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Tetsu Ito, Makoto Tomita
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2493-2496
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The excitation pulse energy dependence of the gain volume in an amplifying and scattering medium was examined using a two-beam spatial-correlation method. The volume increased with 1/3 power of the excitation pulse energy in the weak excitation region, and then approached a critical value when the excitation energy was further increased. Numerical simulations explain the experimental results well, and a phenomenological model dealing with the total excitation in the gain volume via a rate equation is also discussed in order to explain the dependence.
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Sousuke Nishiura, Yositake Takane
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2497-2500
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We study the superconducting pairing correlation (SPC) effect on the resonant tunneling through an ultrasmall metallic grain with a gate electrode. The resonant conductance peaks appearing with an increase or decrease of the gate voltage are accompanied by the transition of the total electron number N on the grain, such as N ↔ N ± 1. We focus our attention on the tunneling resonance associated with an odd-N state. In the absence of the SPC effect, the structure of the zero-bias resonant conductance peak for N ↔ N - 1 is equivalent to that for N ↔ N + 1. It is shown that due to the interplay between the SPC effect and the nonuniform spacings of single-particle energy levels, we expect a notable difference between the two peak structures.
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Hiroshi Matsui, Hideaki Tsuchiya, Eiichi Negishi, Hiroshi Uozaki, Yusu ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2501-2504
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The temperature dependence of the microwave conductivity σ
1 and dielectric constant ε
1 has been measured on λ-(BEDT-TSF)
2FeCl
4 by a cavity perturbation method at 16.3 GHz, employing the TE
011 resonant mode. In spite of the highly metallic state above the metal-to-insulator (MI) transition at T
MI = 8.3 K, a novel ferroelectric-like response is observed in ε
1c along c at high temperatures from T
MI to T
FM = 70 K, which is enhanced to the order of 10
3 just above T
MI. Then a transition from a ferroelectric-like to paraelectric-like state with ε
1c ∼ 45 takes part in the MI transition. In contrast to the dc conductivity, σ
1c becomes much more conductive as considered by a collective mode. The ferroelectric-like response is associated with the dynamical response of the charge degrees of freedom in the π electronic system. An absence of these dielectric and thermodynamical anomalies in the nonmagnetic Ga analogue indicates the importance of the π-d interaction for the ferroelectric-like state as well as the MI transition.
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Masashige Matsumoto
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2505-2508
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Impurity nuclear spin relaxation is studied theoretically. A single impurity generates a bound state localized around the impurity atom in unconventional superconductors. With increasing impurity potential, the relaxation rate T
1-1 is reduced by the impurity potential. However, it has a peak at low temperatures due to the impurity bound state. The peak disappears at non-impurity sites. The impurity site NMR measurement detecting a local electronic structure just on the impurity atom is very useful for identifying the unconventional pairing states.
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Hirotaka Manaka, Isao Yamada, Takao Kikuchi, Kiyoko Morishita, Katsuno ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2509-2512
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The dependence of optical linear birefringence Δ n on temperature T was measured on a single crystal of (CH
3)
2CHNH
3CuCl
3, which consists of ferromagnetic-antiferromagnetic (F-AF) alternating Heisenberg chains with S=1/2. The curve of dΔ n(T)/d T showed a large peak near 25 K and a small shoulder near 45 K. The presence of these two anomalies is qualitatively similar to the theoretical curve of the magnetic specific heat in ferromagnetic-dominant F-AF chains.
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Ming-Fa Lin, Ming-Yang Chen, Feng-Lin Shyu
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2513-2516
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The inter-π-band electronic excitations of AB-stacked nanographite ribbons are studied within the self-consistent-field approach. Such excitations directly reflect the characteristics of the π-electronic structure. They depend on the magnitude (q) and the direction (θ) of the transferred momentum, the edge structure, and the stacking sequence. The loss function exhibits several peak structures. The pronounced peak, with frequency larger than 5 eV, is identified as the π-electronic collective excitations. The π plasmons exhibit highly anisotropic behavior. They are almost absent, when the transferred momentum is perpendicular to the graphitic plane (θ=90
º). However, their frequencies at small θ are not sensitive to the change in the stacking sequence.
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Takashi Kobayashi, Jun-ichi Hamazaki, Mitsuyoshi Arakawa, Hideyuki Kun ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2517-2520
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The time-resolved photoluminescence spectrum of a polythiophene derivative has been analyzed from the viewpoint of the vibronic structure and its dynamics. We found that the photoluminescence (PL) originates from two vibronic coupled states which consist of the odd-parity 1B
u component and the even-parity 2A
g component. Since the fluorescences from the two states have different time constants and different vibronic structures, the PL shows a biexponential decay and a spectral change.
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XiaoJun Liu, Yutaka Moritomo, Arao Nakamura, Takuya Hirao, Shuji Toyaz ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2521-2524
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We have observed a photoinduced phase transition (PIPT) in a spin-crossover Fe (II) complex Nafion-[Fe(Htrz)
3] film (Nafion is an ion exchange polymer film, and Htrz=1, 2, 4-1H-triazole) from a low-spin (LS) state (S=0) to a high-spin (HS) state (S=2) below 150 K. The phototransferred HS state relaxes to the initial LS state, exhibiting a nonexponential time behavior, which has been interpreted in terms of the critical nucleation and subsequent growth of the LS clusters. We have also observed that the decay time τ
c is approximately temperature-independent in the low temperature range of 4.2-20 K, and then decreases exponentially with temperature.
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Zuo-Nong ZHU Weimin, Zuo-Min ZHU
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2525-2530
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Stationary solitons of the fifth order singularly perturbed KdV-type equation are investigated. The second order approximate solution to fifth order singularly perturbed KdV-type equation and third order approximate solution to fifth order singularly perturbed KdV equation are obtained. It is shown that the properties of stationary solitons are dependent on nonlinear coefficient α and power p, the coefficient μ of 3-order dispersion and perturbed coefficient ε.
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Yukiko Umeno
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2531-2541
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The algebraic structure of the 1D Hubbard model is studied by means of the fermionic R-operator approach. This approach treats the fermion models directly in the framework of the quantum inverse scattering method. Compared with the graded approach, this approach has several advantages. First, the global properties of the Hamiltonian are naturally reflected in the algebraic properties of the fermionic R-operator which is a local operator acting on fermion Fock spaces. In particular, SO(4) symmetry and the invariance under the partial particle-hole transformation are shown. Second, a genuinely fermionic quantum transfer matrix (QTM) can be constructed in terms of the fermionic R-operator. By use of the algebraic Bethe ansatz, the fermionic QTM is diagonalized and its properties are discussed.
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Takao Yamamoto
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2542-2549
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The relaxation process of vicinal surface induced by the attachment-detachment mechanism is described in terms of the Ginzburg-Landau-Langevin (GLL) equation based on the harmonically-interacting step picture. To analyze the relaxation process, we pay attention to the three quantities, the step deformation width, the step diffusion length and the diffusion length of the system. These quantities are expressed in terms of two universal scaling functions and five system-specific constants. The GLL equation contains only three system specific parameters. Therefore, there must be two relations among the five constants and the relations
do not depend on the details of vicinal surface. The two relations are verified by a Monte Carlo simulation. It shows the quantitative validity of the GLL equation. The GLL equation is rewritten in a universal form
not depending on the microscopic dynamics by regarding the (squared) diffusion length of the system as the time.
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Norihiro Ihara, Shun-ichi Yoshida, Koh Wada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2550-2558
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The cluster variation method (CVM) is applied to the Ishibashi model for ammonium dihydrogen phosphate (NH
4H
2PO
4) of a typical hydrogen bonded anti-ferroelectric crystal. The staggered and the uniform susceptibility without hysteresis are calculated at equilibrium. On the other hand, by making use of the natural iteration method (NIM) for the CVM, hysteresis phenomena of uniform susceptibility versus temperature observed in experiments are well explained on the basis of local minimum in Landau type variational free energy. The polarization P curves against the uniform field are also calculated.
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Shuichi Yagi, Tetsuo Nagata
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2559-2567
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Absolute values of the total-apparent, total-counting, and charge separated partial cross sections have been measured for electron impact ionization of free atoms of Ce, Nd, Sm, Gd, Dy, Er and Yb. The electron energies have ranged from the single ionization threshold to 900 eV. Absolute total cross sections were determined with a crossed electron-atom beam assembly combined with time-of-flight velocity and oscillating crystal sensor accumulation measurements of target atoms. The relative partial cross sections were obtained separately with a magnetic deflection mass selector, and they were normalized to the total cross sections. The absolute cross sections have been determined with accuracy 23-33% depending on the target atom. Some of the single ionization cross section curves show complicated resonance-like structure in the region of 4f ionization thresholds. The 4d ionization exhibits a peak of shape resonance feature in the Ce
3+ and Nd
3+ curves, but the peak becomes less prominent with the increase in the atomic number Z and disappears beyond the Eu atom; this may be attributed to the lowering of the centrifugal barrier potential for f electrons in higher Z elements. Evidences of shake-up and/or shake-off processes associated with 5p or 5s electrons are observed in the quadruple ionization.
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Franois B. Pelap, Timoléon C. Kofané, Nikos Flytzanis, M ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2568-2577
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Adding dissipative elements to a discrete biinductance transmission line which admits both low frequency (LF) and high frequency (HF) modes, dynamics of a weakly nonlinear modulated wave is investigated theoretically and numerically. In the semidiscrete approximation using a proposed decoupling ansatz for the voltage of the two different cells, it is shown that the original differential-difference equation for this transmission line can be reduced to the complex Ginzburg-Landau (CGL) equation. The modulational instability criterion for sinusoïdal waves has been recovered. Furthermore, numerical simulations show that the theoretical predictions are well reproduced.
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Masahiko Sato, Satoshi Hamaguchi, Masahiro Wakatani
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2578-2587
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
For negative shear cylindrical tokamaks, nonlinear behavior of double tearing modes (DTMs) with (m,n)=(3,1), (2,1) and (1,1) has been studied for 0.9<q
min<3, where q
min is a minimum safety factor and m (n) is a poloidal (toroidal) mode number. For Δ r<0.1, the linear growth rate of DTM, γ, scales as γ ∝ S
-1/3 approximately, where Δ r is a distance between two resonant surfaces normalized with a plasma radius. For Δ r>0.4, γ ∝ S
-3/5, and transition behavior is seen for 0.1<Δ r <0.4. It is noted that nonlinear destabilization of DTM is seen for this case, which means that DTM produces a completely flat q-profile or a full reconnection within the external resonant surface, although γ ∝ S
-3/5 roughly in the linear phase. Generally the lower m mode generates the full reconnection for the wider distance between the two resonant surfaces.
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Hee Tae Jeong, Yong Chan Cho, Chae Ryong Cho, Se-Young Jeong
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2588-2592
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
By the group-theoretical method, the permissible domain walls for all 94 ferroelastic species were analyzed. This method is not only consistent with wall equations using Sapriel's strain tensor method, but also provides additional information such as the types of wall, the point groups of each domain, and the configurations of twin structures. The permisible domain walls for a given domain pair were characterized by one or more symmetry elements which are defined as the set of wall characterizing elements (WCE). We found that the Sapriel's W wall was characterized by mirror plane or two or more symmetry elements, while the W
′ wall by only one rotational symmetry element. With the help of the crystallographic consideration, the group-theoretical analysis showed that all permissible domain walls are crystallographically prominent planes with fixed indices. They are represented by W
m, W
b, W
f, or combinations of them, depending on the WCE. Most notably, the existence of a four-fold wall, W
f, is suggested for the first time.
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Takanori Ito, Kazume Nishidate, Mamoru Baba, Masayuki Hasegawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2593-2597
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Properties of (10, 10) single-walled carbon nanotubes under uniaxial pressure are investigated by means of pressure-controlled molecular dynamics simulations using an order-N tight-binding method. We use an extended Andersen method in order to control pressure of system. This scheme allows us to investigate the pressure-dependence of structural stability as a function of time in the presence of many-body quantum mechanical effect. At small strains, the potential energy of the carbon nanotube increases in accordance with the Hooke's law. In this elastic regime, the carbon nanotube keeps straight as a whole. The finite temperature effects on the strains are analyzed.
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Hideo Takeuchi, Kohji Mizoguchi, Masaaki Nakayama, Kazuyoshi Kuroyanag ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2598-2602
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We have investigated coherent longitudinal optical (LO) phonons in GaSb/AlSb superlattices. The coherent AlSb-like LO phonon in the barrier layer and the coherent GaSb-like LO phonon in the well layer have been simultaneously observed. The GaSb-like LO phonon exhibits a cosine-type oscillation, which is the dominant signal. We have analyzed the initial phase of the AlSb-like LO phonon by plotting the imaginary part of the Fourier-transform components as a function of the real part, the so-called Cole-Cole's plot. We have found from this plot that the difference in the initial phase between the GaSb-like and AlSb-like LO phonons is about 90 degrees: The AlSb-like LO phonon has a sine-type oscillation. This difference in the initial phase indicates the difference in the generation mechanism between the coherent GaSb-like and AlSb-like LO phonons. We discuss the generation mechanism based on some proposed models.
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Tomoko Imasaka, Shoji Hirokawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2603-2612
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
A clathrate consists of both a `host' system and a `guest' system composed of the enclosed molecules. Treating the guest system as a diluted dipolar one, we have investigated the effects on orientational phase transitions of the cavity occupancy x, a crystal field W due to host molecules, the difference between atom-atom potentials and the ignorance of those contributions by the host system which are not involved in W. It is shown that self-consistency makes the transition temperature T
c a nonlinear function of x. The occurrence of a successive phase transition is shown to depend on the higher order terms of W and on the difference in the potential model. It is also clarified that the host system may affect the estimation of T
c. We have further investigated to what extent classical statistical mechanics is applicable at low temperatures. Results are discussed in relation to the experiments.
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Ted Janssen, Yoshihiro Ishibashi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2613-2615
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The discrete four-sublattice model previously proposed for reproducing the lattice instabilities in A
2BX
4-type crystals is reduced to a two-sublattice model. Eigenfrequencies and the associated eigenvectors of the dynamical matrix are given analytically for general k values. The conditions on the interaction parameters for the appearance of incommensurate phase transitions are clarified.
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Hiroyuki Fujishiro, Shingo Kanoh, Hajime Yamazaki, Manabu Ikebe
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2616-2621
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The thermal conductivity κ(T), the diffusivity α(T) and the thermal dilatation dL(T)/L have been measured for Pr
0.65Ca
0.35MnO
3 and Pr
0.65Ca
0.35(Mn
1-ZCo
Z)O
3 (Z=0.02-0.10) crystals under the magnetic field of up to 5 T. By application of high magnetic fields or Co substitution for the Mn site, the ferromagnetic metallic (FM-M) state are induced and κ(T) and α(T) are drastically enhanced below the ferromagnetic transition temperature T
F. The enhancement is closely related to the relaxation of the local Jahn-Teller lattice distortion due to the increased hole mobility in the FM-M phase.
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Toshinori Abe, Tadao Ishii
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2622-2625
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The temperature dependent frequency exponent s
′ in the ionic conductivity Re σ(ω)=σ(0)+A
′ω
s′ is investigated by the relaxation mode theory in one-dimensional random lattices with exponential, uniform and normal distributions of activation energies: For the exponential distribution, Bernasconi ηl. analytically obtained s
′≈ s
B=(1-T/T
m)/(1+T/T
m) in the effective medium approximation within the range T<T
m. The present theoretical investigation concludes that (1) the obtained result s
′ is reproduced by s
B approximately for T<0.5T
m, and (2) the exponential distribution is not essential to obtain s
′≈ s
B: s
′ can be approximated by s
B better in the case of uniform distribution.
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Chi-Chuan Hwang, Yeau-Ren Jeng, Yu-Lin Hsu, Jee-Gong Chang
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2626-2632
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
This study uses molecular dynamics simulations to elucidate the spreading behavior of a liquid droplet on a rough solid surface. The Lennard-Jones potential energy model is adopted as the interaction model between the liquid and the solid molecules. The paper considers two types of rough surface: periodic and random. These surfaces are characterized by their roughness height and their spatial variation. For a periodic surface, the roughness height is defined by the amplitude, A, while for a random surface, it is defined in terms of the standard deviation of the roughness height, σ. Regarding the spatial variation of the surface, a periodic surface is characterized by the wavelength, λ, while the random surface is characterized by its autocorrelation length, L. Simulation results indicate that the characteristics of the rough surface can significantly influence spreading behavior, in terms of final equilibrium time, spreading radius, and spreading topography. It is observed that the effects of roughness height and spatial variation are broadly similar for both periodic and random surfaces. It is found that increasing roughness height and decreasing spatial periodicity both prolong the final equilibrium time, and that the final spreading radius decreases with increasing roughness height and increases with larger spatial periodicity.
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Tomokazu Matsuo, Hidetoshi Fukuyama
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2633-2644
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Based on the Berezinskii's diagram method, the density of states (DOS) of a bond disordered system has been calculated in the presence of the dimerization and the staggered field. It is found that the DOS near the center of the band behaves anomalously and that it is indicated that this feature is the cause of the coexistence phase of antiferromagnetism (AF) and dimerization in the disordered quasi-one-dimensional spin-Peierls (SP) system CuGe
1-ySi
yO
3.
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Baigeng Wang, Jian Wang, Hong Guo
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2645-2651
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We present a theoretical analysis of the nonlinear bias and temperature dependence of current-voltage characteristics of a spin-valve device which is formed by connecting a nonmagnetic system to two ferromagnetic electrodes whose magnetic moments orient at an angle θ with respect to each other. The theory is based on nonequilibrium Green's function approach and focused on current perpendicular to plane geometry. Coulomb interaction has been taken into account explicitly at the Hartree level. We derive a formula in closed form for current flowing through the device in general terms of bias and temperature. In the wideband limit we report exact results for the tunneling magnetoresistance (TMR) junction nonlinear I-V curve as a function of θ. We also report the conductance slope at zero bias as a function of temperature for which experimental results reported an anomalous behavior.
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Kentaro Nomura, Daijiro Yoshioka
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2652-2656
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The effects of randomness are investigated in the fractional quantum Hall systems. Based on the Chern-Simons Ginzburg-Landau theory and considering relevant quasi-particle tunneling, the edge state network model for the hierarchical state is introduced and the plateau-plateau transition and the liquid-insulator transition are discussed. This model has duality which corresponds to the relation of the quantum Hall liquid phase and the Hall insulating phase and reveals a mechanism of plateau transition in the weak coupling regime.
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Hajime Matsumura, Tsuneya Ando
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2657-2665
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The conductance of carbon nanotubes with a Stone-Wales defects composed of two pentagon-heptagon pairs is calculated in an effective-mass approximation. The presence of topological defects is represented as a nonlocal potential. The results obtained in the k · p scheme agree with those in a tight-binding model.
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Akira Oguri
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2666-2681
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Transport through small interacting systems connected to noninteracting leads is studied based on the Kubo formalism using a Éliashberg theory of the analytic properties of the vertex part. The transmission probability, by which the conductance is expressed as g = (2e
2/h) ∫ dε (- ∂ f / ∂ ε) T(ε), is introduced for interacting electrons. Here f(ε) is the Fermi function, and the transmission probability T(ε) is defined in terms of a current vertex or a three-point correlation function. We apply this formulation to a series of Anderson impurities of size N (=1, 2, 3, 4), and calculate T(ε) using the order U
2 self-energy and current vertex which satisfy a generalized Ward identity. The results show that T(ε) has much information about the excitation spectrum: T(ε) has two broad peaks of the upper and lower Hubbard bands in addition to N resonant peaks which have direct correspondence with the noninteracting spectrum. The peak structures disappear at high temperatures.
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Hiroyuki Shima, Kousuke Yakubo, Tsuneyoshi Nakayama
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2682-2688
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We numerically study the spatial profiles of wavefunctions and the frequency dependences of the ac conductivity σ(ω) for two-dimensional electron systems subject to long-range random magnetic fields (RMF) with zero mean. It is found, for a weak RMF, that amplitudes of the wavefunction are almost uniformly distributed over the system, and the ac conductivity is described by the Drude theory. Under a strong RMF, quantum states corresponding to classical snake trajectories can be strongly localized, which implies that the quantum interference along zero magnetic field contours is crucial for understanding electron transport. In this case, the conductivity σ(ω) rapidly increases in the frequency regime lower than a crossover frequency ω
c and decreases linearly for ω » ω
c. The crossover frequency is governed by the localization length of the electron eigenstate at the Fermi energy.
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Tohru Kohda, Shinji Ono, Michisuke Kobayashi, Hiroshi Iyetomi, Shoji K ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2689-2693
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The tight-binding electronic band calculations of β-Ag
3SX (X=I, Br) are carried out in order to clarify the high ionic conductivity of silver ions. The d bands of Ag ions are much more weakly coupled with the p bands of halogen ions, than with the p bands of S ions. The strength of p-d hybridization is discussed to connect with the activation energy for the ionic conduction. It is shown that the high ionic conductivity of β-Ag
3SX (X=I, Br) primarily stems from the weakness of the p-d hybridization.
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Takuji Nomura, Kosaku Yamada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2694-2697
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We investigate pairing symmetry in quasi-one-dimensional organic superconductors, solving Eliashberg's equation within third order perturbation theory for a repulsive Hubbard model. According to the calculation results, spin-singlet state is expected to give higher transition temperature than spin-triplet one and the vertex corrections reduce the transition temperature for the spin-singlet case. It is shown that the contributions of antiferromagnetic spin fluctuations dominate strongly the momentum dependence of the effective pairing interaction for both of the spin-triplet and the spin-singlet pairing cases.
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Kazuhiro Kuboki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2698-2702
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Effects of band structure on the symmetry of superconducting (SC) states are studied. We show that various symmetries of SC states are possible within the same type of interaction when the shape of the Fermi surface is changed. As a simple model we consider a square lattice system with a nearest-neighbor attractive interaction, and find that the spin-triplet ((p
x + i p
y)-wave) and spin-singlet (d- or s-wave) SC states, and states with their coexistence (d + i p
y, s + i p
y) can be stabilized if the electron density (and thus the Fermi surface) is changed. By taking into account the interlayer attractive interaction in this model, the stability of interlayer-pairing states with line nodes is examined, and its relation to the SC state of Sr
2RuO
4 is discussed.
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Yoshiki Nakanishi, Takeshi Matsumura, Fumihiko Takahashi, Takuo Sakon, ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2703-2710
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Magnetic properties of TmS have been examined in high magnetic fields by means of resistivity, specific heat and magnetization measurements using a high quality single crystal. The high-field magnetization measurements indicate that the magnetization for H || <001> is quite suppressed at high fields. The observed results can be explained reasonably by taking into consideration of O
20-type ferro electric quadrupolar (FQ) interactions and the crystalline electric field effect. The new phase which has been induced by applying magnetic fields, might be ascribed to the O
20-type FQ ordering. The established magnetic field-temperature phase diagram implies that the antiferromagnetic interaction and O
20-type FQ interaction coexist at low temperatures.
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Takeo Otsuka, Masahiro Yoshimaru, Kunio Awaga, Hiroyuki Imai, Tamotsu ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2711-2716
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We studied the impurity effects on the molecular spin ladder, (p-N-ethylpyridinium nitronylnitroxide cation (=p-EPYNN; S=1/2))·(bis(4,5-dithiolato-1,3-dithiole-2-thione) nickelate anion (=[Ni(dmit)
2]; S=1/2)), that involved a two-leg spin ladder of [Ni(dmit)
2] sandwiched by ferromagnetic chains of p-EPYNN, by making a solid solution system p-EPYNN · [Ni(dmit)
2]
1-x[Au(dmit)
2]
x with x≤q 0.5. Doping of the non-magnetic [Au(dmit)
2] increases Curie defects in the ladder and results in antiferromagnetic behavior of p-EPYNN. This can be explained by the antiferromagnetic domains on the p-EPYNN chain induced by the spin polarization around the impurity site on the [Ni(dmit)
2] spin ladder.
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Masugu Sato, Tetsuya Takeuchi, Kenji Watanabe, Shuzo Kawarazaki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2717-2723
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Neutron diffraction experiments with use of horizontal magnetic field have been carried out to study the magnetic structure of the ground state and the origin of the metamagnetism of the compound ErRu
2Si
2. Combination of the results of the previous magnetization measurements and of the present intensity measurements of several satellite reflections from a single-crystalline sample in null field leads to a conclusion that the ground-state magnetic structure consists of a double-q superimposed structure of long-period transverse modulations. The metamagnetism together with the response of the satellite reflections to magnetic field have been satisfactorily explained on the basis of this double-q structure under assumptions of strong Ising anisotropy and persisting molecular field.
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Nobuyuki Momozawa, Yukinobu Nagao, Shigenori Utsumi, Masahiko Abe, Yas ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2724-2732
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Magnetization measurements and neutron diffraction experiments were carried out on single crystals of Ba
2(Zn
1-xMg
x)
2Fe
12O
22, where x is the Mg concentration ranging from x=0 to 1.0. The Fe ions present in the octahedral sites have a tendency to decrease with increasing x. The configuration of Fe magnetic moments in the Mg-rich crystal is a distorted helimagnetic one consisting of large and small ferrimagnetic bunches. We have found that there are competing exchange interactions among Fe magnetic moments lying on the forth, fifth and eighth layers of Mg-rich crystal. The exchange integrals J
45, J
48 and J
58 were determined using the molecular field approximation: J
45/J
58=0.365± 0.008 and J
48/J
58=0.503± 0.016 at 9 K. These values provide a clear interpretation of the turn angle of the helix as well as the helimagnetic structure for the Ba
2(Zn
1-xMg
x)
2Fe
12O
22 system.
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Hiroyuki Yamase, Hiroshi Kohno
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2733-2745
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
On the basis of the picture of a quasi-one-dimensional (q-1d) Fermi surface (FS), recently proposed by authors for LSCO systems, spin excitation spectrum, Im χ(q,ω), is calculated in the `RPA' within the slave-boson mean-field approximation to the t-J model. It is found that Imχ(q,ω) shows both incommensurate (IC) and diagonal IC (DIC) peaks, whose realization does not depend on the existence of the d-wave gap. The peak positions do not change appreciably with ω and the sharp peaks survive down to the low hole doping rate. The d-wave gap suppresses both the IC peak and the DIC peak, but the degree of suppression as a function of ω is different between them. Taking these results together with results for the two-dimensional FS, we argue that essential features of magnetic excitation in LSCO systems can be understood in terms of the q-1d picture of the FS.
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Ryousuke Shiina
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2746-2756
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The effect of multipolar fluctuations on the quadrupolar phase transition in CeB
6 is investigated. The d
-1-correction to the mean-field solution of the multipolar Ruderman-Kittel-Kasuya-Yoshida (RKKY) model is analyzed in terms of a generalized Landau expansion of free energy, with d being the spatial dimension. It is shown that the multipolar fluctuations become strong and field-dependent when the model is close to the SU(4)-symmetric limit. As a result, various unusual phenomena around the transition are shown to be reasonably explained within the RKKY model. The realistic form of the interactions for CeB
6 is discussed on the basis of a quantitative comparison with experiments.
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Toshihiko Fukamachi, Keisuke Oda, Yoshiaki Kobayashi, Takeshi Miyashit ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2757-2764
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
139La-NMR/NQR measurements of La
3Ni
2O
7-δ (δ∼ 0.0 and δ∼ 0.08), and La
4Ni
3O
10 have been performed.
139La-NMR and transport and magnetic studies have also been carried out for Tl(La
2Sr
2)Ni
2O
9. Anomalous temperature (T) dependence of the longitudinal relaxation rates 1/T
1 has been found at temperatures T
A∼ (140-150 K) for all the systems. In Tl(La
2Sr
2)Ni
2O
9, there exists a transition to a magnetically ordered state at T∼ 20 K. The large broadening of the NMR spectra observed for Tl(La
2Sr
2)Ni
2O
9 below 20 K indicates that the system is in the charge ordered state in the temperature region between 20 K and T
A with localized magnetic moments at Ni sites. The NQR intensity of La
4Ni
3O
10 begins to decrease rapidly with decreasing T at T
A∼ 140 K and almost disappears at T∼ 120 K (wipeout). By arguing results of the present experimental studies, we propose that in all the systems with NiO
2 planes studied here exhibit similar type transitions to the charge ordered states at temperatures T
A, all of which are in the narrow T region around 140 K. It has also been found that all the systems exhibit resistivity anomalies in the T region of (450-550) K, which suggests that they have a tendency of similar type changes or transitions of their electronic states at the temperatures, too.
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Jun Kikuchi, Naohiko Kurata, Kiyoichiro Motoya, Touru Yamauchi, Yutaka ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2765-2773
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Low-frequency spin dynamics in the S=1/2 antiferromagnetic spin-chain compound α-VO(PO
3)
2 has been studied by means of
31P NMR. The nuclear spin-lattice relaxation rate 1/T
1 at the P site exhibits H
-1/2 dependence on the applied magnetic field (H) at temperatures (T) well above the intrachain coupling strength J/k
B = 3.50 K indicating one-dimensional diffusive spin dynamics. The diffusive contribution to 1/T
1 decreases on cooling as electronic spins acquire short-range antiferromagnetic correlations within the chain, and vanishes almost entirely around T ≈ J/k
B. This is accompanied by an apparent increase of the spin-diffusion constant from the value expected in the classical limit. On the other hand, the field-independent part of 1/T
1 increases with decreasing temperature, which may be a precursor for the true long-range antiferromagnetic ordering found below T
N = 1.93 ± 0.01 K.
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Keiichi Koyama, Makoto Yoshida, Dexin Li, Mitsuhiro Motokawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2774-2777
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Electron spin resonance measurements on single-crystal of GdP have been performed in the temperature range from 5 to 40 K and in the frequency range from 50 to 109 GHz to obtain microscopic information about the magnetic structure. The results obtained indicate that GdP is an “easy-plane” antiferromagnet with the magnetic moment lying in the {111} plane below the Néel temperature (∼18 K). The estimated values of the exchange field and the out-of-plane anisotropy field are μ
0H
E=4.5 T and μ
0H
A=1.7 T, respectively.
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Kenji Ohwada, Kazuma Hirota, Paul W. Rehrig, Peter M. Gehring, Beatriz ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2778-2783
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
Single crystals of the relaxor PZN-xPT display an enormously strong piezoelectric character. Recent x-ray scattering studies have revealed novel electric-field induced phase transitions in PZN-8%PT. As-grown crystals exhibit a rhombohedral structure that, under application of an electric field oriented along [001], transforms into a monoclinic (M
A) phase, and then irreversibly to another monoclinic (M
C) phase with increasing field strength. Since the latter phase change is very unusual, its transition sequence has been investigated by using triple-axis neutron scattering techniques so that the “skin effect” observed by x-ray scattering can be avoided, and the entire crystal bulk is probed. Contour maps of the elastic scattering have been mapped out in each phase in the (H0L) zone with high q-resolution. Increasing the field strength within the M
C phase induces a sharp c-axis jump around 15 kV/cm. This jump was observed easily with x-rays in previous studies, but it was not observed in 5 different crystals examined with neutrons. A subsequent high-energy x-ray study of the same crystals showed that the c-axis jump is distributed within the crystal volume, thereby washing out the jump. The observed R-M
A-M
C transformational path is in perfect accord with very recent first principles calculations by Bellaiche, Garcia, and Vanderbilt in the PZT system.
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Takeo Watanuki, Shinya Yoshioka, Masaru Kasahara, Timothy F. Crimmins, ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2784-2787
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The dispersion relation of the A
1 phonon-polariton of ferroelectric LiNbO
3 has been studied by the impulsive stimulated Raman scattering (ISRS) experiment improved with optical phase masks and heterodyne detection. A simple dispersion relation is revealed in contrast to the previous heterodyne ISRS study where several avoided crossing points were reported. The static dielectric constant obtained from the gradient of the dispersion curve with respect to the wave vector shows a good agreement with the previous dielectric measurement.
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Hideyuki Takahashi, Masaru Tsukada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2788-2792
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
We examined the structures and energies of 15 isomers of C
36 using the newly developed first-principles calculation based on the finite-element method (FEM). The Jahn-Teller distortion (D
6h→C
6v) for the isomer with D
6h symmetry is not confirmed in the present calculation, and the isomer with the lowest energy is found to be the one with D
2d symmetry. In experiments, C
36 is synthesized as C
36H
4 or C
36H
6. We calculated the stable structure of C
36H
x (x=2, 4, 6, 8) and searched a clue to the question why the hydrogenation process stops at the C
36H
6 stage. Consequently, we propose two hydrogenation way up to octahydrogenation. In examing the hydrogenation processes, we conclude C
36H
6 is still energetically reactive to hydrogenation.
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Yoshihiro Ishibashi, Minoru Fukui
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2793-2799
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
The traffic flows on two one-lane roads, crossing at a point, are studied on the basis of the local occupation probability method. The phase diagrams are constructed for the cases of various maximum car velocities. It has turned out that the phase diagrams consist essentailly of five regions.
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Masahiro Agu, Hideo Akabane, Takeshi Saito
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2798-2799
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
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Hisashi Kondo, Toru Moriya
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2800-2801
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
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Yukitoshi Motome, Nobuo Furukawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 70 巻 9 号 p.
2802-2803
発行日: 2001年
公開日: 2003/02/28
ジャーナル
認証あり
