研究者詳細 - 近藤　隆祐

論文 - 近藤　隆祐

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Hump like resistance anomaly in organic conductor β"-(BEDT-TTF)(2)CsCd(SCN)(4) 査読

Kondo Ryusuke, Otsuji Jun, Kagoshima Seiichi, Nogami Yoshio

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 6 ) 2008年6月

Charge ordered metal and pressure-induced superconductivity in the two-dimensional organic conductor beta-(DODHT)(2)PF(6) 査読

Akito Kobayashi, Yoshikazu Suzumura, Momoka Higa, Ryusuke Kondo, Seiichi Kagoshima, Hiroyuki Nishikawa

JOURNAL OF PHYSICS-CONDENSED MATTER 20 ( 12 ) 2008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：IOP PUBLISHING LTD

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

Development of uniaxial elongation method and its application to low dimensional conductors 査読

Hiroki Kowada, Ryusuke Kondo, Seiichi Kagoshima

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 11 ) 2007年11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

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

Structural studies of pressure-induced organic superconductor beta ''-(DODHT)(2)PF6 having charge-ordering phase at ambient pressure 査読

Momoka Higa, Ryusuke Kondo, Seiichi Kagoshima, Hiroyuki Nshikawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 3 ) 2007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：PHYSICAL SOC JAPAN

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

A possible internal deformation of the charge ordering and its meta-stability in the organic conductor theta-(BEDT-TTF)(2)CsZn(SCN)(4) 査読

Ryusuke Kondo, Mornoka Higa, Seiichi Kagoshima

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 3 ) 2007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：PHYSICAL SOC JAPAN

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

Anisotropic superconducting transition in beta ''-(DODHT)(2)PF6 査読

Momoka Higa, Ryusuke Kondo, Seiichi Kagoshima, Hiroyuki Nishikawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 186 - 187 2007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：PHYSICAL SOC JAPAN

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

Ultrahigh-pressure effects in metallo-organics 査読

Seiichi Kagoshima, Ryusuke Kondo, Nobuyuki Matsushita, Momoka Higa, Sergey V. Ovsyannikov, Nadezhda A. Shaydarova, Vladimir V. Shchennikov, Andrey Y. Manakov, Anna Y. Likhacheva

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 ( 1 ) 418 - 423 2007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：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

High-pressure research in organic conductors 査読

Keizo Murata, Seiichi Kagoshima, Syuma Yasuzuka, Harukazu Yoshino, Ryusuke Kondo

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 5 ) 2006年5月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

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

A one-dimensional coordination polymer, BBDTA center dot InCl4: Possible spin-Peierls transition with high critical temperature of 108 K 査読

Wataru Fujita, Kunio Awaga, Ryusuke Kondo, Seiichi Kagoshima

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 ( 18 ) 6016 - 6017 2006年5月

Electrical and Structural Properties of θ-type BEDT-TTF Organic Conductors under Uniaxial Strain 査読

R. Kondo, M. Higa, S. Kagoshima, H. Hoshino, T. Mori, H. Mori

Journal of the Physical Society of Japan 75 ( 4 ) 044716 2006年4月

Superconducting and charge ordering phases of two-dimensional organic conductors 査読

R. Kondo, M. Higa, S. Kagoshima

JOURNAL OF LOW TEMPERATURE PHYSICS 142 ( 3-4 ) 535 - 538 2006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：SPRINGER/PLENUM PUBLISHERS

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).

Magnetic correlation in BETS2(Cl(2)TCNQ) 査読

Y. Takano, K. Hiraki, T. Takahashi, R. Kondo, S. Kagoshima, T. Hasegawa, T. Mocihda, Y. Iwasa

JOURNAL OF LOW TEMPERATURE PHYSICS 142 ( 3-4 ) 647 - 650 2006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：SPRINGER/PLENUM PUBLISHERS

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

Ultra high pressure application to organic conductors 査読

S. Kagoshima, R. Kondo, N. Matsushita, S. V. Ovsyannikov, N. A. Shaidarova, V. V. Shchennikov

JOURNAL OF LOW TEMPERATURE PHYSICS 142 ( 3-4 ) 409 - 412 2006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：SPRINGER/PLENUM PUBLISHERS

Under pressures as high as 20 GPa at room temperature the electronic and structural properties of organic conductors were measured to search for interesting pressure regimes where novel electronic states were expected. Thermopower, two-probe electrical resistance and contraction of sample's volume were measured on the organic conductors: theta-(BEDT-TTF)(2)CsZn(SCN)(4), alpha-(BEDT-TTF)(2)I-3, (BEDT-TTF)(2)PF6 and (BEDT-TTF)-TCNQ. All the materials exhibited a positive thermopower of the order of 10 mu V/K. At about 4-7 GPa (crossover pressure P-x) sharp changes were found in the pressure dependence of electronic and mechanical properties of all the substances under consideration related probably to the structural changes under pressure.

DOI： 10.1007/s10909-006-9126-7

その他リンク： http://orcid.org/0000-0003-1022-430X

Charge ordered insulating state in DODHT salts 査読

H. Nishikawa, Y. Sato, T. Kodama, K. Kikuchi, I. Ikemoto, J. Yamada, H. Oshio, R. Kondo, S. Kagoshima

JOURNAL OF LOW TEMPERATURE PHYSICS 142 ( 3-4 ) 633 - 636 2006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：SPRINGER/PLENUM PUBLISHERS

Radical salts based on DODHT [(1,4-dioxane-2,3-diyldithio)dihydrotetra-thialulvalene] are semiconductors at ambient pressure, but some salts (PF6, AsF6, and BF4 center dot H2O salts) exhibit supuerconducting transition under hydrostatic pressure. X-ray diffraction and magnetic susceptibility measurements at ambient pressure for PF6 salt revealed that the insulating phase at ambient pressure corresponds to a charge ordering (CO) state with stripe-type charge pattern. While the similar magnetic behavior was observed for BF4 salt, temperature dependence of magnetic susceptibility of AsF6 salt is quite different from those of the other salts.

DOI： 10.1007/s10909-006-9106-y

Magneto-transport properties in the density wave phase of beta ''-(BEDT-TTF)(2)CsCd(SCN)(4) 査読

R. Kondo, J. Otsuji, S. Kagoshima

YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS 51 327 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

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

Structural and electronic properties of a new molecular conductor, alpha-(BEDT-TTF)(2)CsCd(SCN)(4) 査読

R Kondo, M Higa, S Kagoshima

SOLID STATE COMMUNICATIONS 137 ( 12 ) 637 - 640 2006年

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

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

Fermi surface study of organic conductors using a magnetooptical measurement under high magnetic fields 査読

M. Kimata, H. Ohta, K. Koyama, M. Motokawa, R. Kondo, S. Kagoshima, H. Tanaka, M. Tokumoto, H. Kobayashi, A. Kobayashi

YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS 51 359 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IOP PUBLISHING LTD

Magneto-optical measurements have been performed in organic conductors beta''-(BEDT-TTF)(2)CsCd(SCN), and lambda-(BETS)(2)FeCl4. Although the zero magnetic field ground state of beta"-(BEDT-TTF)(2)CsCd(SCN)(4) is considered as the density wave state, periodic orbit resonances (POR's) attributed to quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces (FS's) have been observed above 6 T. The existence of these FS's are predicted by the band calculation based on room temperature lattice parameters. This result may suggest the destruction of the density wave state at 6 T, and the primal metallic state revives in the high field phase above 6 T. In the case of lambda-(BETS)(2)FeCl4, large changes of the transmission intensity of electromagnetic waves around 10 T, which correspond to the insulator-metal transition, have been observed. However, no POR-like resonance has been observed. This may be due to the restriction of the observed frequency-field region.

DOI： 10.1088/1742-6596/51/1/084

Crystal structure analysis under uniaxial strain at low temperature using a unique design of four-axis x-ray diffractometer with a fixed sample 査読

R Kondo, S Kagoshima, J Harada

REVIEW OF SCIENTIFIC INSTRUMENTS 76 ( 9 ) 093902 2005年9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 INST PHYSICS

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

Charge ordering and pressure-induced superconductivity in "-(DODHT)2PF6. 査読

H. Nishikawa, Y. Sato, T. Kodama, K. Kikuchi, I. Ikemoto, J. Yamada, H. Oshio, R. Kondo, S. Kagoshima

Phys. Rev. B 72 ( 5 ) 052510 2005年8月

Molecular arrangement and electronic band structure of theta-(BEDT-TTF)(2)CsZn(SCN)(4) controlled by uniaxial compression 査読

R Kondo, M Higa, S Kagoshima, H Hoshino, T Mori, H Mori

CURRENT APPLIED PHYSICS 4 ( 5 ) 484 - 487 2004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：ELSEVIER SCIENCE BV

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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