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

DOI： 10.7566/jpsj.91.034707

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

We have found that the electrical properties of an organic charge transfer salt are qualitatively affected by slight differences in the conformation of one of the ethylene groups, which is not involved in the conduction pathways.

DOI： 10.1039/d1ma00933h

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

DOI： 10.7566/jpsj.90.114704

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

DOI： 10.7566/jpsj.90.063708

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

In this study, to investigate the electronic state of organic molecular crystal kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I (kappa-1), polarized pump probe spectroscopy was conducted. From the observation of photoinduced carrier relaxation dynamics, we found that the carrier dynamics in kappa-I are qualitatively different from those in other kappa-type salts and inhomogeneous electronic states are realized in the single crystal. As temperature decreases, the transient polarization anisotropy along the c axis associated with a charge order develops below T-MI = 40K, which is consistent with the metal insulator transition observed in the resistivity measurement. Moreover, we found the position where the transient polarization anisotropy is enhanced along the 1/2 (a + c) direction. Remarkably, this signal shows no clear changes at T-MI = 40 K; instead, it shows an anomalous increase in the signal amplitude at T similar to 8 K. A possible origin of this anomaly is the locally induced superconducting state.

DOI： 10.7566/jpsj.89.064712

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

DOI： 10.7566/jpsj.89.034709

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

DOI： 10.1039/C9TC00491B

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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.

DOI： 10.1038/s41598-017-13118-4

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DOI： 10.3390/magnetochemistry3020020

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

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.

DOI： 10.7566/JPSJ.86.014706

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

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.

DOI： 10.7566/JPSJ.85.104711

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

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.

DOI： 10.1103/PhysRevB.93.245136

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

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.

DOI： 10.1126/science.aab3480

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DOI： 10.7566/JPSJ.84.084711

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

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

DOI： 10.11316/jpsgaiyo.70.1.0_1519

CiNii Books

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

DOI： 10.11316/jpsgaiyo.70.2.0_1633

CiNii Books

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

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.

DOI： 10.7566/JPSJ.83.053703

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

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.

DOI： 10.1007/s10973-013-3015-5

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

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.

DOI： 10.1021/jp403193a

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publisher：MDPI AG  

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.

DOI： 10.3390/cryst2030893

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

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.

DOI： 10.1002/pssb.201100685

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.tca.2011.02.001

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

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

DOI： 10.1002/pssc.201100640

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

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.80.123709

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

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) Omega.cm(-1), E-a = 97 meV) at ambient pressure and as an insulator at 1.7 GPa (rho(1.7GPa) = 4.5 Omega.cm(-1), E-a = 76 meV). Magnetic measurements indicated that the [Mn-2](2+) units in 1 behaved as S-T = 4 SMMs at low temperatures.

DOI： 10.1021/ic200863c

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

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.

DOI： 10.1143/JPSJ.80.074717

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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.

DOI： 10.1038/ncomms1274

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

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.

DOI： 10.1088/1742-6596/320/1/012027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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

DOI： 10.1016/j.physb.2009.11.059

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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

DOI： 10.1016/j.physb.2009.12.053

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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 0 T 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 (C) 2010 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2009.02.002

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

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.

DOI： 10.1021/ic800176q

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

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.

DOI： 10.1143/JPSJ.77.024714

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DOI： 10.1103/PhysRevB.77.205120

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

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.

DOI： 10.1063/1.2777191

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

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.

DOI： 10.1103/PhysRevB.75.205132

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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.

DOI： 10.1143/JPJS.75.074604

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

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.

DOI： 10.1103/PhysRevB.73.125116

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Employing Raman spectroscopy, we have studied the electronic structure of the charge-ordering system, theta-(ET)(2)X the dihedral angle (phi) of which ranges from 100 degrees to 121 degrees. The most stable metal, theta-(ET)(2)I-3, (phi=100 degrees) has a uniform charge distribution in a whole temperature range. The compounds with phi > 111 degrees 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.

DOI： 10.1007/s10909-006-9112-0

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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.

DOI： 10.1007/s10909-006-9103-1

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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.

DOI： 10.1016/j.synthemt.2005.08.016

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

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.

DOI： 10.1021/jp050247o

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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.

DOI： 10.1016/j.jpcs.2005.05.060

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

We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (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 similar to 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 T-3. 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.

DOI： 10.1103/PhysRevB.71.193101

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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).

DOI： 10.1103/PhysRevB.71.045118

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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.

DOI： 10.1103/PhysRevB.72.014543

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We present the infrared and Raman spectra of beta"-(BEDT-TTF)(3)(ReO4)(2) (BEDT-TTF=bis-ethylenedithio-tetrathiafulvalene) measured at various temperatures. We investigated the three C=C stretching modes, nu(2),nu(27), and nu(3). The infrared and Raman spectra discontinuously changed at 80 K. Below 80 K, for example, the doublet nu(2) bands split into three peaks, the doublet nu(27) also split into three, and a mutual exclusion rule for the vibronic nu(3) 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 nu(2) were +0.7(3),+0.7(3), and +0.5(3) in the metallic phase, and they were +0.2,+0.8(5), and +0.9(5) 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.

DOI： 10.1103/PhysRevB.70.125102

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

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.

DOI： 10.1143/JPSJ.73.2326

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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.

DOI： 10.1016/j.chemphys.2003.11.023

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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.

DOI： 10.1016/j.prp.2004.03.007

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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.

DOI： 10.1016/S0379-6779(02)00313-2

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The electric resistivity was measured for τ- (EDO-S,S-DMEDT-TTF) 2(AuBr2)1+y (1), τ-(EDO-S,S-DMEDT-TTF) 2- (I3)1+y (2) and τ-(P-S,S-DMEDT-TTF) 2(AuBr2)1+y (3), (y∼0.75) 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 90° to 180° by pressure of 5 kbar, while that of (2) and (3) is not changed.

DOI： 10.1080/10587250210722

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

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.

DOI： 10.1143/JPSJ.71.3059

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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.

DOI： 10.1143/JPSJ.71.1956

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

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).

DOI： 10.1016/S0379-6779(00)01471-5

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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.

DOI： 10.1016/S0379-6779(00)01022-5

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DOI： 10.1016/S0379-6779(00)00826-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

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.

DOI： 10.1039/b102786g

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(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.

DOI： 10.1143/JPSJ.69.4066

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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.

DOI： 10.1016/S0038-1098(00)00033-8

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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.

DOI： 10.1103/PhysRevB.60.4635

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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.

DOI： 10.1016/S0379-6779(98)00883-2

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

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.

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J-GLOBAL

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Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

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

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CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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Language：Japanese   Publisher：一般社団法人 日本物理学会  

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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Language：Japanese   Publisher：一般社団法人 日本物理学会  

CiNii Books

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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

CiNii Books

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

CiNii Books

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

CiNii Books

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Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.1.4.0_820_3

CiNii Books

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J-GLOBAL

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J-GLOBAL

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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DOI： 10.1016/S0379-6779(02)00741-5

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

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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Language：Japanese   Publisher：一般社団法人日本物理学会  

CiNii Books

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

CiNii Books

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

CiNii Books

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

CiNii Books

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Language：Japanese   Publishing type：Book review, literature introduction, etc.  

The immune system must remain tolerant to self-antigens so as not to destroy what it has evolved to protect. There appears several mechanism for this purpose
deletion, anergy, sequestration of autoantigen and active suppression. These mechanism cooperate, constituting a fail-safe system, although the strategy against each autoantigen is determined by the nature of the autoantigen, i.e., the amount, timing and location of the expression. Here, we review and discuss on the pathogenesis of autoimmune disease as a consequence of the breakdown of the surveillance network, based on the recent advances in immunology.

Scopus

PubMed

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

CiNii Books

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

CiNii Books

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

CiNii Books

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

Under ambient pressure, the cation radical salt (TMET-STF)(2)BF4, where the tight-binding band calculation suggests coexistence of one- and two-dimensional Fermi surfaces associated with two different conduction layers within the crystal, shows two types of resistivity anomalies around 115 and 13 K, followed by a superconducting transition at 4.1 K(onset).

DOI： 10.1039/a700629b

Web of Science

Scopus

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

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