09
    Role : Organizing member
    Sponser, Organizer, Publisher  : 分子科学会
    Event, Program, Title : 第4回分子科学討論会

Media Coverage

  • 結晶中の分子が集団変形 「スピン液体」起源解明
    Date : 2017/10/27
    Publisher, broadcasting station: 科学新聞社
    Program, newspaper magazine: 科学新聞




  • 2019, the first semester, under graduate, 物理化学Ⅱ
  • 2019, the first semester, under graduate, 卒業研究Ⅰ
  • 2019, the first semester, under graduate, 物理化学演習

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