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X-ray Absorption Spectra in Pyrochlore Niobates 査読

S. Torigoe, Y. Ishimoto, N. Hanasaki, Y. Nogami, D. Matsumura, K. Yoshii, Y. Yoneda, Y. Nishihata

INTERNATIONAL CONFERENCE ON FRUSTRATION IN CONDENSED MATTER (ICFCM) 320 2011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

The X-ray absorption spectra reveal that the valence of the Nb ion, and the displacement of the Nb ions from the center of the oxygen octahedra in the pyrochlore niobates YCaNb(2)O(7) and NdCaNb(2)O(7), which is consistent with the previous report of the neutron diffraction.

DOI： 10.1088/1742-6596/320/1/012078

Hydrothermal Synthesis of Hexagonal Vanadium Oxide 査読

T. Tokuyama, T. Okusako, K. Mikami, N. Hanasaki, Y. Nogami

INTERNATIONAL CONFERENCE ON FRUSTRATION IN CONDENSED MATTER (ICFCM) 320 2011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

We synthesize the hexagonal vanadium oxide containing the alkaline-metal ion (Li, Na, and K). The crystal belongs to the magnetoplumbite-type structure. The title compound, in which the vanadium valance is not an integer, shows the metallic and the paramagnetic behavior. The electronic specific heat coefficient gamma is 34.7 mJ/K(2)mol, which is perhaps due to the spin fluctuation.

DOI： 10.1088/1742-6596/320/1/012073

Field-Induced Successive Phase Transitions in the Charge Density Wave Organic Conductor HMTSF-TCNQ 査読

Keizo Murata, Keiichi Yokogawa, Kensuke Kobayashi, Kosuke Masuda, Takahiko Sasaki, Yuki Seno, Natarajan Rani Tamilselvan, Harukazu Yoshino, James S. Brooks, Denis Jerome, Klaus Bechgaard, Mikio Uruichi, Kyuya Yakushi, Yoshio Nogami, Reizo Kato

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 10 ) 2010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

The magnetoresistance of quasi-1D two-chain organic conductor HMTSF-TCNQ (hexamethylenetetraselenafulvalene-tetracyanoquinodimethane), which shows charge density wave transition at ambient pressure, was studied under pressure up to 27 T and 31 T, in two high field facilities. We found a kink structure in the magnetoresistance reminiscent of field-induced spin density wave at an intermediate pressure of 1.5 GPa between 0 and 2 GPa. We speculate that these are successive quantum phases induced by magnetic field.

DOI： 10.1143/JPSJ.79.103702

Relaxation of geometrical frustration in NbSe3 topological crystals 査読

T. Tsuneta, K. Yamamoto, N. Ikeda, Y. Nogami, T. Matsuura, S. Tanda

PHYSICAL REVIEW B 82 ( 1 ) 2010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：AMER PHYSICAL SOC

Here we report the structural study of NbSe3 topological crystals via synchrotron x-ray measurements on individual microcrystals. Topological crystals are characterized by the shape of a ring or a twisted loop, thereby representing a translational and orientational order confined in topologically nontrivial, curved geometries. The crystal lattice of topological crystals is under considerable amount of strain. The volume-averaged strain asymptotically increases with thickness and curvature of a crystal. We present a structural model in which a ring crystal is composed of well-ordered domains in the shape of concentric cylinders. The internal structure reflects periodic accumulation and release of strain during the growth.

DOI： 10.1103/PhysRevB.82.014105

Pressure effect on the competing charge ordered states in theta-(BEDT-TTF)(2)CsZn(SCN)(4) 査読

M. Watanabe, M. Osanai, Y. Dohi, Y. Ishikawa, Y. Noda, Y. Nogami, I. Terasaki, H. Mori, T. Mori

PHYSICA B-CONDENSED MATTER 405 ( 11 ) S229 - S231 2010年6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

The pressure effect on the competing charge ordered states in theta-(BEDT-TTF)(2)CsZn(SCN)(4) was investigated by X-ray diffraction method Under 1 1 GPa the threefold long range ordered superstructure with the wave vector q(1) = (-2/3 0 1/3) was detected below 240 K and the twofold charge ordering with the wave vector q(2) = (0 0 1/2) was suppressed from 3 to 300 K by the pressure (C) 2010 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2010.03.018

Nonequilibrium charge ordering in theta-(BEDT-TTF)(2)MM '(SCN)(4) (M=Rb, Cs; M '=Co, Zn) 査読

Ichiro Terasaki, Shuichi Tasaki, Shigeru Ajisaka, Yoshio Nogami, Noriaki Hanasaki, Masashi Watanabe, Hatsumi Mori, Takehiko Mori

PHYSICA B-CONDENSED MATTER 405 ( 11 ) S217 - S220 2010年6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

Giant nonlinear conduction in the charge ordered organic conductor theta-(BEDT-TTF)(2)MM'(SCN)(4) (M = Cs Rb M' = Co Zn) is analyzed in relation to the current-induced suppression of the charge ordered state characterized by a wave vector of q(2) = (0k 1/2) On the basis of a theory of the nonequilibrium Peierls transition the energy gap is calculated as a function of current density J(ext) which is found to depend weakly on temperature in an intermediate temperature range This justifies the evaluation of the found to be consistent with the calculation We compare the present results with nonequilibrium and Ail i IS charge-order energy gap Delta from the nonlinear resistivity rho assuming rho proportional to exp[Delta(J(ext))/k(B)T] and Delta(J(ext)) superconducting states induced by excess quasiparticles and discuss a mechanism of current-Induced suppression of the charge ordering in the title compound (C) 2009 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2009.11.073

Charge Order Competition Leading to Nonlinearity in Organic Thyristor Family 査読

Yoshio Nogami, Noriaki Hanasaki, Masashi Watanabe, Kenichiro Yamamoto, Takayoshi Ito, Naoshi Ikeda, Hiroyuki Ohsumi, Hidenori Toyokawa, Yukio Noda, Ichiro Terasaki, Hatsumi Mori, Takehiko Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 ( 4 ) 2010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：PHYSICAL SOC JAPAN

Simultaneous synchrotron radiation and transport measurements for the organic thyristor family compound theta-(BEDT-TTF)(2)RbZn(SCN)(4) have revealed the presence of microscopic competing domains between the twofold and 3 x 4 charge orderings in a triangular lattice. In contrast to conventional correlated electron systems, charge ordering is a unique critical parameter of phase competition. With external current, only the twofold ordering melts, which is responsible for the emergence of a nonlinear response.

DOI： 10.1143/JPSJ.79.044606

Interplay of charge-density waves and superconductivity in the organic conductor beta ''-(BEDT-TTF)(2)AuBr2 査読

Ryusuke Kondo, Momoka Higa, Seiichi Kagoshima, Noriaki Hanasaki, Yoshio Nogami, Hiroyuki Nishikawa

PHYSICAL REVIEW B 81 ( 2 ) 2010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：AMER PHYSICAL SOC

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

Commensurate-incommensurate urate transition of charge density waves in o-TaS3 査読

K. Inagaki, M. Tsubota, K. Ichimura, S. Tanda, K. Yamamoto, N. Hanasaki, Y. Nogami, N. Ikeda, T. Ito, H. Toyokawa

PHYSICA B-CONDENSED MATTER 404 ( 3-4 ) 396 - 398 2009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 BV

We report a synchrotron X-ray study of charge density waves (CDWs) in an o-TaS3 crystal. CDW of o-TaS3 has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. However, the details of the commensurate-incommensurate transition remain open problems, the example being whether the discommensuration exists or not in the neighborhood of the transition. We exploited the beamline BL02B1 of SPring-8. A two-dimensional detector was placed at a distance of 1300mm from the sample, providing an angle resolution of 0.0076 degrees. Temperature dependence of the Bragg peak (0 0 2) and satellite peak (1 - 12) + q was measured from 7 to 180 K. We found that a new phase in the temperature range of 130-50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. Below 50K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we suggested the dislocation configuration from the intensity of the two CDWs. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2008.11.017

Current-Density Dependence of the Charge-Ordering Gap in the Organic Salt theta-(BEDT-TTF)(2)CsM(SCN)(4) (M = Zn, Co, and Co0.7Zn0.3) 査読

Fumiaki Sawano, Tomohiro Suko, Taichi S. Inada, Shuichi Tasaki, Ichiro Terasaki, Hatsumi Mori, Takehiko Mori, Yoshio Nogami, Naoshi Ikeda, Masashi Watanabe, Yukio Noda

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 ( 2 ) 2009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：PHYSICAL SOC JAPAN

We have measured and analyzed the resistivity and voltage-current characteristics of the charge-ordered organic salt theta-(BEDT-TTF)(2)CsM(SCN)(4) (M = Zn, Co, and Co(0.7)Z(0.3)). At 4.3 K, all the samples show giant nonlinear conduction, in which the c-axis resistivity markedly decreases with external current by a factor of 10 against a small electric field of 1 V/cm. The temperature dependence of the resistivity is well described by an activation law, the activation energy of which is evaluated to be 2 meV in the low-current limit, and linearly decreases with external current. The activation energy and x-ray intensity near q(2) = (0, k, 1/2) are found to show the same dependence on current density. This coincidence strongly suggests that the energy gap of the charge order indexed by q(2) is an order parameter of this phenomenon.

DOI： 10.1143/JPSJ.78.024714

Synchrotron X-ray study of charge density waves in o-TaS3 査読

K. Inagaki, M. Tsubota, K. Ichimura, S. Tanda, K. Yamamoto, N. Hanasaki, Y. Nogami, N. Ikeda, T. Ito, H. Toyokawa

25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4 150 2009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

We report a synchrotron X-ray study of charge density waves (CDW) in an o-TaS3 crystal. CDW of o-TaS3 has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. We exploited the beamline BL02B1 of SPring-8. Temperature dependence of the Bragg peak (002) and satellite peak (1 -1 2)+(q) over right arrow was measured from 7 K to 180 K. We found that a new phase in a temperature range of 130-50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c)=0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. At 50 K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we determined the dislocation configuration from the intensity of the two CDWs.

DOI： 10.1088/1742-6596/150/4/042068

Temperature and electric-current dependence of charge-ordered domains in theta-(BEDT-TTF)(2)CsZn(SCN)(4) 査読

T. Ito, M. Watanabe, K. -I. Yamamoto, N. Ikeda, Y. Nogami, Y. Noda, H. Mori, T. Mori, I. Terasaki

EPL 84 ( 2 ) 2008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：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY

We report X-ray diffraction measurements of the charge-ordered organic conductor theta-(BEDT-TTF)(2)CsZn(SCN)(4) at various temperatures with external currents. The two kinds of diffuse scattering observed at q(1) = (2/3 k 1/3) and q(2) = (0 k 1/2) exhibit remarkable difference in the interplane correlation along the b-axis, the temperature dependence, and the electric-current dependence. These observations suggest that the two diffuse scatterings come from spatially different charge-ordered domains. The external current melts the q(2)-type domains, which can control the competition of the two orders. Copyright (C) EPLA, 2008

DOI： 10.1209/0295-5075/84/26002

Field-induced discommensuration in charge density waves in o-TaS3 査読

Katsuhiko Inagaki, Masakatsu Tsubota, Kazuki Higashiyama, Koichi Ichimura, Satoshi Tanda, Kenichiro Yamamoto, Noriaki Hanasaki, Naoshi Ikeda, Yoshio Nogami, Takayoshi Ito, Hidenori Toyokawa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 9 ) 2008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：PHYSICAL SOC JAPAN

We report a synchrotron X-ray Study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist ill the temperature range of 130-50K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric Current dependence of the intensity of the two CDWs. The result implies Cor the first time that discommensurations are induced ill the commensurate CDW by applying an electric field.

DOI： 10.1143/JPSJ.77.093708

Hump Like Resistance Anomaly in Organic Conductor β"-(BEDT-TTF)_2CsCd(SCN)_4

Kondo Ryusuke, Otsuji Jun, Kagoshima Seiichi, NOGAMI Yoshio

Journal of the Physical Society of Japan 77 ( 6 ) "63702 - 1"-"63702-4" 2008年6月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

We investigate the low-temperature electronic phase of a two-dimensional organic conductor, β"-(BEDT-TTF)_2CsCd(SCN)_4 [where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene], which has a large hump between 32 and around 5K 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 32K, although the rule is valid above 32K, and II) weak superlattice spots appear at 15.6K 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 32K 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.

Non-thermal evidence for current-induced melting of charge order in theta-(BEDT-TTF)(2)CsZn(SCN)(4) 査読

Masashi Watanabe, Kenichiro Yamamoto, Takayoshi Ito, Yusaku Nakashima, Makoto Tanabe, Noriaki Hanasaki, Naoshi Ikeda, Yoshio Nogami, Hiroyuki Ohsumi, Hidenori Toyokawa, Yukio Noda, Ichiro Terasaki, Fumiaki Sawano, Tomohiro Suko, Hatsumi Mori, Takehiko Mori

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

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

Ryusuke Kondo, Jun Otsuji, Seiichi Kagoshima, Yoshio Nogami

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

Relaxation of geometrical frustration in NbSe3 topological crystals 査読

Tsuneta Taku, Nogami Yoshio, Yamamoto Kenichirou, Ikeda Naoshi, Tanda Satoshi

ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 64 C509 - C509 2008年

Spin-Peierls transition in the charge-ordered organic conductor theta-BEDT-TTF2RbZn(SCN)(4) 査読

Masashi Watanabe, Yukio Noda, Yoshio Nogami, Hatsumi Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 ( 12 ) 2007年12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

X-ray investigation of theta-BEDT-TTF2RbZn(SCN)4 was carried out around the temperature of the phase transition to the nonmagnetic state. theta-BEDT-TTF2RbZn(SCN)4 exhibits a metal-insulator transition accompanied by a charge ordering at T-CO = 200 K. In the one-dimensional spin chain formed by this charge ordering, BEDT-TTF donor molecules are aligned uniformly along the a-axis obeying the 2(1) screw symmetry of the space group P2(1)2(1)2(1) below Tco. At the ground state, the system becomes nonmagnetic. The transition temperature T-c to the nonmagnetic phase seems to scatter around 20 K and may depend on the sample. We found that the extinction rule of [h00: It = 2n] no longer applied below approximately 20 K. This indicated a symmetry breaking of the 2(1) screw symmetry along the a-axis in the nonmagnetic state. The observed peak intensities violating the extinction rule were about 10(-4) of other general Bragg reflection. peak intensities. This structural change should be interpreted as a spin-Peierls transition in the charge-ordered system. In addition, a corresponding anomaly was observed in the lattice parameter a.

DOI： 10.1143/JPSJ.76.124602

Charge ordering in organic conductors 査読

Toshihiro Takahashi, Yoshio Nogami, Kyuya Yakushi

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

Present status of experiments on charge ordering (CO) phenomena observed in organic molecular conductors is reviewed. Experimental techniques to detect and analyze the CO, i.e., NMR, X-ray and Infrared/Raman spectroscopy, are described and the experimental results in typical materials exhibiting CO are summarized. (DI-DCNQI)(2)Ag, (TMTTF)(2)X, alpha-(BEDT-TTF)(2)I-3, theta-(BEDT-TTF)(2)RbZn(SCN)(4) and related materials are discussed. Charge disproportionation without long-range order observed in numbers of materials are also included.

DOI： 10.1143/JPSJ.75.051008

Is the two dimensional organic Conductor, iota-(EDO-S,S-DMEDT-TTF)(2)(AuCl2)(1+y) clean or dirty? 査読

T. Nakanishi, S. Yasuzuka, M. Teramura, L. Li, T. Fujimoto, T. Sasaki, T. Konoike, T. Terashima, S. Uji, Y. Nogami, G. C. Anyfantis, G. C. Papavassiliou, Keizo Murata

JOURNAL OF LOW TEMPERATURE PHYSICS 142 ( 3-4 ) 247 - 252 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

The transport properties of organic tau-type conductors seem to be very clean as well as very dirty depending on what we observe. To clarify this problem, we studied temperature and magnetic field dependence of resistivity, rho(T, B), in tau-(EDO-S,S-DMEDT-TTF)(2)(AuCl2)(1+y). The properties that favor "probably dirty" are: i) stepwise rho(a)(T) increase below 20 K, which is suppressed by magnetic field, and ii) contrasted difference in rho(T) as well as magnetization M(T) between field cooled (FC) and zero field cooled (ZFC). On the other hand, Shubnikov de Haas oscillations with very low Dingle temperature (T-D = 1.5 K) are typical of clean system. Based on these observations, we conclude this system changes from "dirty" to "clean" system by increase of magnetic field.

DOI： 10.1007/s10909-006-9195-7

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