研究者詳細 - 近藤　隆祐

論文 - 近藤　隆祐

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Phase transition on (BEDO-TTF) (Cl(2)TCNQ): Spin dynamics observed by NMR measurements 査読

M Takahashi, K Hiraki, T Takahashi, T Hasegawa, R Kondo, S Kagoshima

JOURNAL DE PHYSIQUE IV 114 141 - 142 2004年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：E D P SCIENCES

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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Crystal and electronic structures of alpha-(BEDT-TTF)(2)I-3 under uniaxial strains 査読

R Kondo, S Kagoshima

JOURNAL DE PHYSIQUE IV 114 523 - 525 2004年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：E D P SCIENCES

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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2k(F) transitions in a series of (DMET)(2)(X(1)X(2)TCNQ) (X(1), X(2)=Br, Cl, F, CH(3), H): Subsidiary lattice effect by anion radicals 査読

T Sato, T Hasegawa, T Akutagawa, T Nakamura, R Kondo

PHYSICAL REVIEW B 69 ( 7 ) 2004年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Structural and magnetic properties were investigated in a series of isomorphous 2:1 donor-acceptor-type organic charge-transfer (CT) complexes of (DMET)(2)(X(1)X(2)TCNQ) [DMET denotes dimethyl(ethylenedithio)diselenadithiafulvalene, TCNQ denotes tetracyanoquinodimethane, X(1),X(2)=Br,Cl,F,CH(3),H]. In these complexes, donors (D's) formed quasi-one-dimensional (Q1D) molecular stacks (D=+1/2), which were bridged with each other, by acceptor molecules whose molecular planes were parallel to the stacking axes. By the magnetic measurements, we found that the compounds could be classified into two groups in terms of the 2k(F) transitions of the donor stacks: two complexes exhibited the transitions at around room temperature, while the other two at lower temperature below 10 K. We discuss the origin of the difference in the observed 2k(F) transitions in terms of the subsidiary lattice effect by the acceptor molecules on the Q1D donor stacks.

DOI： 10.1103/PhysRevB.69.075103

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2kF transitions in a series of (DMET)2(X 1X2TCNQ) (X1, X2=Br, Cl, F, CH 3, H): Subsidiary lattice effect by anion radicals

T. Sato, T. Hasegawa, T. Akutagawa, T. Nakamura, R. Kondo

Physical Review B - Condensed Matter and Materials Physics 69 ( 7 ) 751031 - 751035 2004年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Structural and magnetic properties were investigated in a series of isomorphous 2:1 donor-acceptor-type organic charge-transfer (CT) complexes of (DMET)2(X1X2TCNQ) [DMET denotes dimethyl(ethylenedithio)diselenadithiafulvalene, TCNQ denotes tetracyanoquinodimethane, X1, X2=Br, Cl,F,CH 3,H]. In these complexes, donors (D's) formed quasi-one-dimensional (Q1D) molecular stacks (D = + 1/2), which were bridged with each other, by acceptor molecules whose molecular planes were parallel to the stacking axes. By the magnetic measurements, we found that the compounds could be classified into two groups in terms of the 2kF transitions of the donor stacks: two complexes exhibited the transitions at around room temperature, while the other two at lower temperature below 10 K. We discuss the origin of the difference in the observed 2kF transitions in terms of the subsidiary lattice effect by the acceptor molecules on the Q1D donor stacks.

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Crystal structure and electronic band structure of the organic superconductor alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) under uniaxial strain 査読

R Kondo, S Kagoshima, M Maesato

PHYSICAL REVIEW B 67 ( 13 ) 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

In order to investigate the relationship between the crystal structure and electronic properties, crystal structure analysis of the organic superconductor alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4), where BEDT-TTF is the abbreviation of bis(ethylenedithio)tetrathiafulvalene, was performed under uniaxial compressive strain along each crystal axis. It was found that (i) almost ideal uniaxial strain was realized, that is, the unit cell was compressed only along the direction parallel to the external force; (ii) the calculated Fermi surface in the two-dimensional conducting layer was reduced along the k(c) axis and expanded along the k(a) axis under b(')- and c-axial strains, but vice versa under a-axial strain; and (iii) changes in the density of states at the Fermi level [DOS(E-F)] calculated from the obtained structures were qualitatively consistent with the observed change of the superconducting transition temperature.

DOI： 10.1103/PhysRevB.67.134519

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Crystal structure and electronic band structure of the organic superconductor α-(BEDT-TTF)2NH4HG(SCN)4 under uniaxial strain 査読

Ryusuke Kondo, Seiichi Kagoshima, Mitsuhiko Maesato

Physical Review B - Condensed Matter and Materials Physics 67 ( 13 ) 1345191 - 1345196 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

In order to investigate the relationship between the crystal structure and electronic properties, crystal structure analysis of the organic superconductor α-(BEDT-TTF)2NH4Hg(SCN)4, where BEDT-TTF is the abbreviation of bis (ethylenedithio)tetrathiafulvalene, was performed under uniaxial compressive strain along each crystal axis. It was found that (i) almost ideal uniaxial strain was realized, that is, the unit cell was compressed only along the direction parallel to the external force
(ii) the calculated Fermi surface in the two-dimensional conducting layer was reduced along the kc axis and expanded along the ka axis under b'- and c-axial strains, but vice versa under a-axial strain
and (iii) changes in the density of states at the Fermi level [DOS(EF)] calculated from the obtained structures were qualitatively consistent with the observed change of the superconducting transition temperature.

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Band structure control of organic superconductors by the uniaxial strain method 査読

S. Kagoshima, R. Kondo, M. Maesato

Synthetic Metals 137 ( 1-3 ) 1163 - 1165 2003年

Uniaxial strain study of electronic and crystal structures of organic conductors 査読

S. Kagoshima, R. Kondo, M. Chusho, M. Maesato, T. Mori, H. Mori, S. Tanaka

Synthetic Metals 133-134 145 - 146 2003年

Crystal and band structures of organic superconductor under the uniaxial strain 査読

R. Kondo, S. Kagoshima, M. Maesato

Physica C: Superconductivity and its Applications 388-389 601 - 602 2003年

Crystal structure of organic superconductor, α-(BEDT-TTF)₂NH₄Hg(SCN)₄, under the uniaxial strain 査読

R. Kondo, S. Kagoshima, M. Maesato

Synthetic Metals 133-134 137 - 139 2003年

Metal-insulator transition of donor-acceptor-type organic charge-transfer complex (BETS)2(Br2TCNQ): Site-selective NMR measurements 査読

K. Hiraki, S. Furuta, T. Takahashi, R. Kondo, S. Kagoshima, T. Hasegawa, T. Mochida, Y. Iwasa

Physical Review B - Condensed Matter and Materials Physics 66 ( 3 ) 351041 - 351046 2002年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

The roles of donor layers and acceptor stacks in the electronic properties of the charge transfer complex, (BETS)2(Br2TCNQ) were investigated by means of site-selective NMR measurements. Line broadening of 77Se 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. 13C NMR on the cyano carbon in the Br2TCNQ molecule confirms that a spin singlet formation starts to develop on the one dimensional Br2TCNQ 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 Br2TCNQ sites.

DOI： 10.1103/PhysRevB.66.035104

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Metal-insulator transition of donor-acceptor-type organic charge-transfer complex (BETS)(2)(Br(2)TCNQ): Site-selective NMR measurements 査読

K Hiraki, S Furuta, T Takahashi, R Kondo, S Kagoshima, T Hasegawa, T Mochida, Y Iwasa

PHYSICAL REVIEW B 66 ( 3 ) 035104-1-035104-6 2002年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

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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Control of electronic properties of organic superconductors by uniaxial strain method 査読

S. Kagoshima, R. Kondo, T. Shibata, H. Hirai, M. Maesato, H. Hoshino, T. Mori, H. Mori, S. Tanaka

Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 380 77 - 84 2002年

Effects of uniaxial strain on α-(BEDT-TTF)₂MHg(SCN) ₄ [M=K, NH₄] 査読

M. Maesato, S. Kagoshima, R. Kondo, T. Shibata, H. Hirai

Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 376 195 - 200 2002年

Superconductivity and metal-insulator transition in twin-columnar organic superconductor, (BETS)(2)(X(2)TCNQ) [X=Cl, Br] 査読

R Kondo, T Hasegawa, T Mochida, S Kagoshima, Y Iwasa, K Hiraki, T Takahashi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 ( 10 ) 3023 - 3030 2001年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

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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Control of electronic properties of alpha-(BEDT-TTF)(2)MHg(SCN)(4) (M=K,NH4) by the uniaxial strain method 査読

M Maesato, Y Kaga, R Kondo, S Kagoshima

PHYSICAL REVIEW B 64 ( 15 ) 2001年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Systematic uniaxial strain studies of alpha-(BEDT-TTF)(2)MHg(SCN)(4) (M=K,NH4) 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 NH4 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 c/a, the ratio of the in-plane lattice parameters.

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Neutral-ionic phase transition of (BEDT-TTF)(ClMeTCNQ) under pressure 査読

T Hasegawa, T Akutagawa, T Nakamura, T Mochida, R Kondo, S Kagoshima, Y Iwasa

PHYSICAL REVIEW B 64 ( 8 ) 2001年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

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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Electronic properties of novel donor-acceptor type charge transfer complexes, (BETS)(2)(X(2)TCNQ) (X = Cl, Br): H-1, Se-77 and C-13-NMR 査読

K Hiraki, T Takahashi, R Kondo, S Kagoshima, T Hasegawa, T Mochida, Y Iwasa

SYNTHETIC METALS 120 ( 1-3 ) 917 - 918 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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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Metal-insulator transition in donor-acceptor type superconductor, (BETS)(2)(X(2)TCNQ) 査読

R Kondo, T Hasegawa, S Kagoshima, T Mochida, Y Iwasa

SYNTHETIC METALS 120 ( 1-3 ) 995 - 996 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

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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Electronic states of novel donor/acceptor type of organic superconductor, (BETS)(2)(Cl(2)TCNQ) 査読

K Hiraki, T Takahashi, R Kondo, S Kagoshima, T Hasegawa, T Mochida, Y Iwasa

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 62 ( 1-2 ) 401 - 403 2001年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

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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