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

We investigate bulk superconductivity in a high-quality single crystal of Bi2Pd (beta-Bi2Pd; space group: I4/mmm) with a superconducting transition temperature of 5.4 K, by exploring its electrical resistivity, magnetic susceptibility, and specific heat. The temperature dependence of the electrical resistivity shows convex-upward behavior at temperatures greater than 40-50 K, which can be explained using a parallel-resistor model. In addition, the temperature dependences of the upper critical magnetic field and the specific heat suggest that beta-Bi2Pd is a multiple-band/multiple-gap superconductor.

DOI： 10.1143/JPSJ.81.113708

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We demonstrate a photo-induced insulator-to-metal (I-M) transition in an organic linear chain compound (TMTSF)(2)PF6 [bis-(tetramethyl-tetraselenafulvalene)hexafluorophosphate] in the spin-density-wave (SOW) ground state by optical pump and terahertz probe experiments We observe the collapse of SOW gap in the optical conductivity spectrum at 3 ps after the photo-excitation indicating the ultrafast I-M transition in the SOW system Temporal evolution of the terahertz reflectivity change shows that the photo-induced metallic state sustains longer than 400 Ps (C) 2009 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2009.10.063

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In the title compound we made X-ray satellite reflection measurements up to 0 7 GPa and angle-dependent magnetoresistance (AMR) measurements at 1 9 GPa The purpose of the study is to clarify (1) how large the temperature-pressure regime is for the long-range charge ordering (CO) (2) whether or not the high pressure regime for the superconductivity is really a metallic state and (3) what the electronic properties are in the intermediate pressure regime between the long-range CO and the superconducting states The long-range CO was found to be stable up to 0 7 GPa and its temperature-pressure regime coincides with that expected from transport measurements AMR at 1 9 GPa 1 4K and 12T suggests the presence of Fermi surfaces consistent with band calculations based on X-ray structural analyses at room temperature and the same pressure Raman studies by one of the authors (K Y) suggest the presence of metallic state in the intermediate pressure regime where the resistance shows apparently insulating properties Discussion is made on the role of the charge-degree of freedom in causing the superconductivity (C) 2009 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2009.11.092

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We studied the low-temperature electrical properties of the two-dimensional organic conductor beta ''-(BEDT-TTF)(2)AuBr2, whose electronic structure is similar to that of the pressure-induced superconductor beta ''-(DODHT)(2)PF6 having a charge-ordered transition at 255 K at ambient pressure. We found that the ground state of beta ''-(BEDT-TTF)(2)AuBr2 at ambient pressure has a charge-density-wave phase below 6.5 K accompanied by x-ray superlattice spots. We also discovered superconductivity in the vicinity of the charge-density-wave phase by applying uniaxial strain. Based on the obtained results, we propose a unified electronic phase diagram that suggests the relationships among the charge-ordered insulating state, the superconducting phase, and the charge-density-wave phase in beta ''-type organic conductors. The phase diagram shows that the superconducting phase is located near the charge-density-wave phase, which suggests that spin fluctuations play a minor role in the mechanism of the superconductivity and sheds light on the possibility of charge-fluctuation-mediated superconductivity in this type of organic conductor.

DOI： 10.1103/PhysRevB.81.024519

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We investigated the effects of hydrostatic pressure and uniaxial strain on the spin-Peierls (SP) transition of an organic radical magnet, benzo[1,2-d:4,5-d']bis[1,3,2]dithiazole(BBDTA)center dot InCl4. It has a one-dimensional coordination polymer structure along its c-axis and its SP transition occurs at 108 K. The SP transition temperature T-SP decreased to 99K at a hydrostatic pressure of 10 kbar, while it increased to 132 K at a uniaxial strain along the c-axis of 8 kbar. The pressure dependences of T-SP under these two conditions were discussed by evaluatingg two parameters, namely, the intrachain interaction 2J/k(B) and the effective spin-lattice coupling parameter eta, that are related to T-SP by the equation T-SP = 1.6 eta J/k(B). Under ambient pressure, the a- and c-axes of this material shortened monotonically with decreasing temperature, while the b-axis elongated below T-SP. In this study, we found the correlation between eta and the change in the lattice constant b. 2J/k(B) increased with increasing hydrostatic pressure and uniaxial strain, suggesting that the contraction along the c-axis does not depend on the manner of pressurization. From the evaluation of eta, the observed variation in T-SP is explained by the difference between the changes in b under the two pressurization conditions.

DOI： 10.1143/JPSJ.78.124705

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Photoexcited dynamics of a spin-density-wave (SDW) state in an organic linear-chain compound bis-(tetramethyl-tetraselenafulvalene)hexafluorophosphate, (TMTSF)(2)PF6, is investigated by optical pump and terahertz probe experiments. After the ultrashort laser-pulse excitation, a sudden closing followed by a recovery of the SDW gap is clearly observed in the far-infrared spectrum. The recovery time is found to diverge toward the phase-transition temperature, T-SDW, while the gap remains open at T-SDW. The observed critical slowing down behavior is interpreted in terms of three-dimensional fluctuation which enlarges near the phase-transition temperature.

DOI： 10.1103/PhysRevB.80.220408

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We perform crystal structure analyses of the organic conductor alpha-(BEDT-TTF)(2)I-3 [where BEDT-TTF denotes bis(ethylene)dithiotetrathiafulvalene] and its selenium analogue alpha-(BEDT-TSeF)(2)I-3 [where BEDT-TSeF denotes bis(ethylene)dithiotetraselenafulvalene] at room temperature under hydrostatic pressure, where they are expected to have zero-gap points at the Fermi level with a Dirac-cone-type dispersion for a massless particle. We calculate the electronic band structures using a combination of the extended Huckel molecular orbital calculation based on the obtained crystal structures and the tight-binding band structure calculation. We find that I) the obtained Fermi surfaces of both salts under hydrostatic pressure are simply larger than those at ambient pressure owing to an increase in overlap integrals caused by the pressure, and II) electronic structures having zero-gap points with a Dirac-cone-type dispersion at the Fermi level are realized only in alpha-(BEDT-TTF)(2)I-3 by the introduction of suitable site potentials in wide parameter areas. These results suggest that, to realize such a unique electronic structure in this class of materials, some mechanisms are needed to effectively give the site potentials employed in this study. Examples are electronic correlation effects and I-3 anion potentials.

DOI： 10.1143/JPSJ.78.114714

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

We report on a development of the reflection-type terahertz time-domain spectroscopy system and apply it to determine the conductivity spectra of the spin density wave (SDW) ground states in (TMTSF)(2)PF6. We take special care over optimizing the spatial resolution of the measurement system in order to investigate the tiny sample and also for correcting the phase error of the measurement. We observe a distinct reduction of the optical conductivity below similar to 65 cm(-1), which is a clear indication of SDW gap formation with metal-insulator transition. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200879900

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We investigate the low-temperature electronic phase of a two-dimensional organic conductor, (BEDT-TTF)(2)CsCd(SCN)(4) [where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene], which has a large hump between 32 and around 5 K in the temperature dependence of the interlayer resistance. We present experimental results for the temperature dependence of the resistance under magnetic fields and its Kohler plots, and an x-ray diffraction study. We find that I) Kohler's rule is strongly violated below 32 K, although the rule is valid above 32 K, and II) weak superlattice spots appear at 15.6 K in the x-ray study. On the basis of the experimental results, we suggest that the origin of the resistance hump is the formation of a possible charge density wave transition at about 32 K by the nesting of a pair of large one-dimensional Fermi surfaces obtained in the electronic structure calculation based on the crystal structure at room temperature.

DOI： 10.1143/JPSJ.77.063702

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The superconductivity in a quasi-two-dimensional organic conductor, beta"-(DODHT)(2)PF(6) salt, which is expected to appear after the melting of a charge ordering (CO) state, has been examined using an extended Hubbard model with anisotropy for both the transfer energies and the nearest-neighbor repulsive interactions between the DODHT molecules. The fluctuation is treated by the random phase approximation based on mean-field calculation of the CO. When pressure is applied, an insulating state with CO (COI) changes into a metallic state with weakened CO (COM) at an intermediate pressure, and a normal state without CO emerges at higher pressures. For the COM state at intermediate pressure, the COI state and the normal state also exist as metastable states, and their free energies are nearly the same within a narrow energy range of 10(-3) eV. Thus these three states may coexist with each other by forming a phase separation at finite temperature. We find that the spin fluctuation around such a mean-field COM state gives rise to a superconducting state with a full gap. Further, we suggest that d-wave superconductivity mediated by the charge fluctuation occurs in the normal state with a quasi-one-dimensional Fermi surface when the nearest-neighbor interaction becomes as large as the on-site interaction.

DOI： 10.1088/0953-8984/20/12/125205

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We developed the uniaxial elongation method to elongate a soft crystalline sample along one desired direction. An epoxy rod which contains a sample passes through a stainless steel ring along its diameter and is fixed to the ring. The external force is applied to the ring along the direction perpendicular to the epoxy rod to deform the ring and elongate the epoxy rod, leading to the elongation of the sample in the rod. We verify this method by using a strain gauge instead of a sample. The results of resistance measurements of two kinds of quasi-one-dimensional conductors, NbSe3 and (TMTSF)(2)ClO4(TMTSF denotes tetramethyltetraselenafulvalene.), are also presented as the examples of this experimental technique.

DOI： 10.1143/JPSJ.76.114710

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We performed the crystal structure analyses of the pressure-induced organic superconductor ss"-(DODHT)(2)PF6 (DODHT denotes (1,4-dioxane-2,3-diyldithio)dihydrotetrathiafulvalene) at the hydrostatic pressures of 0.75GPa and 1.9GPa in order to investigate the key parameter for inducing the superconductivity. At ambient pressure, ss"-(DODHT)(2)PF6 undergoes an insulator-to-insulator transition at 255 K accompanied by charge ordering. By applying pressure, this charge-ordering transition is suppressed and superconductivity is generated at around 3 K above 1.32 GPa. Using the obtained atomic coordinates, we estimated the transfer integrals t and intermolecular nearest-neighbor Coulomb interaction energies V between conduction electrons and found that one of V/vertical bar t vertical bar ratios perpendicular to charge-ordering stripes plays an important role in suppressing the charge-ordering phase.

DOI： 10.1143/JPSJ.76.034709

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Non-ohmic transport was studied by pulse method in the charge-ordered state of the organic conductor theta-(BEDT-TTF)(2)CsZn(SCN)(4) as controlling the electronic state by uniaxial strain method. It was discovered that the non-ohmic conduction under high electric fields lead to the meta-stable state with a structural modification, where the ohmic resistance was reduced to be smaller than the original. The response of the CO state to pulsed electric fields suggested a possible internal deformation of the ordered charge's lattice.

DOI： 10.1143/JPSJ.76.033703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The results are reported of the pressure (P) dependence of the electrical resistance (R), the thermoelectric power (Seebeck effect) (S), and compressibility as well as the time dependence of R at fixed P up to 20 GPa for four metallo-organics based on the BEDT-TTF (bisethylenedithiolo-tetrathiofulvalene) group, theta-(BEDT-TTF)(2)CsZn(SCN)(4), alpha-(BEDT-TTF)(2)I-3, beta'-(BEDT-TTF)(2)PF6, and (BEDT-TTF)-TCNQ. X-ray powder and single-crystal diffraction studies were also made on theta-(BEDT-TTF)(2)CsZn(SCN)(4) at high pressures up to P similar to 10 GPa. The R values of all the crystals decreased with pressure up to P similar to 3-5 GPa (low-pressure regime), and then the sign of dR/dP inverted (high-pressure regime). From the investigation of the mechanical and structural properties, these materials were found to have a large compressibility in the low-pressure regime, and a small one in the high-pressure region. In theta-(BEDT-TTF)(2)CsZn(SCN)(4) we observed pressure-induced reversible degradation (amorphization) in structure without a solid-phase reaction. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200672530

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We report unique resistance behavior around the superconducting transition of a quasi-two-dimensional organic superconductor, beta '''-(DODHT)(2)PF6 [DODHT = (1,4-dioxane-2,3-diyldithio)dihydrotetrathiafulvalene]. When the superconductivity appears, the interlayer resistance begins to decrease at a temperature higher than that for the intralayer resistance. Both resistances show a step-like decrease toward zero resistance. These unique phenomena are possibly related to the unique structural properties of the salt.

DOI： 10.1143/JPSJS.76SA.186

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High-pressure studies on organic conductors and superconductors are reviewed. It is stressed that almost all the organic conductors are studied by means of high pressures, but the role or meaning of pressure effect has been dependent on the salts and physics of interests. In organic molecular crystals, many intriguing physical phenomena such as the appearance of charge- and spin-density-waves, superconductivity, Mott insulator and charge ordering have been found. The application of hydrostatic and uniaxial pressures plays an essential role for understanding the nature of these electronic states, for guiding the material design, and for creating the unexpected quantum states as well as high-T-c superconductivities. This review includes the history, pressure techniques, and works under conventional pressures of up to 1.5 GPa, ultra-high pressures up to 10 GPa as well as uniaxial pressure, but the topics which are dealt with in this same special issue are not covered.

DOI： 10.1143/JPSJ.75.051015

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DOI： 10.1021/ja060979+

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In order to investigate the relationships between crystal structures and electronic properties of theta-type BEDT-TTF organic conductors, electrical properties of theta-(BEDT-TTF)(2)Ag(CN)(2) and theta-(BEDT-TTF)(2)CsZn(SCN)(4) and crystal structures of theta-(BEDT-TTF)(2)CsZn(SCN)(4) tinder uniaxial strain are investigated. The resistivity measurements for both salts tinder uniaxial strain show that the intercolumnar uniaxial strain preserves the metallic nature while the infra-columnar one induces an insulating behavior, which are reminiscent of the charge-ordered state of theta-(BEDT-TTF)(2)RbZn(SCN)(4). Structure analyses of theta-(BEDT-TTF)(2)CsZn(SCN)(4) under uniaxial strain indicate that the inter-columnar strain slightly increases the diagonal transfer integral but does not vary the vertical one. and the infra-columnar uniaxial strain largely increases the vertical transfer integral but does not change the diagonal one. Based on these experimental results, the key parameters to determine the electrical properties of theta-type BEDT-TTF salts are discussed. It is suggested that the transfer integral along the infra-columnar direction dominates the occurence of the charge-ordered state.

DOI： 10.1143/JPSJ.75.044716

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In order to investigate relationships between superconducting phase and charge ordered one, the uniaxial strain method is applied to the superconducting salt alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) and the organic conductor alpha-(BEDT-TTF)(2)CSCd(SCN)(4). Both salts preserve metallic states under a-axial strain and show insulating behaviours under c-axial strain. These results suggest that i) c-axial strain controls the electronic properties of the a-type salts, and ii) the insulating state in the vicinity of the superconducting phase of alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) is a charge ordered phase, as expected from the comparison in the lattice parameters with the charge ordered salt theta-(BEDT-TTF)(2)RbZn(SCN)(4).

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We carried out Se-77 NMR measurements on BETS2(Cl(2)TCNQ) under pressure in order to investigate the magnetic properties of the insulating state which appears above 0.6 GPa. The relaxation rate 1/T-1 at 0.7 GPa shows small peak-like anomaly at 20 K, indicating a spin density wave transition as observed in BETS2(Br(2)TCNQ).

DOI： 10.1007/s10909-006-9201-0

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Magneto-transpon properties of the newly prepared layer-structured organic conductor beta"-(BEDT-TTF)(2)CsCd(SCN)(4) are investigated. Temperature dependence of the interlayer resistance without magnetic fields shows a hump-like anomaly between 32 K and 5 K at ambient pressure. Measurements of the Shubnikov-de Haas oscillations indicate that the electronic structure at low temperature is different from that calculated from the crystal structure at room temperature. Under magnetic fields parallel to the layer, magnetic field dependence of the interlayer resistance also shows a large dip-like anomaly below 32 K, where the hump-like anomaly starts to appear. We suggest that the hump-like anomaly of beta"-(BEDT-TTF)(2)CsCd(SCN)(4) is a density wave transition accompanied by nesting of its one dimensional Fermi surfaces, and that the dip-like anomaly in the magneto-resistance is ascribed to magnetic field dependence of the interlayer hopping of electrons.

DOI： 10.1088/1742-6596/51/1/076

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Structural and electronic properties of a new BEDT-TTF based radical cation salt, alpha-(BEDT-TTF)(2)CsCd(SCN)(4), are presented. In the measurements of the electrical resistivity and the magnetic susceptibility, this new a-type salt shows metallic behavior down to low temperature. Measurements of the resistivity under in-plane c-axial strain reveal a newly observed insulating phase, suggesting that alpha-(BEDT-TTF)(2)CsCd(SCN)(4) is placed near an insulating phase which might have close relationships with a superconducting phase realized in a-type salts. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2006.01.025

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For the purpose of crystal structure analysis under uniaxial strain at low temperatures, we developed a pressure cell for uniaxial compression and a unique design of an x-ray diffractometer wherein both the x-ray source and the detector are capable of two-axial rotation with a fixed sample. This arrangement is advantageous to crystal structure analyses under extreme conditions that require a large and heavy apparatus. Using the present diffractometer, we performed the crystal structure analyses of the organic conductor, alpha-(BEDT-TTF)(2)I-3 (BEDT-TTF denotes bis(ethylene)dithio-tetrathiafulvalene), under uniaxial strain and ambient pressure, and at room and low temperatures, and obtained results that were qualitatively consistent with those of resistivity measurements. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2001607

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Using the uniaxial strain method, the lattice parameters and the atomic positions of the quasi-two-dimensional organic conductor theta-(BEDT-TTF)(2)CsZn(SCN)(4) were measured at room temperature with piston pressures up to 10 kbar applied parallel to the c-axis in the conducting plane. The lattice parameter c was predominantly reduced with increasing the piston pressure although a small Poisson's effect occurred in the parameter a. Band calculation showed that the transfer integrals under the uniaxial compression by the piston pressure of 10 kbar became similar to those of theta-(BEDT-TTF)(2) RbZn(SCN)(4). This result is consistent with that of transport measurements reported already and suggests that a charge disproportionation, which has been observed in the RbZn-compound, occurs also in the present compound under the uniaxial compressive strain. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cap.2004.01.004

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C-13 NMR measurements were carried out to investigate the electronic state of Mixed-stack organic charge-transfer complex (BEDO-TTF)(Cl(2)TCNQ). From the remarkable temperature dependence of the central shift and relaxation rate, we have confirmed that the transition at 110 K is from paramagnetic to nonmagnetic spin-singlet phase.

DOI： 10.1051/jp4:2004114033

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In order to investigate relationships between the crystal structure and electronic properties, crystal structure analyses of alpha-(BEDT-TTF)(2)I-3 were performed under in-plane uniaxial strains. It is known that, at ambient pressure, this salt has a semimetallic electronic structure having hole and electronic pockets, and undergoes a metal-insulator transition at 135 K due to a charge disproportionation on BEDT-TTF molecules. Present structure analyses showed that the sizes of both hole and electron like pockets on the Fermi surface rather decreased under a-axial strain, while those of hole ones increased under b-axial strain. These results are qualitatively consistent with observed behaviors of the metal-insulator transition under uniaxial strains.

DOI： 10.1051/jp4:2004114123

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DOI： 10.1016/S0379-6779(02)01037-8

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DOI： 10.1016/S0379-6779(02)00338-7

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DOI： 10.1016/S0921-4534(02)02760-0

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DOI： 10.1016/S0379-6779(02)00336-3

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DOI： 10.1080/10587250290101397

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DOI： 10.1080/10587250210805

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Low-temperature electronic properties of the first all-organic donor-acceptor-type superconducting system, (BETS)(2)(X(2)TCNQ) [X=Cl, Br] under high pressure have been investigated by means of resistivity and H-1 NMR experiments. The crystal structure of this class of complexes is characterized by a twin-columnar structure of BETS without intra-columnar dimerization at room temperature. Pressure-temperature phase diagrams are established for these compounds, where the electronic ground status are spin-density-wave (SDW's) insulators, except a narrow, region of superconducting state in (BETS)(2)(Cl(2)TCNQ). A possible unified picture of the electronic states of the title compounds is discussed in terms of hydrostatic pressure effects and chemical substitution ones on them.

DOI： 10.1143/JPSJ.70.3023

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Observation and characterization are reported on a neutral-ionic (NI) phase transition under pressure in (BEDT-TTF)(ClMeTCNQ), which is a mixed-stack charge-transfer compound with BEDT-TTF-based intercolumnar networks. Optical and electrical experiments revealed that the compound undergoes a pressure-induced NI transition at 1 GPa at room temperature. The temperature-pressure phase diagram of this phase transition was established by the electrical resistivity measurements at low temperature under pressure. The observed symmetry breaking in the infrared spectra and dramatic decrease of resistivity indicate that the NI transition in (BEDT-TTF)(ClMeTCNQ) at 1 GPa at room temperature is qualitatively similar in nature to that in the standard material (TTF)(CA). In contrast, the NI transition in (BEDT-TTF)(ClMeTCNQ) at low temperature under lower pressure considerably differs from that in (TTF)(CA) as to the resistivity behaviors around the phase boundary: The former becomes almost continuous without showing any anomaly, while the latter is significantly discontinuous. We discuss the origin of the observed electrical behaviors in (BEDT-TTF)(ClMeTCNQ) in terms of the effect of intercolumnar interaction associated with BEDT-TTF moieties.

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H-1 and Se-77 NMR measurements have been performed to clarify the electronic properties of charge transfer complexes, (BETS)(2)(X(2)TCNQ) (X = Cl and Br). In the CI,TCNQ complex, a Korringa-like relaxation behavior has been observed in the metallic state at ambient pressure. At 6.5 kbar, where a metal-insulator (M-I) transition is induced, a sign of anitiferromagnetic ordering was observed in the insulating state at 10 K. In the Br(2)TCNQ complex, we have also found that Se-77-1/T-1 forms a peak around the M-I transition temperature and that NMR line is broadened in the insulating state. The nature of the insulating states of both compounds seem to be the same, (C) 2000 Elsevier Science Ltd. All rights reserved.

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DOI： 10.1016/S0379-6779(00)00543-9

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DOI： 10.1016/S0379-6779(00)00897-3

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Systematic uniaxial strain studies of (formula presented) (formula presented) have been carried out. By controlling the in-plane lattice parameters a and c independently, we find that both compounds have essentially the same phase diagram in electronic properties, although, under the hydrostatic pressures, they show quite different phase diagrams. The K salt shows the superconductivity like (formula presented) salt under the c-axis uniaxial strain, and the latter undergoes a transition to the density-wave state like the former under the a-axis uniaxial strain. These changes in electronic structures are verified by measuring the angle-dependent magnetoresistance. The electronic properties of these compounds can be systematically understood as a function of (formula presented) the ratio of the in-plane lattice parameters. © 2001 The American Physical Society.

DOI： 10.1103/PhysRevB.64.155104

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DOI： 10.1103/PhysRevB.64.155104

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DOI： 10.1016/S1567-1739(00)00014-6

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DOI： 10.1016/S1567-1739(01)00029-3

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DOI： 10.1016/S0379-6779(00)00691-3

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DOI： 10.1016/S0379-6779(00)01178-4

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DOI： 10.1016/S0379-6779(00)01104-8

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DOI： 10.1002/1521-3951(200101)223:1<97::AID-PSSB97>3.0.CO;2-M

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DOI： 10.1016/S0379-6779(00)00536-1

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We report synthesis and examination of the electronic properties of an isomorphous series of mixed-stack organic charge-transfer complexes, composed of [bis(ethylenedithio) tetrathiafulvalene] (BEDT-TTF)-based electron donors and electron accepters of halogen-substituted tetracyanoquinodimethanes (TCNQ's). Single crystals of (BEDT-TTF)(Me,TCNQ), (BEDT-TTF)(CIMeTCNQ), and (BEDO-TTF)(Cl(2)TCNQ) were investigated as to their crystal structures, and optical and magnetic properties. The intermolecular overlaps between the stacked columns were comparable to the face-to-face overlap between the donor and the acceptor molecules inside the stacks. As seen from the optical and magnetic measurements, the (BEDT-TTF)(Me,TCNQ) and (BEDT-TTF)(ClMeTCNQ) complexes were neutral, while the (BEDO-TTF)(Cl(2)TCNQ), complex was found to be ionic. Among these complexes, anomalous magnetic properties were observed in the ionic complex of (BEDO-TTF)(Cl(2)TCNQ). (BEDO-TTF)(CI,TCNQ) is a magnetic insulator with Curie-Weiss behavior in magnetic susceptibility followed by a sharp drop at around 120 K, which is in sharp contrast to conventional "spin-Peierls-type'' nonmagnetic mixed-stack ionic compounds.

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We developed the uniaxial strain method to compress a crystalline sample along any direction without involving Poisson's effect. The uniaxial strain is realized by inserting a composite of either the sample embedded in epoxy or the sample in frozen oil into a cylinder much harder than the sample composite followed by the application of external forces to a piston put on the sample composite. We verified, by using a strain gauge embedded in the epoxy or the frozen oil, that the strain thus created has the uniaxial nature. Resistance measurements on two kinds of organic conductors, alpha-(BEDT-TTF)(2)KHg(SCN)(4) and alpha-(BEDT-TTF)(2)I-3 under the uniaxial strain showed novel electric properties that have never been found under hydrostatic pressures. Their properties were found to be largely dominated by the direction of the uniaxial strain even when it is applied along directions in the conducting plane having a two-dimensional nature. (C) 2000 American Institute of Physics. [S0034-6748(00)05001-2].

DOI： 10.1063/1.1150180

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We have studied the semiclassical and non-semiclassical behaviors of magnetoresistance (MR) in a quasi-one-dimensional (Q1D) conductor (TMTSF)2ClO4. Based on the Boltzmann equation, we numerically investigated possible semiclassical &#039;angular effects&#039;, the characteristic patterns of the field-orientation-dependence of MR, in the general Q1D conductors. Particularly, we have clarified the complicated situation around B//1D-axis in which different angular effects are mixed up. The angular dependent MR features in the metallic phase of (TMTSF)2ClO4almost obey the semiclassical theory except a dip structure around B//b&#039;. As for this non-semiclassical feature, we discuss the possibility of the one-body and many-body field-induced electron confinement onto a single conducting layer.

DOI： 10.1016/S0379-6779(98)00289-6

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

The title compounds show unique crystal structures involving double-column donor arrangements, affording characteristic fourfold Fermi surfaces. They show metallic conductivities, accompanied by metal-insulator transitions at low temperatures.

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

The BEDT-TTF based mixed-stack charge-transfer (CT) complexes have been investigated for a series of isostructural compounds. The ionic complex of (BEDO-TTF)(Cl(2)TCNQ) is a magnetic insulator with showing Curie-Weiss behavior in magnetic susceptibility, in sharp contrast to the conventional mixed-stack CT complexes. The (BEDT-TTF)(ClMeTCNQ) compound undergoes neutral-ionic (NI) phase transition at high pressure.

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

It was found that (BETS)(2)(Cl(2)TCNQ) is an all-organic superconductor, where BETS is bis(ethylenedithio)tetraselenafulvalene and Cl(2)TCNQ is 2,5-dichlorotetracyanoquinodimethane. The superconducting critical temperature was 1.3 K+/-0.3 K under pressure.

DOI： 10.1246/cl.1999.333

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DOI： 10.1016/S0038-1098(99)00113-1

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

The electrical resistivity and the magnetoresistance have been measured for icosahedral phases of Zn-Mg-RE (RE=Y, Gd). Electrical resistivities of bulk samples of Zn56Mg36Y8, annealed ribbon samples of Zn62Mg30Y8 and annealed ribbon samples of Zn55Mg35.5Gd9.5 are 1 m Ohm cm, 0.3 m Ohm cm and 0.3 m Ohm cm. respectively. The resistivities of all the samples decrease by 5 similar to 7% from 4.2 K to 273 K. At low temperatures, the conductivity of Zn-Mg-Y obeys T-1/2 dependence, while the resistivity of Zn-Mg-Gd obeys ln T dependence, where Gd atoms bear magnetic moments. In Zn-Mg-Y; the magnetoresistance is negative and insensitive to temperature, while in Zn-h Ig-Gd it is positive in a low field range and becomes negative at high field with its magnitude larger at lower temperature. These results are interpreted by the theories of electron-electron interaction, weak localization and s-d exchange interaction.

DOI： 10.1143/JPSJ.66.1097

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

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/cr0306539

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DOI： 10.1143/JPSJ.72.1152

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The roles of donor layers and acceptor stacks in the electronic properties of the charge transfer complex, (BETS)(2)(Br(2)TCNQ) were investigated by means of site-selective NMR measurements. Line broadening of Se-77 NMR indicating a magnetic ordering on the BETS site was observed at the metal-insulator transition temperature 12 K. This transition is caused by the spin-density-wave formation on the BETS layers. C-13 NMR on the cyano carbon in the Br(2)TCNQ molecule confirms that a spin singlet formation starts to develop on the one dimensional Br(2)TCNQ columns below 170 K and its three dimensional ordering appears below 80 K. From the analysis of the NMR line shape and shift, magnetic susceptibility was decomposed into the contributions of the BETS and Br(2)TCNQ sites.

DOI： 10.1103/PhysRevB.66.035104

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DOI： 10.1016/S1567-1739(02)00162-1

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Language：English   Publisher：ELSEVIER SCIENCE SA  

H-1, C-13 and Se-77 NMR measurements were performed to investigate the electronic properties of (BETS)(2)(X(2)TCNQ) (X=Cl, Br). The susceptibility was decomposed into the contributions of BETS and X(2)TCNQ site. The line broadening of the H-1/Se-77 NMR spectra were observed in the Br(2)TCNQ complex at the metal insulator transition temperature, 12 K. Non magnetic spin singlet formation on the Br2TCNC2 site was observed at 80 K by C-13 NMR. Line broadening of the H-1 NMR spectra were also observed in the Cl(2)TCNQ complex at the metal insulator transition temperature. The insulating state of the Br and Cl(2)TCNQ complexes under pressure are both magnetic. The holes on the BETS layers are relevant to the magnetic ordering.

DOI： 10.1016/S0379-6779(00)01048-1

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We found that (BETS)(2)(Cl(2)TCNQ) becomes superconducting under pressure, showing a maximum critical temperature of 1.3K at 3.5kbar. The superconductivity disappears at higher pressures and is replaced by an insulating phase. its isostructural complex with larger cell parameters, (BETS)(2)(Br(2)TCNQ), displays a metal-insulator transition at 13K under ambient pressure.

DOI： 10.1016/S0379-6779(00)00915-2

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We synthesized donor-acceptor charge-transfer complexes composed of BEDT-TSeF ( or "BETS") and. TCNQ derivatives and obtained isosturctual complexes represented as (BETS)(2)(X(1)X(2)TCNQ) (X-1,X-2=Cl, Br). The single crystals of (BETS)(2)(Cl(2)TCNQ) preserve the metallic state down to 2K.

DOI： 10.1016/S0379-6779(98)00492-5

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Language：English   Publisher：ELSEVIER SCIENCE SA  

Charge transfer complexes of bis(ethylenediselena)-tetrathiafulvalene.(BEDSe-TTF) with a variety of Fn-TCNQ (n = 1, 2, 4, including isomers) are synthesized. In this family, only F-1,-TCNQ afforded a conducting complex. Other accepters gave mixed stack insulators, which undergo antiferromagnetic phase transitions. 2,5-F-2- and 2,3-F-2-TCNQ also yielded a polymorph with a novel type of crystal structure, showing a double-chain donor arrangement.

DOI： 10.1016/S0379-6779(98)00578-5

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