Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 68, Issue 8
Displaying 1-50 of 67 articles from this issue
  • Namiko Mitarai, Hiizu Nakanishi
    1999 Volume 68 Issue 8 Pages 2475-2478
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We analyzed the stability of the uniform flow solution in the optimal velocity model for traffic and granular flow under the open boundary condition. It was demonstrated that, even within the linearly unstable region, there is a parameter region where the uniform solution is stable against a localized perturbation. We also found an oscillatory solution in the linearly unstable region and its period is not commensurate with the periodicity of the car index space. The oscillatory solution has some features in common with the synchronized flow observed in real traffic.
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  • Hidetoshi Katori, Tetsuya Ido, Makoto Kuwata–Gonokami
    1999 Volume 68 Issue 8 Pages 2479-2482
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We propose and demonstrate a novel far-off-resonance optical dipole trap (FORT) that is compatible with Doppler cooling. Strontium atoms are magneto-optically cooled and trapped by the spin-forbidden transition 1S0-3P1 at 689 nm, while the tight-focused infrared laser couples these two states to the respective dipole-allowed singlet and triplet states to generate the same amount of light shift. These designed light shifts for the cooling transition, enabling simultaneous Doppler cooling and dipole trapping, lead to the efficient loading of cooled atoms into the FORT with a few recoil energies. This scheme provides an important step towards the realization of quantum degenerate strontium atoms by purely optical means.
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  • Yutaka Shimomura
    1999 Volume 68 Issue 8 Pages 2483-2486
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    It is claimed in the subgrid-scale (SGS) modeling of incompressible turbulent flows that none of the (modified) Leonard terms, the (modified) cross terms, or their sums can be neglected, in principle, due to the constraint of material frame indifference in the limit of two-dimensional turbulence [C.~G. Speziale: Geophys. Astrophys. Fluid Dyn. 23 (1983) 69], and that the Clark model [R.~A. Clark, J.~H. Ferziger and W.~C. Reynolds: J. Fluid Mech. 91 (1979) 1] is consistent with this constraint. Furthermore, a family of dynamic SGS models consistent with this constraint is found, and specifically, a two-parameter dynamic SGS model is proposed as the most desirable member, whose expression for the SGS Reynolds stress asymptotically disappears in the limit of two-dimensional turbulence.
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  • Katsuhiko Hasebe, Takanao Asahi
    1999 Volume 68 Issue 8 Pages 2487-2490
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Spontaneous strain accompanied by the ferroelastic phase transition of the mixed crystal system [N1-xPx(CH3)4]2ZnBr4 (x=0, 0.05, 0.15, 0.44, 0.75, 0.85, 0.93, 1) was studied by X-ray diffraction. The deviation angle Δ β of the monoclinic angle β from 90°showed characteristic temperature dependence, where the sign of Δ β was chosen so that the configuration of ions in the ferroelastic phase was the same for all compositions. As the value of x increased to 0.15, the maximum value of Δ β increased and the slope in the low-temperature region decreased. At x=0.44, Δ β was almost temperature independent. Absolute values were very small at x=0.75. At x=0.85 it was negative throughout, and above the concentration it approximated the typical temperature dependence of [P(CH3)4]2ZnBr4. The transition temperature increased with increasing x. The phase transition changed from second order to first order one between x=0.85 and 0.93. Structure analysis revealed that the position of ions changed only slightly in the ferroelastic phase in each compound.
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  • Atsushi Tsuruta, Akito Kobayashi, Yoshiaki Ono, Tamifusa Matsuura, Yos ...
    1999 Volume 68 Issue 8 Pages 2491-2494
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We investigate electronic states in the multichannel degenerate Anderson lattice with the aid of the 1/N-expansion procedure. Inclusion of the self-energy in O(N0) leads to heavy electrons with degeneracy of channel and spin-orbit. In O(N-1), we find a T-linear term in the imaginary part of the self-energy of the conduction electrons at the Fermi level, in contrast to a T2-term as in the Fermi liquid or a constant term as in the non-Fermi liquid found in infinite dimensions. The disappearance of the imaginary part at T=0 is due to the intersite correlation effects that reflect the translational invariance. The Luttinger sum rule is proved to hold.
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  • Hiroyuki Suzuki, Takao Furubayashi, Guanghan Cao, Hideaki Kitazawa, Ak ...
    1999 Volume 68 Issue 8 Pages 2495-2497
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The thiospinel compound CuIr2S4 exhibits the metal-insulator (M-I) transition accompanied by the structural transition. In this work, compounds of Cu1-xZnxIr2S4 in the composition range 0≤ x≤ 0.5 were synthesized to examine the effects of excess electrons supplied by replacing Cu with Zn. The samples were investigated by measurements of X-ray diffraction, electrical resistance and magnetic susceptibility. The M-I transition temperature TMI decreases with increasing x. Results are discussed on the basis of the model of charge ordering for the insulating state. It was found that the samples with x≥q 0.3 show no M-I transition and exhibit superconductivity. The transition temperature TC is 2.8 K for x= 0.3 and 2.2 K for x= 0.5. The ground state of the system changes from insulating to superconducting with increasing Zn content.
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  • Kazuaki Iwasa, Yoshihito Arakaki, Masahumi Kohgi, Takashi Suzuki
    1999 Volume 68 Issue 8 Pages 2498-2501
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    In order to investigate the unusual magnetic properties of the low-carrier system CeSb, X-ray diffraction studies at low temperatures have been performed. Below the magnetic transition temperature of TN = 17 K, several X-ray satellite peaks and their temperature variations were observed, which indicate that the modulated structures of a crystal lattice coexist with the long-period magnetic structures in CeSb. The observed wave numbers of the lattice modulations and the satellite-peak intensities are explained by the periodical arrangement of short and long distances between magnetic layers. The short interlayer distance is due to enhancement of p-f mixing effect which is spatially restricted within the ferromagnetic layers of Γ 8-like Ce ions appearing in the lattice of Γ 7 Ce ions. The interlayer distance due to Γ 8-like state is shorter by 0.1% than that between normal Γ 7 Ce layers.
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  • Kentaro Nomura, Daijiro Yoshioka
    1999 Volume 68 Issue 8 Pages 2502-2505
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The transport properties of bilayer quantum Hall systems at ν=1/q, where q is an odd integer, are investigated. The edge theory is used for the investigation, because tunneling between the two layers is assumed to occur on the edge of the sample because of the bulk incompressibility. It is shown that in the case of the independent Laughlin state, tunneling is irrelevant when ν<1/2 in the low temperature and long wavelength limit. The temperature dependence of the two-terminal conductance of the system in which only one of the two layers is in contact with the electrode is discussed.
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  • Akito Kobayashi, Atsushi Tsuruta, Tamifusa Matsuura, Yoshihiro Kuroda
    1999 Volume 68 Issue 8 Pages 2506-2509
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Using the d-p model, we demonstrate that the pseudogap, which is induced by the superconducting fluctuation, plays key roles in the determination of the phase diagram observed in high-Tc superconducting materials. We take the pairing interaction mediated by the spin fluctuation and calculate the superconducting transition temperature Tc, the NMR relaxation rate 1/T1 and the single-particle spectrum by treating both the superconducting fluctuation and spin fluctuation in a consistent fashion. As temperature decreases, 1/T1T increases at high temperatures, and it reaches a maximum followed by a sharp drop in the underdoped region, due to the evolution of the pseudogap in the single-particle spectrum. The evolution is also consistent with those of ARPES experiments.
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  • Hiroki Tsuchiura, Yukio Tanaka, Masao Ogata, Satoshi Kashiwaya
    1999 Volume 68 Issue 8 Pages 2510-2513
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The superconducting state around a well-isolated nonmagnetic impurity in the high-Tc superconductors is studied using the two-dimensional t-J model. The spatial dependence of the order parameter and the local density of states are obtained from the numerical diagonalization of the Bogoliubov-de Gennes equation derived using the Gutzwiller approximation. We find a zero-energy peak in the local density of states around the impurity. Different from the previous results on a vortex or surfaces in the t-J model, the splitting of the zero-energy peak is not found. The zero-energy states corresponding to the zero-energy peak is approximately localized around the impurity.
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  • Yositake Takane
    1999 Volume 68 Issue 8 Pages 2514-2517
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The plasma mode in thin superconducting wires is studied within the random-phase approximation in the dirty limit at zero temperature. The plasma frequency ωp is calculated as a function of the wave number. In the limit of ωp << Δ /(h/2π) the result is in agreement with a nearly linear dispersion relation obtained by the phenomenological theory [Mooij and Schön: Phys. Rev. Lett. 55 (1985) 114.]. It is found that, except in the low-frequency limit, the phenomenological theory leads to an overestimation of ωp. The finite length of the sample limits the number of allowed modes in actual situations, and the corresponding plasma frequencies are quantized as ωpn (n=1, 2, …). Due to this quantization and a divergent state density at the gap edge, a sharp structure is shown to arise in the tunneling density of states at ε=ωpn+ Δ due to the plasmon exchange process.
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  • Satoru Awaji, Norio Kobayashi, Shinichi Sakatsume, Satoru Kunii, Masaf ...
    1999 Volume 68 Issue 8 Pages 2518-2521
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The high-field magnetization measurement of the antiferro (AF) magnetic compound NdB6, which has a small magnetic anisotropy in low magnetic fields, revealed an unexpected metamagnetic transition. This is observed only for H// ‹ 111 ›, while the magnetization curve for H// ‹ 100 › and ‹ 110 › is normal, as usually observed in an AF magnet with a small magnetic anisotropy. To our knowledge, this is the first example of the anisotropic magnetic field induced metamagnetic transition for a compound with a small magnetic anisotropy in low magnetic fields.
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  • Nobuo Furukawa
    1999 Volume 68 Issue 8 Pages 2522-2525
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    In order to study the magnetic excitation behaviors in colossal magnetoresistance manganites, a magnon-phonon interacting system is investigated. Sudden broadening of the magnon linewidth is obtained when a magnon branch crosses over an optical phonon branch. Onset of the broadening is approximately determined by the magnon density of states. Anomalous magnon damping at the Brillouin zone boundary observed in low Curie temperature manganites is explained.
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  • Hideya Onodera, Hiroki Yamauchi, Yasuo Yamaguchi
    1999 Volume 68 Issue 8 Pages 2526-2529
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Magnetic properties of the single-crystalline tetragonal HoB2C2 compound were investigated. An antiferromagnetic transition occurs at 5.8 K. At 5.0 K, a spin-reorientation transition of the first order occurs, and spontaneous magnetizations appear along the a- and [1~1~0]-axes. Magnetization processes below 5.0 K are well scaled down from those of the antiferroquadrupolar ordering compound DyB2C2 and are well interpreted by postulating the magnetic structure similar to that of DyB2C2. The phase below 5.0 K is the one with competitive coexistence of the antiferromagnetic and antiferroquadrupolar order. The result implies that the antiferroquadrupolar ordering transition occurs below the antiferromagnetic transition temperature and that a pure antiferroquadrupolar ordered phase only in the magnetic fields exists along the [1~1~0]-axis.
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  • Manabu Takahashi, Jun–ichi Igarashi, Peter Fulde
    1999 Volume 68 Issue 8 Pages 2530-2533
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We calculate the anomalous X-ray scattering (AXS) intensity for LaMnO3 using the band calculation based on the local density approximation. We use the dipole approximation for the K-edge absorption process on Mn sites. We show that the Jahn-Teller distortion gives rise to large AXS intensities through the modification of the 4p states of Mn via the oxygen potential on the neighboring sites. We show that the effect of the anisotropic part of the d-p Coulomb interaction on Mn sites is negligible for the AXS intensity. We also show that the AXS intensity is extremely insensitive to the magnetic order and that it increases roughly in proportion to the square of the magnitude of the local distortion.
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  • Jun–ichi Inoue, Akira Shimizu
    1999 Volume 68 Issue 8 Pages 2534-2537
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We propose a new method of calculating nonlinear optical responses of interacting electronic systems. In this method, the total Hamiltonian (system+system-pump interaction) is transformed into a different form that (apparently) does not have a system-pump interaction. The transformed Hamiltonian, which we call the pump built-in Hamiltonian, has parameters that depend on the strength of the pump beam. Using the pump built-in Hamiltonian, we can calculate nonlinear responses (responses to probe beams as a function of the pump beam) by applying the linear response theory. We demonstrate the basic idea of this new method by applying it to a one-dimensional, two-band model, in the case where the pump excitation is virtual (coherent excitation). We find that the exponent of the Fermi edge singularity varies with the pump intensity.
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  • Ki–ichi Yamamoto, Tsuyoshi Kimura, Tadahiko Ishikawa, Takuro Kat ...
    1999 Volume 68 Issue 8 Pages 2538-2541
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Raman spectra have been investigated for a single crystal of La1.2Sr1.8Mn2O7 that shows colossal magnetoresistance around the Curie temperature TC = 126 K. Several broad phonon peaks grow with decrease of temperature down to TC but disappear below TC, which can be clearly ascribed to a change in the charge/orbital correlation by comparison with the spectra for the charge/orbital ordered states of the layered manganites (La0.5Sr1.5MnO4 and LaSr2Mn2O7). Such a real-space charge density fluctuation is also observed to cause the low-energy diffuse Raman response, the B1g component of which is critically suppressed below TC as well.
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  • Miki Wadati
    1999 Volume 68 Issue 8 Pages 2543-2546
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Quantum mechanics of the free fall is studied. The general solution of the Schrödinger equation is obtained by way of the momentum representation. The initial value problem is explicitly solved. Further, its relations to the macroscopic wavefunctions and the hydrodynamic equations are discussed.
  • Hiroaki Onishi, Masamichi Nishino, Naoki Kawashima, Seiji Miyashita
    1999 Volume 68 Issue 8 Pages 2547-2552
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    A quantum Monte Carlo method combining update of the loop algorithm with the global flip of the world line is proposed as an efficient method for studying the magnetization process in an external field, which has been difficult because of inefficiency of the update of the total magnetization. The method is demonstrated in the one dimensional antiferromagnetic Heisenberg model and the trimer model. We attempted various other Monte Carlo algorithms to study systems in the external field and compared their efficiency.
  • Shinya Kizaki, Makoto Katori
    1999 Volume 68 Issue 8 Pages 2553-2560
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Canopy is the uppermost branchy layer of trees and spatial distribution of canopy gaps is important for the coexistence of species and the forest dynamics. A new method to analyze the canopy-gap structure is proposed, in which configurations of canopy-gap sites are approximated by the Ising-Gibbs states with two parameters. Results of the application to the real data of a neotropical forest in Barro Colorado Island, Panama, and of a deciduous forest in Ogawa Forest Reserve, Japan, show the validity of our method. Canopy-gap structures of the forests are not exactly critical but nearly critical and the scaling argument of the Ising spin configurations is useful to explain the power-law distributions of gap sizes reported by ecologists.
  • Nobuhiro Yamanaka
    1999 Volume 68 Issue 8 Pages 2561-2569
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Hyperfine structure constants are precisely calculated for the 1s22s~2S1/2 and 1s22p~2P1/2, 3/2 states of the 7Li atom and the 9Be+ ion. To describe accurately the core polarization, which is important for the hyperfine structure, wave functions are generated with a large-scale multiconfigurational Hartree-Fock method. Corrections due to the finite nuclear mass and size, the relativistic effect, and the quantum electrodynamics (QED) effect are considered. The effect of the finite nuclear size includes that of the nuclear magnetization structure (Bohr-Weisskopf effect). The corrected values of the magnetic dipole and the electric quadrupole hyperfine structure constants of 7Li are determined to be A1/2=401.7033(790) MHz for the 2S1/2 state, and A1/2=45.98429(715) MHz, A3/2=-3.13482(55) MHz, and B3/2=-0.208395(10) MHz for the 2P1/2, 3/2 states. The corresponding values for 9Be+ are A1/2=-625.0608(1720) MHz, and A1/2=-117.9819(247) MHz, A3/2=-0.9381(18) MHz, and B3/2=2.26490(14) MHz. The present result shows a satisfactory agreement with experiments.
  • Hajime Tanuma, Joseph Sanderson, Nobuo Kobayashi
    1999 Volume 68 Issue 8 Pages 2570-2575
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Helium cluster ions have been observed when diatomic molecular ions, N2+, CO+, and O2+, are injected into a drift tube filled with helium gas cooled by liquid helium. The structures of cluster ions and three-body association rates have been discussed. Each size distribution of cluster ions XHen+ (X = N2, CO, and O2, n ≤ 13) in mass spectra strongly depends on the electric field strength in the drift tube. A common magic number n = 12 is observed for these three clusters, which corresponds to the icosahedral structure. Another magic number n = 2 is observed only for O2Hen+, which is similar to O2Ar2+ reported as a very stable cluster ion. For each injected ion with helium atoms, the rate coefficients at 4.4 K are estimated roughly by the extrapolation method.
  • Masakazu Tajima, Takashi Yabe
    1999 Volume 68 Issue 8 Pages 2576-2584
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Impact of a vessel on water surface is simulated by the CIP (Cubic-Interpolated Pseudoparticle/ Propagation) scheme. The simulation demonstrates that air layer between vessel and water surface plays an important role to determine the pressure profile. In particular at small attack angle (or dead-rise angle), air flow along this layer between vessel and water gains speed sufficient to induce the Kelvin-Helmholtz instability which leads to a water wave of small wavelength. Because of this air layer, the maximum pressure is largely reduced at the small attack angle compared with Wagner's theory and becomes much closer to Chuang's experiment.
  • Tsuguo Takahashi
    1999 Volume 68 Issue 8 Pages 2585-2591
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The secondary flow around an oscillating circular cylinder in a uniform flow is investigated with the successive approximation of the Navier-Stokes equation for low Reynolds numbers. The approximation is based on the Oseen's one and the equation and the solution are expanded in the power series of the Reynolds number. It is shown that the secondary flow is obtained in the order of the square of the Reynolds number and directs to the upstream for low frequencies of the oscillation. The drag due to the secondary flow is expressed in the velocity and the oscillation amplitudes and takes positive values for low values of the Reynolds numbers and the frequencies.
  • Takeshi Miyazaki, Koki Ueno, Tomoyuki Shimonishi
    1999 Volume 68 Issue 8 Pages 2592-2601
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Vortex motions in a stably stratified rotating fluid are considered theoretically, based on the quasigeostrophic approximation. A class of exact solution is obtained, which represents a tilted spheroidal volume with uniform potential vorticity embedded in an otherwise quiescent fluid of infinite extent. The spheroid rotates steadily about the vertical axis, where the angular velocity is independent of the inclination angle of the axis of symmetry from the vertical axis. We study the stability of these solutions against infinitesimal disturbances. Highly elongated prolate spheroids are shown to be unstable if the inclination angle is large. In contrast, oblate spheroids of certain aspect ratio are unstable even if the inclination angle is very small. This instability is caused by resonace between the tilted rotation and other disturbance modes.
  • Kohji Yamamoto, Nobuaki Ikuta
    1999 Volume 68 Issue 8 Pages 2602-2610
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Electron transport properties near negative differential conductivity (NDC) region are investigated using Monte-Carlo simulation. The excitation collisions that frequently occur within a narrow range of reduced electric field give a remarkable enhancement of the drift velocity, and the NDC is observed in the higher field range with the decrease of the drift velocity back to normal. NDC is merely a side effect of the drift velocity enhancement but cannot be seen in itself. The effects of elastic and inelastic anisotropic scatterings on the electron transport properties are also examined.
  • Sanae–I. Itoh, Kimitaka Itoh
    1999 Volume 68 Issue 8 Pages 2611-2625
    Published: August 01, 1999
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    A statistical mechanics description is extended for a self-sustained inhomogeneous turbulence, including the effects of thermal fluctuations. Interchange mode in the presence of inhomogeneous magnetic field, which reveals a subcritically-excited strong turbulence, is considered as a collective mode. A Langevin equation is formulated for a test mode, in which the coherent interactions with thermal fluctuations are kept as a collisional drag and the incoherent ones are considered to be thermal noise: The coherent nonlinear interactions are kept as a renormalized turbulent drag, and the incoherent ones are considered to be a random self-noise. Both thermal and turbulent excitations are thus included. The solutions of stationary turbulent state are obtained, provided that both noises are statistically independent. The analysis for the fluctuation level, decorrelation rate, and the correlation functions clearly shows the connection between a mode which is excited by thermal fluctuations and the one being subcritically self-excited. The level is expressed as nonlinear functions (with hysteresis) of nonequilibrium parameter (gradient). A phase diagram is obtained in the gradient-temperature space. An application of the extended fluctuation-dissipation theorem for far non-equilibrium system is explicitly made and new statistical relations are presented.
  • Ryo Sugihara, Hideyasu Shamoto
    1999 Volume 68 Issue 8 Pages 2626-2636
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Theoretically determined are the field and the profile of the laser in the anisotropic plasma. The beam profile referring to the beam in vacuum is explicitly settled down by solving a boundary value problem. This is also done for the reflected wave. The use of a Gauss-type general solution to the Helmholtz equation governing the beam is intensively made. A different Rayleigh range for each wave propagating parallel to the magnetic field B0 is explicitly obtained. Also explicitly determined are two Rayleigh ranges which coexist when a wave propagates perpendicular to B0 and which specify the major and the minor axes of the elliptical cross section of the beam. Extraordinary wave is shown to be anomalously reflected at the boundary.
  • Tatsuhiro Yogi
    1999 Volume 68 Issue 8 Pages 2637-2641
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The evidence of the existence of dimer (HF)2 in liquid state are obtained by the conditional probability density function and the average of angle between two molecular axes by this c.p.d.f. in molecular dynamics simulation. The most observable state in dimer (HF)2 is in a more stable state with the bending angle θ=62.9°, d(HF)=1.748 A, d(FF)=2.505 A and d(HH)=2.226 A at 300 K and the least observable state in dimer (HF)2 is in an intermediate state with the bending angle θ=111.5°, d(HF)=1.717 A, d(FF)=2.489 A and d(HH)=2.027 A at 300 K. These values are in fairly good agreement with X-ray and electron diffraction experiments. These values at 200 K are also described in this paper. No evidence has been found of the formation of rings.
  • Atsushi Mori
    1999 Volume 68 Issue 8 Pages 2642-2647
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Some details of a recent development [A. Mori et~al.: J. Phys. Soc. Jpn. 63 (1994) 1635] of a molecular theoretical formulation [H. Nakano: J. Phys. Soc. Jpn. 56 (1987) 641] of the theory of the crystal-melt interface are reported. Further, the interfacial tension and the boundary between the activation- and the activationless-growth regimes are investigated.
  • Hiroshi Abe, Yoshie Matsuo, Ken–ichi Ohshima
    1999 Volume 68 Issue 8 Pages 2648-2653
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The effect of atomic vacancies relating to martensitic phase transition in an Au-47.5 at.%Cd-0.75 at.%Cu alloy has been investigated with changing thermal treatments by X-ray diffraction method. In a quenched sample, the diffuse scattering is observed around q = 3/4[110]*, 1/3[11 = 2 ]* and 2/3[11 = 2 ]* and their equivalent positions, though it is not seen at 1/4[110]*. This origin of diffuse scattering is considered as the strain field around vacancies, since it disappears with annealing at 473 K. In addition, the diffuse peaks at q = 1/3[1 = 1 0]* derived from TA2 [1 = 1 0] phonon mode are seen both in a quenched and a slow-cooled samples at room temperature. 1/3[1 = 1 0]*-diffuse intensities of a quenched sample gradually increase close to transition temperature ( M s=260 K) due to phonon softening. On the other hand, in a slow-cooled sample, the diffuse peaks at 1/3[1 = 1 0]* are decreasing with decreasing temperature. However, in a slow-cooled sample, time dependence of diffraction peak profile for 220β 2 Bragg reflection is observed during the isothermal holding above M s. Therefore, atomic vacancies are very sensitive to the mechanism of martensitic phase transition.
  • Masashi Watanabe, Yoshio Nogami, Kokichi Oshima, Hatsumi Mori, Shoji T ...
    1999 Volume 68 Issue 8 Pages 2654-2663
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    A band structure calculation based on the X-ray structure analysis reveals that pressure raises quasi one-dimensionality of the Fermi surface of the title compound. A 2kF lattice modulation is observed with a wave vector q3 =(2/3~0~0.29) at 10.7 kbar and room temperature. This is the first observation of pressure-induced CDW. With cooling, the wave vector of the modulation changes from q3 to commensurate q3 =(2/3~0~1/3) below 240 K. On the other hand, at ambient pressure and 20 K where the resistivity begins to increase rapidly, three-dimensional short range ordering occurs for the weak diffuse spot with a wave vector q2 =(0~0~1/2). This modulation is ascribable to an occurrence of charge ordering possibly caused by the nearest neighbor Coulomb interaction V. A schematic phase diagram for the electronic state is presented.
  • Toshiaki Ohsaka, Tadanobu Shoji
    1999 Volume 68 Issue 8 Pages 2664-2668
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    To clarify the OH effect on low-frequency modes, the far-infrared absorption of silica glass containing --800 wt. ppm of OH has been newly measured in the region 10--100 cm-1 at room temperature, and quantitatively compared with that of silica glasses with different OH concentrations. OH-related absorption changes showed a monotonic increase with frequency and broad peaks corresponding to the boson peak shifted to lower frequencies with OH content. It is considered that OH ions which enter silica glass by breaking Si---O bonds, change sizes of clusters constructing a glass network structure and consequently contribute to the far-infrared absorption increase. From the above OH effect, the boson peak is suggested to be due to collective motions of atoms closely related to the clusters.
  • Takahiro Koishi, Masakatsu Misawa
    1999 Volume 68 Issue 8 Pages 2669-2672
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Molecular dynamics simulation was carried out for B2O3-Na2O melt by using the modeled pair potential. The total pair distribution function derived was in good agreement with the experimental result. The structural units such as four- or three-coordinated B atoms and their life times were analyzed to characterize the network structure of melt. It was found the life time of four-coordinated B atom was very short. We also simulated the viscosity of the melt and discussed the relation of the viscosity and network structure.
  • Isao Hashiguchi, Yoshihiro Kuroiwa, Akikatsu Sawada
    1999 Volume 68 Issue 8 Pages 2673-2678
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The orthorhombic to monoclinic phase transition in CsLiCrO4 crystal has been studied with X-ray diffraction to clarify the mechanism of the phase transition. Temperature dependence of lattice constants a, b, c, γ and integrated intensity of Bragg reflections (h0l) has been measured. The experimental results are analyzed on the basis of two-sublattice ferrielastic model. It has been found that CsLiCrO4 crystal has two kinds of sublattice order parameters with a fast-ordering component q1 and a slow-ordering component q2. The former is associated with ordering of CrO4 sublattice, while the latter with ordering of Cs sublattice. CsLiCrO4 crystal is the first ferrielastics which has been proved from microscopic point of view to consist of two kinds of sublattice strains with opposite signs and different magnitudes.
  • Hirotake Shigematsu, Masato Kubota, Masakazu Nishi, Hiroyuki Mashiyama ...
    1999 Volume 68 Issue 8 Pages 2679-2683
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The effect of hydrostatic pressure on the low-temperature structural phase transitions in Rb2ZnBr4 has been investigated by the use of neutron scattering technique. The phase III-to-IV transition temperature, T3=112 K at atmospheric pressure, increased by applying pressure with a rate of 7 K/kbar. The phase IV-to-V transition temperature, T4=76 K at atmospheric pressure, decreased by applying pressure with a rate of -45 K/kbar. At high pressure, two high-order pseudo-commensurate phases characterized by wave vectors qz ~= frac 3 11 and frac 4 15 were observed in addition to the already known commensurate ones of qz= frac 2 7 and ¼. The space group of the commensurate phase of qz=¼ under high pressure was suggested to be P21/c11 from the extinction rule.
  • Masahito Hashimoto, Masako Takasu
    1999 Volume 68 Issue 8 Pages 2684-2691
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We study the superfluid-insulator transition of the 2-D boson system on random surfaces. Using quantum Monte Carlo simulation and grand-canonical ensemble, we investigate the random Hubbard model and study the phase transition between the superfluid phase and the Bose glass insulator phase. Changing the chemical potential μ, we observe the transition from the superfluid phase to the insulator phase. We show the dimensional dependence of the transition by comparing the results of 2-D and 1-D boson systems. To study the localization of the boson paths, we perform the simulation on the anisotropic surfaces, and discuss the crossover from 2-D system to 1-D system.
  • Kazunari Kususe, Yuzo Hori, Shugo Suzuki, Kenji Nakao
    1999 Volume 68 Issue 8 Pages 2692-2696
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    We have theoretically studied the geometries and electronic structures of solid oxygen under high pressures. The calculations were performed by using a first-principles method based on the density-functional theory combined with a scissors method to correct the energy gap appropriately. We found that the molecular dissociation does not occur at the metallization pressure. Furthermore, we found that spin polarization is largely decreased by the application of pressure and almost disappears at the metallization pressure.
  • Kunihiko Maezawa, Satoshi Akamaru, Tomohiko Kuwai, Yosikazu Isikawa, J ...
    1999 Volume 68 Issue 8 Pages 2697-2702
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Magnetoresistance and de Haas-van Alphen measurements have been performed to investigate the Fermi-surface property of LaNi2Al5, which is a reference material of the magnetic dense-Kondo compound CeNi2Al5. Thirteen branches with the frequencies from 1.25 × 106 to 101 × 106 Oe have been observed in the angular-resolved dHvA measurements, and the magnetoresistance shows the existence of open orbits. The results are well explained by the Fermi surfaces obtained from an FLAPW band-structure calculation.
  • Chisa Hotta
    1999 Volume 68 Issue 8 Pages 2703-2714
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The ground states of π-d system (DCNQI)2Cu is studied theoretically based on the mean-field calculation with the 6-chain periodic Anderson model by extending the 3-chain model introduced earlier [J. Phys. Soc. Jpn. 68 (1999) 941]. Prediction is made for the spatial pattern of charge density modulations on DCNQI chains in the insulating phase with the 3-fold periodicity, together with the characteristic features of the magnetic states under higher pressure. The successive phase transitions in accordance with the upshift of the Cu d-level of this 6-chain model are similar to those of the 3-chain model.
  • Yoshikata Tobita, Hiroshi Kamimura
    1999 Volume 68 Issue 8 Pages 2715-2720
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    In this paper we investigate the multiplet structure of a single CuO5 pyramid embedded in Bi2Sr2CaCu2O8+δ (Bi2212) for an insulating phase of δ=0 and a superconducting phase of δ=0 with Tc= 85 K. In this study, we use the multi-configuration self-consistent field variational method with configuration interaction to calculate the lowest states of the Zhang-Rice spin-singlet (1A1) and Hund's coupling spin-triplet (3B1) as accurate as possible. In the case of δ=0 we find that the 1A1 state is the lowest. It is lower than the 3B1 state by 2.15 eV. On the other hand, in the case of δ=0.25 we find that the 1A1 and the 3B1 multiplets are very close in energy, and mixed easily by transfer interaction between clusters. In the case of δ=0.25, we show that a coherent state for a dopant hole is composed in such a way that the 1A1 and the 3B1 multiplets appear alternately when the localized spin form local antiferromagnetic ordering in a region of the spin-correlation length.
  • Takuya Okabe
    1999 Volume 68 Issue 8 Pages 2721-2728
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    To investigate the low temperature resistivity R=AT2 due to quasiparticle-quasiparticle scattering of Fermi liquids, we numerically solve the linearized transport equation. It is shown that the conventional approximation to neglect the momentum dependence of the transport relaxation time τp is quantitatively satisfying, except in the vicinity of the threshold at which the resistivity vanishes. After discussing the many-band model in general terms, we study a solvable case of a two-band model in order to verify that each band carries a comparable amount of current, regardless of the difference in the effective mass of the quasiparticle in each band.
  • Jun–ichiro Ohe, Kousuke Yakubo
    1999 Volume 68 Issue 8 Pages 2729-2734
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Using a novel transfer matrix method, photon-assisted quantum transport through a quantum point contact (QPC) has been studied theoretically. Although the previous WKB theory predicts a ministep structure in the conductance of an irradiated QPC, negative experimental evidence has been reported so far. Our numerical results for a two-dimensional QPC model with realistic parameters suggest that (i) clear ministeps can be expected if the radiation field is several times stronger than that in experiments, (ii) in contrast to the WKB prediction, only ministeps in the emission side will be observed, and (iii) a wavefunction modulation by a static potential plays an important role in photon-assisted quantum transport, which has not been properly evaluated in the previous theory. We also insist that a simple scenario based on the Tien-Gordon picture does not describe correctly the ministep structure.
  • Hiroyuki Yamada, Yutaka Ueda
    1999 Volume 68 Issue 8 Pages 2735-2740
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Physical properties of β-AxV2O5 (A=Na, Ag) have been systematically reconsidered from structural, electric, and magnetic points of view. We prepared samples, both powder and single crystal, with precise composition for this purpose. The single crystals have been successfully grown by a self flux method using NaV3O8 as a flux. The precise adjustment of x was performed by embedding the as-grown crystals in a large amount of powder and heating them. β-Na0.33V2O5 was not a conventional semiconductor but a possible anisotropic metal at higher temperatures. It exhibited a metal-insulator transition at 136 K, suggesting a charge ordering. The ordered structure underwent a magnetic ordering with Tc= 24 K. We also observed a development of 1× 2× 1 superstructure below 230 K, suggesting an ordering of the intercalated ion. Those transitions similarly occurred in β-Ag0.33V2O5. The deviation from x = 0.33 drastically decreased the transition temperatures or magnitudes of anomalies at the transitions, and both metallic behavior in the high temperature phase and magnetic ordering were lost.
  • Akihiko Nishida, Chihiro Taka, Kazumi Horai
    1999 Volume 68 Issue 8 Pages 2741-2749
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Inhomogeneous ESR broadening due to local field variation was studied in the superconducting YBa2Cu3O7- δ . The change in the ESR lineshape was observed for a paramagnetic “spin probe” applied on one surface of the pellet sample. The ESR line just below Tc exhibited tendency of asymmetric broadening. However, upon further cooling, the lineshape evolved into double peak structure. The obtained ESR profiles were analyzed with the assumption that respective peaks correspond to two different spin sites with the aid of computer lineshape calculations. The linewidths for both sites increased linearly with temperature below Tc. On the other hand, the resonance fields varied with temperature very differently for each site, inferring difference in superconductivity for different spin positions. Mechanisms for the observed ESR variations were discussed along with some crossover points such as superconducting transition or irreversibility temperatures. Electron microscopic observations were also carried out for examining possible origins of the superconducting inhomogeneity.
  • Yoshihisa Obi, Manabu Ikebe, Hitoshi Wakou, Hiroyasu Fujimori
    1999 Volume 68 Issue 8 Pages 2750-2754
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The transition temperature Tc, parallel (Hc2//) and perpendicular (Hc2⊥) critical fields and magnetic properties have been investigated for Nb(400 Å)Co(X Å) and V(400 Å)/Co(X Å) superconductor/ferromagnet multilayers. Tc rapidly decreases with increasing Co layer thickness (dCo) up to the threshold values, dc-- 12 Å for Nb/Co, and dc-- 24 Å for V/Co. With further increase of dCo, Tc remains almost constant. The dCo dependence of Tc is closely correlated with dimensionality of superconductivity, i.e., the superconductivity is quasi-two-dimensional (quasi-2D) below dc with finite interlayer coupling, and it becomes decoupled 2D above dc. For both multilayer systems a spontaneous magnetization has been observed for dCo>~ 8 Å at 10 K.
  • Shigenobu Sakita, Fumihiko Nakamura, Takashi Suzuki, Toshizo Fujita
    1999 Volume 68 Issue 8 Pages 2755-2761
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    In order to clarify the influence of lattice deformation on the electronic states, we have measured ultrasound velocity and X-ray diffraction of La2- x- yNd_ ySr_ xCuO4 (LNSCO) with a particular carrier number of p -- 1/8. As temperature is reduced, LNSCO exhibits a first-order transition to the low-temperature tetragonal phase P42/ncm, after a second-order transition from the well-known orthorhombic phase Bmab to another orthorhombic phase Pccn. A semiconductor-like upturn is observed in resistivity, indicating tendency of localization in the normal state in these low-temperature phases of Pccn and P42/ncm. These structural changes are also reflected on the magnetic properties, which are well understood only with taking into consideration the antiferromagnetic coupling between Nd and Cu spins.
  • Shigeki Onoda, Masatoshi Imada
    1999 Volume 68 Issue 8 Pages 2762-2772
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    Pseudogap phenomena of high-Tc cuprates are examined. In terms of AFM (antiferromagnetic) and dSC (dx2-y2-wave superconducting) auxiliary fields introduced to integrate out the fermions, the effective action for 2D electron systems with AFM and dSC fluctuations is considered. By the self-consistent renormalization (SCR), the NMR relaxation rate T1-1, the spin correlation length ξ_σ and the pairing correlation length ξd are calculated. From this calculation, a mechanism of the pseudogap formation emerges as the region of dominant d-wave short-range order (SRO) over AFM-SRO. When damping for the AFM fluctuation strongly depends on the dSC correlation length through the formation of precursor singlets around (π, 0) and (0, π) points in the momentum space, the pseudogap appears in a region of the normal state characterized by decreasing 1/T1T and increasing AFM correlation length with decrease in temperature. This reproduces a characteristic feature of the pseudogap phenomena in many underdoped cuprates. When the damping becomes insensitive to the dSC correlation length, the pseudogap region shrinks as in the overdoped cuprates.
  • Chitoshi Yasuda, Akihide Oguchi
    1999 Volume 68 Issue 8 Pages 2773-2778
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The spin-wave theory and the coherent potential approximation are applied to a spin S Heisenberg antiferromagnet with nonmagnetic impurities on square lattice. The impurity effects are taken into account by substituting S(1-x) for S and using the coherent potential approximation to the exchange interaction, where x is the impurity concentration. At T=0 for S=1/2 the critical impurity concentration xc of the Néel state is 0.303 and the percolation threshold xp is 0.500. The ground state in xcp is the disordered state with the spin gap. For S ≥q 1 the long range Néel order vanishes at xp=0.500. These results explain qualitatively the experimental results of La2Cu1-xMgxO4 (S=1/2) and K2Mn1-xMgxF4 (S=5/2). The difference of xc between these materials is caused by the decrease in the magnitude of the effective spin with impurity doping. The spin gap is expected to be observed for La2Cu1-xMgxO4 in xcp at low temperatures.
  • Wei Chen, Kazuo Hida
    1999 Volume 68 Issue 8 Pages 2779-2782
    Published: August 01, 1999
    Released on J-STAGE: June 28, 2000
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    The one dimensional S=1/2 XXZ model with dimerization (1-j) and quadrumerization δ is studied by the numerical exact diagonalization of finite size systems. Using the conformal field theory and the level spectroscopy method, we calculate the ground state phase diagram with XY-like anisotropy Δ (0<Δ<1). The ground states of this model contain the Haldane state, S=1 dimer state, S=1 large- D state and S=1/2 dimer state as limiting cases. The Δ and δ-dependence of the critical exponent ν of the energy gap is determined from the conformal dimensions of excited states.
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