研究者詳細 - 野上　由夫

論文 - 野上　由夫

分割表示 130 件中 41 - 60 件目／全件表示 >>

X-ray and neutron transparent pulse magnets 査読

E. Ohmichi, N. Ikeda, Y. Nogami, T. Osada

YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS 51 498 - + 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

A new type of pulse magnet, x-ray and neutron transparent pulse magnet, is suggested for use in high-field diffraction experiments. The magnet is made of aluminum-based material, so we expect that the scattered beam penetrates the magnet body and hence the total number of reflection points available substantially increases. This feature possibly allows full determination of the lattice and magnetic structure in strong magnetic fields. To realize this idea, we constructed a prototype transparent magnet consisting of aluminum wire and duralumin reinforcement. With a portable capacitor bank, the maximum field of 25 T was successfully generated in a 1.6 mm bore, even though the aluminum wire is less strong and less conducting than copper wire. Since the total energy is small (E-bank similar to 100 J), high repetition rate, which is necessary for sufficient signal-to-noise ratio, is realized. Technical details, coil performance, and future prospects will be described.

DOI： 10.1088/174-6596/51/1/113

クリスタリット

坂田修身, 乾雅祝, 大高理, 木原國昭, 大嶋建一, 石沢伸夫, 八島正知, 川路均, 道上勇一, 野上由夫, 福永俊晴

日本結晶学会誌 48 ( 1 ) 92 - 96 2006年

X-ray structural study of charge and anion orderings of TMTTF salts 査読

Y Nogami, T Ito, K Yamamoto, N Irie, S Horita, T Kambe, N Nagao, K Oshima, N Ikeda, T Nakamura

JOURNAL DE PHYSIQUE IV 131 39 - 42 2005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：EDP SCIENCES S A

High resolution X-ray structure analyses and electronic structure calculation revealed the condition for the charge ordering(CO) observed in the (TMTTF)(2)X (Fabre) salts. The phase diagram of the electronic states including 2k(F) and 4k(F) CO has been proposed associated with magnitudes Of Molecular dimerization and tetramerization.

DOI： 10.1051/jp4:2005131008

Evidence of band-filling control of tau-type organic conductors by thermal treatment 査読

H Yoshino, T Nakanishi, L Li, K Murata, D Graf, ES Choi, JS Brooks, Y Nogami, GC Papavassiliou

SYNTHETIC METALS 153 ( 1-3 ) 453 - 456 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：ELSEVIER SCIENCE SA

The two dimensional (2D) organic conductor tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+y), (y <= 0.875) is known to exhibit sample dependence of the electric resistivity. The present authors assumed that the possible difference in y is responsible for the sample dependence and the amount of y can be effectively controlled for each crystal by thermal treatment. If it is the case,the band filling of the present compound can be also controlled. To observe the change in the band filling directly, the magnetoresistance was measured up to 45 T at 0.5 K for the magnetic field perpendicular to the conducting ab plane of the samples from one single crystal, one of which had been heated up to 400 K. Both the samples showed the two series of Shubnikov-de Haas oscillations of the magnetoresistance as reported previously. We, however, found the remarkable difference in the frequency of the slower oscillations between the virgin and heated samples. The X-ray study revealed that the thermal treatment does not affect the crystal structure related to the 2D band structure. Thus the frequency change by the thermal treatment is caused by the change in the band filling and it is tuned by heating the crystal.

DOI： 10.1016/j.synthmet.2005.07.329

An organic thyristor 査読

F Sawano, Terasaki, I, H Mori, T Mori, M Watanabe, N Ikeda, Y Nogami, Y Noda

NATURE 437 ( 7058 ) 522 - 524 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：NATURE PUBLISHING GROUP

Thyristors are a class of nonlinear electronic device that exhibit bistable resistance - that is, they can be switched between two different conductance states(1). Thyristors are widely used as inverters ( direct to alternating current converters) and for the smooth control of power in a variety of applications such as motors and refrigerators. Materials and structures that exhibit nonlinear resistance of this sort are not only useful for practical applications: they also provide systems for exploring fundamental aspects of solid- state and statistical physics. Here we report the discovery of a giant nonlinear resistance effect in the conducting organic salt(2) theta- ( BEDT- TTF) 2CsCo( SCN)(4), the voltage- current characteristics of which are essentially the same as those of a conventional thyristor. This intrinsic organic thyristor works as an inverter, generating an alternating current when a static direct- current voltage is applied. Whereas conventional thyristors consist of a series of diodes ( their nonlinearity comes from interface effects at the p- n junctions), the present salt exhibits giant nonlinear resistance as a bulk phenomenon. We attribute the origin of this effect to the current-induced melting of insulating charge- order domains, an intrinsically non- equilibrium phenomenon in the sense that ordered domains are melted by a steady flow.

DOI： 10.1038/nature04087

Determination of Band-filling Change in the Two-dimensional Organic Conductor, τ-(EDO-S, S-DMEDT-TTF)_2(AuBr_2)_<1+y>, (y≦0.875) by the Quantum Oscillation of Magnetoresistance

Yoshino Harukazu, Murata Keizo, Nakanishi Tsutomu, LI Lin, CHOI Eun Sang, GRAF David, BROOKS James S, NOGAMI Yoshio, PAPAVASSILIOU George C

Journal of the Physical Society of Japan 74 ( 1 ) 417 - 424 2005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：一般社団法人日本物理学会

The effect of thermal treatment on the transport properties is studied for a two-dimensional organic conductor τ-(EDO-S, S-DMEDT-TTF)_2(AuBr_2)_<1+y>, (y&le;0.875). The temperature dependence of the electric resistivity below room temperature was found to be changed from metallic down to low temperature to semiconducting by heating up to 420K. One of the two frequencies of Shubnikovde Haas oscillations are found to be different between the non-heated and heated parts from a single crystal, while no evidence of structural change in X-ray photograph was observed. The present result clearly shows that nominal valence or band filling can be controlled by simple thermal treatment for the quasi-two-dimensional organic metal. The mechanism of the change in the band filling is discussed in terms of anion decomposition.

DOI： 10.1143/JPSJ.74.417

Determination of band-filling change in the two-dimensional organic conductor, tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+y), (y <= 0.875) by the quantum oscillation of magnetoresistance 査読

H Yoshino, K Murata, T Nakanishi, L Li, ES Choi, D Graf, JS Brooks, Y Nogami, GC Papavassiliou

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 1 ) 417 - 424 2005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

The effect of thermal treatment on the transport properties is studied for a two-dimensional organic conductor tau-(EDO-S,S-DMEDT-TTF)(2)(AuBr2)(1+y), (y less than or equal to 0.875). The temperature dependence of the electric resistivity below room temperature was found to be changed from metallic down to low temperature to semiconducting by heating up to 420K. One of the two frequencies of Shubnikovde Haas oscillations are found to be different between the non-heated and heated parts from a single crystal, while no evidence of structural change in X-ray photograph was observed. The present result clearly shows that nominal valence or band filling can be controlled by simple thermal treatment for the quasi-two-dimensional organic metal. The mechanism of the change in the band filling is discussed in terms of anion decomposition.

DOI： 10.1143/JPSJ.74.417

Structural phase transition in two-dimensional kagome antiferromagnet m-N-methylpyridinium alpha-nitronyl nitroxide center dot BF4 center dot 1/3(Acetone) 査読

T Kambe, Y Nogami, K Oshima, W Fujita, K Awaga

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 4 ) 796 - 799 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：PHYSICAL SOC JAPAN

We found for the first time a structural phase transition in two-dimensional kagome antiferromagnet m-N-methylpyridinium alpha-nitronyl nitroxide (m-MPYNN)(.)BF(4)(.)1/3 (acetone). As, below T-s = 128.7 K, the intense satellite reflections are clearly observed at the modulation wave vector of q(s) = (1/3, 1/3, 0), the unit cell of the low-temperature phase is enlarged to root3a x root3a x c. In the low-temperature phase, the space group is determined to be P31c. The orientation of acetone molecules orders below T-s, leading to the lack of the three-fold axis. To confirm whether the low-temperature phase maintains a kagome-like network structure or not, we estimate the overlap integrals between the singly occupied molecular orbital wave functions of the MPYNN molecules by the extended Huckel method. The result is that all the overlap integrals are modified below T-s, suggesting that the system below T-s cannot be regarded as the uniform S = 1 kagome antiferromagnet.

DOI： 10.1143/JPSJ.73.796

Structural phase transition of theta-(BEDT-TTF)(2)RbZn(SCN)(4) under high pressure 査読

M Watanabe, Y Noda, Y Nogami, H Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 4 ) 921 - 925 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：PHYSICAL SOC JAPAN

theta-(BEDT-TTF)(2)RbZn(SCN)(4) is known as a two-dimensional organic conductor exhibiting a metal-insulator phase transition associated with a charge ordering phenomena at T-MI = 200 K under ambient pressure. The transition temperature increases with applied pressure and reaches room temperature at 1.1 GPa. The structural change by pressure induced phase transition was investigated by X-ray diffraction using synchrotron radiation. A superlattice formation of 2c was found above 1.1 GPa. A single crystal structural analysis taking account of the superlattice was carried out at 1.2 GPa. Displacements of BEDT-TTF molecules were found to be similar to the displacements in the low temperature phase at the ambient pressure. However, the shrinkage of the c-axis under pressure was four times as large as that under cooling at the transition point. Decreases in the intermolecular distances between BEDT-TTF molecules resulted in increases of the intersite Coulomb energies V and an increase of the electric bandwidth W. U/W (U: on-site Coulomb energy) decreased as a result of an increase of W. Such a change of U/W is obstructive to the enhancement of the charge ordered phase. This indicates that an effect of V is indispensable to the charge-ordered phase in this material.

DOI： 10.1143/JPSJ.73.921

Transfer integrals and the spatial pattern of charge ordering in theta-(BEDT-TTF)(2)RbZn(SCN)(4) at 90 K 査読

M Watanabe, Y Noda, Y Nogami, H Mori

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 ( 1 ) 116 - 122 2004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

theta-(BEDT-TTF)(2)RbZn(SCN)(4) is a two-dimensional organic conductor exhibiting a metal-insulator transition at T-MI = 200 K. This insulating charge ordered state below T-MI was investigated by a single crystal structural analysis taking account of the superlattice formation below T-MI. A large displacement (about 0.2 Angstrom) of BEDT-TTF molecules associated with the transition was found. Transfer integrals between BEDT-TTF molecules were also calculated from the structural data. The two-dimensional net of transfer integrals above T-MI was modulated into the quasi one-dimensional transfer integral chain by the superlattice formation below T-MI. The ionicities of BEDT-TTF molecules are estimated from the intramolecular bond length distribution. As a result, charge disproportionation between BEDT-TTF molecules was found, and the ionicity was 0 to +0.2 and +0.8 to +1.0 respectively. The hole-rich sites are laid on the quasi one-dimensional transfer integral chain. We conclude that the spatial pattern of charge ordering is a stripe alternating along the c-axis.

DOI： 10.1143/JPSJ.73.116

X-ray study of modulated structures of beta '-CuxV2O5 (x=0.29,0.39) 査読

N Nagao, Y Nogami, K Oshima, H Yamada, Y Ueda

PHYSICA B-CONDENSED MATTER 329 713 - 714 2003年5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

High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one-dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q(0) = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5. For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observed. A three-fold superlattice structure with q(1) = (0, 0.333, 0) appears below 210 K. An incommensurate modulated structure with q(2) = (0, 0.26-0.29, 0) coexists below 175 K, whose satellite intensity and b* component Q(b) have temperature and passing-time dependencies between 140 and 175 K. The competition between q(1) and q(2) modulations was also observed. It seems that the q(2) is deeply related to the physical property change between 140 and 180 K confirmed by the decrease in the magnetic susceptibility and the increase in the resistivity. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02021-5

High field Fermi surfaces studied by AMRO in eta-Mo4O11 査読

K Oshima, T Kambe, Y Nogami, T Sasaki

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 18 ( 1-3 ) 198 - 199 2003年5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 high field Fermi surface in eta-Mo4O11 at low temperatures has been studied by the Angle-dependent Magnetoresistance Oscillation (AMMO) method (Organic Super Conductors, Springer, Berlin, 1998, p. 455). The Shubnikov-de Haas (SdH) oscillation so far obtained shows existence of the several closed surfaces, but the results only give the area of the pockets. The AMMO result at high fields in the plane perpendicular to the crystal b-axis shows the angle-dependent resistance oscillation together with the SdH oscillations. We see no clear AMMO for the fields in the plane perpendicular to the c-axis. The results indicate the existence of very anisotropic Fermi surfaces, which are expected from the Fermi surface model (Chem. Rev. 91 (1991) 965) taking into account the lower temperature CDW nesting vector q(2). (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00964-5

Effects of tungsten doping on the CDW states of eta-Mo4O11 査読

T Kambe, S Tsuboi, N Nagao, Y Nogami, K Oshima

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 18 ( 1-3 ) 196 - 197 2003年5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 eta-Mo4O11 system shows successive CDW transitions due to its two-dimensional Fermi surface instability. We find that the lower temperature CDW-II transition easily disappears by doping a small amount of W atoms (less than 0.2%/Mo), though the higher temperature CDW-I transition is weakly depressed. The W atoms possibly substitute both the intra- and the inter-layer Mo sites. The doping effectively reduce the carrier compensation, leading to the suppression of TCDW-I. Moreover, the interlayer coherence between the intralayer two-dimensional CDWs may be destroyed by the substitution between the layers since the modulation of CDW-II state has an interlayer component. The resistivity along the conducting plane follows "log T" dependence below 10 K, suggesting that the W atoms doped within the layer should induce the Anderson-type charge localization. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00963-3

Shubnikov-de Haas oscillations and Fermi surface of tau-phase conductors 査読

T Konoike, K Iwashita, Nakano, I, H Yoshino, T Sasaki, Y Nogami, JS Brooks, D Graf, CH Mielke, GC Papavassiliou, K Murata

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 18 ( 1-3 ) 188 - 189 2003年5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

tau-phase organic quasi-two-dimensional conductors have a 4-fold single Fermi surface (FS) from band calculation. At low temperature, the resistivity turns into semiconducting, whereas Shubnikov-de Haas oscillations (SdH) have been observed. The SdH signal includes two frequencies that are inconsistent with the band calculation. Recently, we found the superstructure of this salt below 245 K by X-ray study. This result may explain the contradiction between observation and calculation for the FS. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)01004-4

X-ray study of modulated structures of beta '-CuxV2O5 (x=0.29,0.39)

N Nagao, Y Nogami, K Oshima, H Yamada, Y Ueda

PHYSICA B-CONDENSED MATTER 329 ( 329 ) 713 - 714 2003年5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

High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one-dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q(0) = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5. For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observed. A three-fold superlattice structure with q(1) = (0, 0.333, 0) appears below 210 K. An incommensurate modulated structure with q(2) = (0, 0.26-0.29, 0) coexists below 175 K, whose satellite intensity and b* component Q(b) have temperature and passing-time dependencies between 140 and 175 K. The competition between q(1) and q(2) modulations was also observed. It seems that the q(2) is deeply related to the physical property change between 140 and 180 K confirmed by the decrease in the magnetic susceptibility and the increase in the resistivity. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02021-5

Shubnikov-de Haas oscillations and low temperature electronic structure in tau-phase conductors 査読

T Konoike, K Iwashita, Nakano, I, H Yoshino, T Sasaki, T Takahashi, Y Nogami, JS Brooks, D Graf, CH Mielke, GC Papavassiliou, K Murata

SYNTHETIC METALS 135 ( 1-3 ) 615 - 616 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：ELSEVIER SCIENCE SA

tau-phase organic quasi-two-dimensional conductors have a 4-fold single Fermi surface (FS) from band calculation. At low temperature, the resistivity turns into semiconducting, whereas Shubnikov-de Haas oscillations have been observed. The amplitude of the oscillation is quite large because the system is near the quantum limit (N=2-state) under -27 T. The observed oscillations include two frequencies that are inconsistent with the band calculation. The reason of this discrepancy may be explained by the reconstruction of the FS. In this work, we examined very high magnetic field transport property up to 60 T and reconsider the low temperature crystal structure of this salt by diffuse X-ray study.

DOI： 10.1016/S0379-6779(02)00797-X

Superlattice structural analysis of (TTM-TTP)I-3 at low temperatures 査読

Y Nogami, T Kambe, N Fujimura, K Oshima, T Mori, T Kawamoto

SYNTHETIC METALS 135 ( 1-3 ) 637 - 638 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：ELSEVIER SCIENCE SA

The title quasi one-dimensional conductor with a half-filled energy band shows two kinds of modulated structures q(1) of (0 0 0.5) below 160 K and q(2) of (0.5 0 0.5) below 100 K. These wave vectors can nest Q1D Fermi surface. Two kinds of superlattice structures were solved using X-ray. In both cases, enhanced displacements of I-3 ions were observed. Their possible origins and their effects on the physical properties were discussed.

DOI： 10.1016/S0379-6779(02)00755-5

Investigation of X-ray diffuse scattering in theta-(BEDT-TTF)(2)RbM '(SCN)(4) 査読

M Watanabe, Y Noda, Y Nogami, H Mori

SYNTHETIC METALS 135 ( 1-3 ) 665 - 666 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：ELSEVIER SCIENCE SA

The modulated structure of theta-(BEDT-TTF)(2)RbM'(SCN)(4); (M'=Zn, Co) were investigated by X-ray diffraction method. theta-(BEDTTTF)(2)RbM'(SCN)(4) are two-dimensional organic conductors which exhibit metal-insulator transition at 210 K. The insulating phase is known as a charge ordered state. Above T-MI = 210 K, diffuse rod of q=(1/3 k 1/4) was found. Below T-MI, there are some differences depending on the sample cooling speed. In the slow-cooled-state (0.2 K/min), the diffuse rod of q=(1/3 k 1/4) disappears and is replaced by superlattice of c*/2. In the rapid-cooled-state (5-6 K/min), the structural phase transition at T-MI becomes imperfect. The diffuse rod of q remains below T-MI and the lattice modulation of c*/2 is disordered in the direction of inter-conducting-layer.

DOI： 10.1016/S0379-6779(02)00769-5

Fermi surface and low temperature structure in (DMET-TSeF)(2)Au(CN)(2) 査読

K Kato, K Oshima, T Kambe, Y Nogami, T Sasaki, M Motokawa, R Kato

SYNTHETIC METALS 135 ( 1-3 ) 577 - 578 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：ELSEVIER SCIENCE SA

The title compound is one of the DMET-TSeF salts which are quasi-one-dimensional organic metals at room temperatures. We show that the compound has a closed Fermi surface using the angle-dependent magnetoresistance oscillation (AMRO) method together with magnetoresistance and magnetization quantum oscillation measurements at low temperatures. By the X-ray measurement, we confirm that the structural phase transition observed around 180 K is related to the anomaly observed in the temperature dependence of the resistivity [1]. The nesting vector has the direction of 0.5a*+0.5c*. The obtained low temperature closed Fermi surface has about 4 % of the first Brillouin zone area. The AMRO data show the existence of a very anisotropic Fermi surface where the diameter perpendicular to the most conducting a direction is about 0.5 c*. The possible origin of the low temperature closed Fermi surface is discussed and the relation to the ordering of anion molecules is considered as the probable reason.

DOI： 10.1016/S0379-6779(02)00738-5

Magnetic investigation of itinerant and local hybrid spins system, (CHTM-TTP)(2)TCNQ 査読

T Nakamura, M Taniguchi, Y Misaki, K Tanaka, Y Nogami

SYNTHETIC METALS 133 441 - 442 2003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

EPR measurements of a new two-component organic conductor, (CHTM-TTP)(2)TCNQ, were performed. This salt shows two drastic successive phase transitions at low temperatures. The electronic phases of the title salt are discussed by microscopic point of view. The contributions of the two-spin species of the magnetic properties are separated. Possibility of cooperative phenomena in the two-spin system with itinerant and localised moments is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0379-6779(02)00274-6

　前のページ - 次のページ　

1
2
3
4
5
6
7