Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 69, Issue 2
Displaying 1-47 of 47 articles from this issue
  • Naoaki Bekki
    2000 Volume 69 Issue 2 Pages 295-298
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    In order to show that some periodic orbits of a fifth-order system of magnetoconvection are embedded in a three-dimensional subspace, main projections onto a three-dimensional subspace from the five-dimensional space are numerically investigated. It is found that the periodic orbits are topologically equivalent to a (p, q)-torus knot, where its curve closes after rotating q times in the meridional direction and p times in the longitudinal direction. In terms of a braid word for the torus knot, a (2, 7)-torus knot is finally obtained in the fifth-order system through the complicated bifurcations under parameter variation. This suggests that topological invariants embedded in a three-manifold can be extracted from realistic dissipative higher dimensional dynamical systems.
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  • Hajime Tanaka
    2000 Volume 69 Issue 2 Pages 299-302
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We propose a phenomenological model of mechanical instability in a polymer melt having a nonmonotonic constitutive law. It relies on the fact that a nonmonotonic constitutive law is a result of shear-induced orientational ordering of polymers and this orientational order parameter has a common symmetry with that of liquid crystal. Our model shows that there exists gradient energy of “purely mechanical origin” associated with shear-rate inhomogeneity. We derive a “nonlocal” phenomenological equation describing shear banding, which is similar to the Cahn-Hilliard equation. The analogy of inhomogenization of flow fields to phase separation is discussed.
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  • Masaaki Matsukuma, Kenta Kaimoto, Yoshinobu Kawai
    2000 Volume 69 Issue 2 Pages 303-305
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    By setting a mesh grid as a boundary condition in the ion-beam-plasma system, we attempted to observe chaotic behavior caused by the ion-ion instability. In the presence of the mesh grid the ion-ion instability showed chaotic behavior. The estimated correlation dimension was a noninteger value larger than 3. Furthermore, the spatial energy distribution of ions was measured two dimensionally with an energy analyzer, suggesting that the present system is one dimensional.
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  • Hee–Tae Jeong, Se–Young Jeong, W. T. Kim, D. H. Kim
    2000 Volume 69 Issue 2 Pages 306-308
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    In order to verify the existence of fourfold ferroelastic domain wall, which is suggested by group-theoretical consideration, polarizing microscopy and X-ray Laue photography experiments were carried out for BiVO4 crystal which is expected to have fourfold walls only. The experimental results showed that the domains in ferroelastic BiVO4 have fourfold rotational symmetry relationship and the domain walls are characterized by these fourfold symmetry elements. This proves the domain walls in BiVO4 to be the fourfold wall and they were indexed as (101) and ( bar 1 01) in monoclinic reference system.
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  • Cheng Yuanfa, Jiang Bi Bo
    2000 Volume 69 Issue 2 Pages 309-311
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The motion of a kink soliton in hydrogen bonded chains in the presence of an external force and damping is discussed, influence of the motion and the optical mode of the heavy-ion sublattice on the proton sublattice is investigated, based on the two-component soliton model. The solution, the mobility and the conductivity of a kink soliton are found. The calculated results are in good agreement with the experimental results.
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  • Shigeki Onoda, Masatoshi Imada
    2000 Volume 69 Issue 2 Pages 312-315
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We investigate pseudogap phenomena in the 2D electron system. Based on the mode-mode coupling theory of antiferromagnetic (AFM) and dx2-y2-wave superconducting (dSC) fluctuations, single-particle dynamics is analyzed. For the parameter values of underdoped cuprates, pseudogap structure grows in the single-particle spectral weight A(k, ω) around the wave vector (π, 0) and (0, π) below the spin pseudogap temperature TPG signaled by the reduction of dynamical spin correlations in qualitative agreement with the experimental data. The calculated results on A(k, ω) for the overdoped cuprates also reproduce the absence of the pseudogap in the experiments. We also discuss limitations of our mode-mode coupling approach.
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  • Kikuo Harigaya
    2000 Volume 69 Issue 2 Pages 316-319
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Magnetic impurity effects on metallic carbon nanotubes are studied theoretically. The resolvent method for the multichannel Kondo effect is applied to the band structure of the k · p perturbation hamiltonian. The local non-Fermi liquid behavior is realized at temperatures lower than the Kondo temperature TK. The density of states of the localized electron has a singularity -- |ω|1/2 which gives rise to a pseudo gap at the Kondo resonance in low temperatures. The temperature dependence of the electronic resistivity is predicted as T1/2, and the imaginary part of dynamical susceptibilities has the |ω|1/2 dependence. Possible experimental observations are discussed.
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  • Toshifumi Itakura, Yoshikazu Suzumura
    2000 Volume 69 Issue 2 Pages 320-323
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The interplay of alternating potential and dimerization (u) has been examined for the spin density wave (SDW) state in a quasi-one-dimensional system at quarter-filling, which is expressed in terms of θ, a phase of the SDW. By taking account of the dimerization energy u2 /(2g) with an effective coupling constant g, we evaluate critical temperatures, Tc, Ts and Tu, corresponding to the onset of Δc (∝ ‹ cos θ › ), Δs (∝ ‹ sin θ › ) and u, respectively. Two kinds of noticeable critical temperatures of the SDW states are obtained where Tc > Ts = Tu for g < gc and Tu > Tc = Ts for g > gc. The quantity gc is increased by both the alternating potential and the interchain coupling. The relevance to the SDW state in (EDT-TTF)2AuBr2 salt is discussed.
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  • Kazunori Aoki
    2000 Volume 69 Issue 2 Pages 324-327
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Time-resolved spatial structures of a current density filament in n-GaAs have been investigated under a dc+ac drive voltage Vdc+Vacsin 2π fdt at 4.2 K. With a sinusoidal drive of Vdc=0.95 V, Vac=388 mV and fd=100 kHz, we observe an S-shaped I-V curve caused by the impact ionization avalanche of neutral shallow donors and subsequent formation of a current density filament. Evolution of the current-density filament was studied by the time-resolved measurements of the photoluminescence quench-patterns. A new finding is the Turing bifurcation observed at around the breakdown voltage.
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  • Yositake Takane, Yasusi Koyama
    2000 Volume 69 Issue 2 Pages 328-331
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We study the weak-localization (WL) effect in mesoscopic wires of ferromagnetic metals, focusing on the decoherence caused by a magnetic domain wall (DW). The decoherence leads to suppression of the WL correction to conductance. A real-space approach is presented to describe the WL effect which explicitly takes into account the location of a DW. If the length L of a wire is much smaller than the phase coherence length Lφ, the WL correction is shown to depend on the location of the DW. In the opposite limit of L >> Lφ >> W (W: thickness of the DW), it is shown that the DW reduces the WL correction by a factor of (1-W/2L) compared with that in the absence of the DW. The influence of the DW on the amplitude of the Altshuler-Aronov-Spivak oscillation in a metallic ring partially replaced by a ferromagnetic wire is also discussed.
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  • Hiroyuki Yamase, Hiroshi Kohno
    2000 Volume 69 Issue 2 Pages 332-335
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    To reconcile the two experimental findings on La2-xSrxCuO4, namely, Fermi surface (FS) observed by angle-resolved photoemission spectroscopy and sharp incommensurate magnetic peaks by neutron scattering, we propose a picture that a quasi-one-dimensional FS (q-1dFS) is realized in each CuO2 plane whose q-1d direction alternates along the c-axis.
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  • Yasumasa Hasegawa, Kazushige Machida, Masa–aki Ozaki
    2000 Volume 69 Issue 2 Pages 336-339
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Several possible odd-parity states are listed group-theoretically and examined in light of recent experiments on Sr2RuO4. These include some of the f-wave pairing states, d(k)∝ z kxky(kx + iky) and z (kx2-ky2)(kx + iky) and other z (kx + iky)cos ckz (c is the c$-axis lattice constant) as the most plausible candidates. These are time-reversal symmetry-broken states and have line nodes running either vertically (the former two) or horizontally (the latter), consistent with experimental results. Characterizations of these states and other possibilities are given.
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  • Mariko Ishii, Hidekazu Tanaka, Mikiko Hori, Hidehiro Uekusa, Yuji Ohas ...
    2000 Volume 69 Issue 2 Pages 340-343
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The magnetic susceptibility and magnetization curves of an S=½ trimer spin chain system Cu3Cl6(H2O)2·2H8C4SO2 have been measured using single crystals and polycrystals. It was found that the ground state at zero-field is a spin singlet with an excitation gap. This result suggests that the translational symmetry of the Hamiltonian is spontaneously broken in the ground state. A model for the ground state is proposed. The magnetization curve measured at 0.08 K for polycrystals shows that the gap closes at Hc ≈ 3.9 T, from which the magnitude of the gap is evaluated as Δ /kB≈5.2 K.
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  • Taksu Cheon, Takaomi Shigehara, Kazuo Takayanagi
    2000 Volume 69 Issue 2 Pages 345-350
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We consider the regularized approximations of the discontinuity-inducing singular zero-range interaction in one-dimensional quantum mechanics. We prove that two known approximations, one in terms of local potential and the other in terms of separable function are equivalent. We further show that the interaction allows the perturbative treatment through the coupling constant renormalization.
  • K. M. Tamizhmani, Wen–Xiu Ma
    2000 Volume 69 Issue 2 Pages 351-361
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    From a given discrete spectral problem we construct Lax operators for hierarchies of isospectral and nonisospectral lattice soliton systems systematically. We also present algebraic structures of the Kac-Moody-Virasoro type (Witt algebra) related to Lax operators. Based on these algebraic structures we get directly an algebra of commuting symmetry and master symmetry vector fields. Three hierarchies of coupled discrete systems of evolution equations are treated in detail.
  • Hidetoshi Konno, Naoshi Yamamoto, Peter S. Lomdahl
    2000 Volume 69 Issue 2 Pages 362-368
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    It is shown that the method of nonlinear transformation (NTR) is a powerful tool for obtaining approximate analytic solutions of nonlinear ordinary differential equations (ODEs). Special attention is paid to the performance of a family of double exponential NTRs. Applications of the double exponential NTRs to some nonlinear third order ODEs in the normal form are given with numerical examples.
  • C. S. Lim, Bungo Taga
    2000 Volume 69 Issue 2 Pages 369-372
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    By an explicit calculation we show that in ordinary SU(5) logarithmic divergence in the amplitude of μ → eγ cancels among diagrams and remaining finite part is suppressed by at least 1/MGUT2. In SUSY SU(5), when the effect of flavour changing wave function renormalization is taken into account such logarithmic correction disappears, provided a condition is met among SUSY breaking masses. In SUGRA-inspired SUSY GUT the remaining logarithmic effect is argued not to be taken as a prediction of the theory.
  • Girish C. Joshi, Hari M. Agrawal
    2000 Volume 69 Issue 2 Pages 373-377
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The fluctuations of the p-wave neutron reduced widths for fifty one nuclei have been analyzed with emphasis on recent measurements by a statistical procedure which is based on the method of maximum likelihood. It is shown that the p-wave neutron reduced widths of even-even nuclei follow single channel Porter Thomas distribution (χ2-distribution with degree of freedom ν =1) for most of the cases where there are no intermediate structure. It is emphasized that the distribution in nuclei other than even-even may differ from a χ2-distribution with one degree of freedom. Possible explanation and significance of this deviation from ν=1 is given.
  • Akihiko Ohsaki, Satoshi Nagasaki, Sei–iti Uramoto, Kazuo Takayan ...
    2000 Volume 69 Issue 2 Pages 378-391
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Present work gives for the first time the formulation of the two-center Coulomb-Born approximation (TCCBA) and presents some calculations for the electron-impact excitations in electron-ion-ion systems. The effect of the third body was relatively small in the cases studied so far. However, if the third body is a bare ion with a charge larger than the target ion, there will be a marked influence of the three-body collisions. Utilizing TCCBA we present the total and partial cross sections of hydrogen-like ions He+(Z=2), and C5+(Z=6) in the hydrogen plasma from the ground states 1s to the excited states 2s and 2p0, 2p_± for the collision energies from 0.4Z2 to 2Z2 a.u.; for the excited states of the target ions, Stark effect is also studied. It is found that the presence of another ion have little effect on the 1s-2s transition and the 2s-2p Stark mixing has a prominent effect.
  • Hideyuki Oka, Katsuya Ishii
    2000 Volume 69 Issue 2 Pages 392-400
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The fully three-dimensional interactions of one or two buoyant drops with a fluid-fluid interface are studied numerically at the moderate Reynolds number and Bond number. This complex interaction process is successfully simulated using the three-dimensional level set approach to deal with the deformable interface and drops. The characteristics of vortex ring generated at the coalescence between the interface and the drop depend upon the viscosity ratio between two fluids, and they have much to do with a jet formation process. In the case of two drops, the motion of the trailing drop is influenced by the deformation of interfaces through the coalescence of the leading drop with its homophase. The behavior of the trailing drop is also classified into two types with respect to the viscosity ratio. These studies show that the investigation in the viewpoint of vorticity is effective on the understanding of the interaction between drops and an interface.
  • Elsayed F. Elshehawey, Ayman M. F. Sobh, Elsayed M. E. Elbarbary
    2000 Volume 69 Issue 2 Pages 401-407
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    In this paper, peristaltic motion of an incompressible non-Newtonian fluid through a porous medium is studied in a two-dimensional uniform channel with a sinusoidal wave using long wave approximation. The problem is formulated and analyzed using a perturbation expansion in terms of a variant of the Weissenberg number. Carreau flow is considered in this study to investigate the influence of porous medium. An analytic forms for axial velocity component and pressure gradient have been obtained. Moreover, the pressure rise and friction force were computed numerically. It has been shown that the pressure rise increases as the permeability decreases. Further, it is noted that both pressure rise and friction force does not depend on permeability parameter at a certain value of flow rate. The results were studied for various values of the physical parameters of interest.
  • Sanae–I. Itoh, Kimitaka Itoh
    2000 Volume 69 Issue 2 Pages 408-426
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    A statistical theory of nonlinear-nonequilibrium plasma state with strongly developed turbulence and with strong inhomogeneity of the system has been developed. A unified theory for both the thermally excited fluctuations and the strongly turbulent fluctuations is presented. With respect to the turbulent fluctuations, the coherent part to a certain test mode is renormalized as the drag to the test mode, and the rest, the incoherent part, is considered to be a random noise. The renormalized operator includes the effect of nonlinear destabilization as well as the decorrelation by turbulent fluctuations. Formulation is presented by deriving an Fokker-Planck equation for the probability distribution function. Equilibrium distribution function of fluctuations is obtained. Transition from the thermal fluctuations, that is governed by the Boltzmann distribution, to the turbulent fluctuation is clarified. The distribution function for the turbulent fluctuation has tail component and the width of which is in the same order as the mean fluctuation level itself. The Lyapunov function is constructed for the strongly turbulent plasma, and it is shown that an approach to a certain equilibrium distribution is assured. The result for the most probable state is expressed in terms of `minimum renormalized dissipation rate', which is given by the ratio of the nonlinear decorrelation rate of fluctuation energy and the random excitation rate which includes both the thermal noise and turbulent self-noise effects. Application is made for example to the current-diffusive interchange mode turbulence in inhomogeneous plasmas. The applicability of this method covers plasma turbulences in much wider circumstance as well as neutral fluid turbulence. This method of analyzing strong turbulence has successfully extended the principles of statistical physics, i.e., Kubo-formula, Prigogine's principle of minimum entropy production rate. The condition for the turbulence transition is analogous to the Maxwell's construction in the phase transition physics in thermodynamical equilibrium. The method provides the extension of the nonequilibrium statistical physics to the far-nonequilibrium states.
  • Sanae–I. Itoh, Kimitaka Itoh
    2000 Volume 69 Issue 2 Pages 427-440
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    A statistical theory of nonlinear-nonequilibrium plasma state with strongly developed turbulence and with strong inhomogeneity of the system has been developed. A Fokker-Planck equation for the probability distribution function of the magnitude of turbulence is deduced. In the statistical description, both the contributions of thermal excitation and turbulence are kept. From the Fokker-Planck equation, the transition probability between the thermal fluctuation and turbulent fluctuation is derived. With respect to the turbulent fluctuations, the coherent part to a certain test mode is renormalized as the drag to the test mode, and the rest, the incoherent part, is considered to be a random noise. The renormalized operator includes the effect of nonlinear destabilization as well as the decorrelation by turbulent fluctuations. The equilibrium distribution function describes the thermal fluctuation, self-sustained turbulence and the hysteresis between them as a function of the plasma gradient. The plasma inhomogeneity is the controlling parameter that governs the turbulence. The formula of transition probability recovers the Arrhenius law in the thermodynamical equilibrium limit. In the presence of self-noise, the transition probability deviates form the exponential law and provides a power law. Application is made to the submarginal interchange mode turbulence, being induced by the turbulent current-diffusivity, in inhomogeneous plasmas. The power law dependence of the transition probability is obtained on the distance between the pressure gradient and the critical gradient for linear instability. Thus a new type of critical exponent is explicitly deduced in the phenomena of subcritical excitation of turbulence. The method provides an extension of the nonequilibrium statistical physics to the far-nonequilibrium states.
  • Fu–qiu Shao, Wang Long, Shao–Bai Zheng
    2000 Volume 69 Issue 2 Pages 441-444
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The electron cyclotron wave current start-up in tokamaks has been simulated using Monte-Carlo method in two-dimensional configuration space (x, y) and two-dimensional velocity space (V//, V). The simulation results of the relationship between start-up current and external vertical magnetic field is consistent with experiments, and the simulation results coincides the physical analyses that the start-up current is obtained by canceling the toroidal drift in one toroidal direction by external vertical magnetic field for energetic electrons in low density plasmas.
  • Heiji Sanuki, Kimitaka Itoh, Masayuki Yokoyama, Akihide Fujisawa, Kats ...
    2000 Volume 69 Issue 2 Pages 445-450
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Theoretical analysis of the electric field bifurcation is made for the LHD plasma. For given shapes of plasma profiles, a region of bifurcation is obtained in a space of the plasma parameters. In this region of plasma parameters, the electric field domain interface is predicted to appear in the plasma column. The reduction of turbulent transport is expected to occur in the vicinity of the interface, inducing internal transport barrier. Within the present simple model, the electric field bifurcation associated with the internal transport barrier is predicted to be realized for the parameter of Te(0)~= 2 keV and n(0)~= 1018(m-3). The boundary of the region of multiple solution is characterized by a scaling Te(0)-- [n(0)]0.4.
  • Naotaka Iwasawa, Akio Ishida, Loren C. Steinhauer
    2000 Volume 69 Issue 2 Pages 451-463
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The ideal magnetohydrodynamic (MHD) stability of static field-reversed configurations is investigated. For the first time, the eigenvector fields and eigenvalues for a variety of global modes are found by applying the Rayleigh-Ritz technique to the variational principle using a verifiably complete basis set. This method is applied to a wide range of equilibria and mode types, including kink and sausage-like modes, modes with intermediate azimuthal mode number, and higher-harmonic modes with respect to the minor radius structure. The findings include the following. Modes with intermediate azimuthal mode number are somewhat more unstable than the well-known tilt mode. The tilt is not stabilized by proper current profile and separatrix shape. The inverse scaling of the tilt growth rate with the elongation (found in previous studies) is not valid in general. This suggests that large elongation alone cannot be relied on for stability when non-MHD corrections are added.
  • Takahiro Sinagawa, Jun Suda, Tsutomu Sato, Hiroaki Saito
    2000 Volume 69 Issue 2 Pages 464-472
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The phonon dispersion carves for PbMoO4 crystal were calculated on the basis of a rigid-ion model. The first-order Raman spectra of Ag mode PbMoO4 crystal were measured in a temperature range from 77 to 473 K. The temperature dependence of the linewidths was analyzed by using the phonon dispersion curves, and the results showed that it was caused approximately by the cubic anharmonic term in crystal potential energy. The temperature dependence of the frequency shift of the Ag mode was analyzed by using the lattice dynamical perturbative treatment. We found that the quartic anharminic term of the first-order perturbation, as well as the cubic term of the second-order one contributes to the temperature dependence of the frequency shift of the Ag mode in the PbMoO4 crystal.
  • Yoshimi Tsuchiya
    2000 Volume 69 Issue 2 Pages 473-478
    Published: February 01, 2000
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    New thermodynamic relations are applied to the liquid Se--Te system to investigate the concentration fluctuations induced by the structural change. The excess Darken stability caused by the structural change has been quantitatively evaluated with experimentally available data. It is definitely negative, and the absolute magnitude of which takes a peak in the composition-temperature region where the structural change occurs. The results provide the thermodynamic basis of the segregation tendency in a microscopic scale developed with increasing temperature, which was found with high resolution neutron diffraction experiments nearly two decades ago. Discussion has been made in relation to the intrinsic instability of chain structure of VIb chalcogenide elements which plays a key role to makes the effective interaction between Se--Te pair dependent on composition and temperature.
  • Ashis Bhattacharjee, Yuji Miyazaki, Michio Sorai
    2000 Volume 69 Issue 2 Pages 479-488
    Published: February 01, 2000
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    Heat capacities of two molecule-based materials NBu4[FeIIFeIII(ox)3] and NBu4[ZnIIFeIII(ox)3] (Bu=n-butyl, ox=oxalate) were measured by adiabatic calorimetery. In case of ferrimagnetic NBu4[FeIIFeIII(ox)3] two phase transitions were detected at 43.3 K (T2) and 217 K (T1) along with a small heat capacity anomaly at 16.3 K (T3). The heat capacity anomaly at 43.3 K is due to the ferrimagnetic ordering, whereas that at 217 K has been assigned to an order-disorder phase transition due to increasing conformational change of the organic cation. The small heat capacity anomaly at T3 seems to arise from a spin glass like state at low temperatures. The enthalpy and entropy gains from the heat capacity anomalies at T1, T2 and T3 are 2.29 kJ mol-1 and 11.47 J K-1 mol-1; 1.37 kJ mol-1 and 22.65 J K-1 mol-1; 0.068 kJ mol-1 and 4.89 J K-1 mol-1, respectively. The sum of the entropies ( = 27.54 J K-1 mol-1) corresponding to the heat capacity anomalies at T2 and T3 is very close to the expected magnetic entropy R ln30 ( = 28.27 J K-1 mol-1) for the spin multiplicity of high spin FeIII and FeII ions. No phase transition around 38 K has been detected, as predicted from previous magnetic measurements. In case of paramagnetic NBu4[ZnIIFeIII(ox)3] a heat capacity anomaly due to a similar order-disorder phase transition was observed at 227 K accompanied with the enthalpy and entropy gains of 2.91 kJ mol-1 and 13.32 J K-1 mol-1, respectively. A model has been applied to realize the high temperature order-disorder phase transition.
  • Norikazu Ishimura, Takao Yamamoto
    2000 Volume 69 Issue 2 Pages 489-496
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Some one-dimensional classical systems with competitive interactions show quite complex ground-state phase-diagrams, in which infinitely many phases exist. A free-surface effect on the ground-state structures of one of such systems is discussed. A direct numerical method is applied to evaluate the ground-state structure of the semi-infinite system. We pay attention to the area near the phase boundary between a non-uniform modulated phase and a uniform phase. The free-surface induces domain-wall structures. The domain-wall may be free from the free surface in some parameter region although it is usually bound near the surface.
  • Makio Uwaha, Katsuhiro Watanabe
    2000 Volume 69 Issue 2 Pages 497-503
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We study the decay process of a small island formed on a facet by numerical integration of a simple model and by theoretical analysis. The relaxation proceeds via surface diffusion without evaporation and impingement of atoms. Steps on the top of the island shrink due to the step tension and a small facet appears. The size of the facet increases as the power of time Rf-- tν, where the exponent ν depends on the initial shape and the rate limiting process. In the kinetics-limited case, step bunching occurs from the bottom and the enlargement of the facet stops at some stage. Analytical expressions for the bunch velocity and the island profile are found.
  • Toshikazu Nakamura, Waka Minagawa, Ryoji Kinami, Toshihiro Takahashi
    2000 Volume 69 Issue 2 Pages 504-509
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    1H-NMR, EPR and static magnetic susceptibility measurements have been performed on an organic conductor, θ-(BEDT-TTF)2CsZn(SCN)4. The 1H-NMR-T1-1 and the spin susceptibility exhibit anomalous enhancements at low temperatures. Around 20 K, where the spin susceptibility shows a minimum, the principal axes of the EPR g-tensor changed their directions, keeping the principal values constant. It indicates a possible change of the electronic nature. The low-temperature electronic state is discussed.
  • Katsurou Hanzawa
    2000 Volume 69 Issue 2 Pages 510-525
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    It is shown that the main origin of the hyperfine field at B nuclei in CeB6 is the transferred hyperfine interaction of the nuclear moment with the electronic spin carried by the electrons in the 2 s and 2 p states of the B ion hybridized with the 4 f states of neighboring Ce ions. The dipole-dipole interaction with the magnetic moments of Ce ions also contributes substantially. In the antiferro-quadrupolar ordering phase II, it is essential to assume the ordering of Γ5-type moments. The reason why the RKKY interaction between the Γ5-type quadrupole moments is strongest is also discussed, on the basis of the estimate of the strength of p-f mixing which plays a vital role in many respects in CeB6.
  • Fumiyuki Ishii, Tamio Oguchi
    2000 Volume 69 Issue 2 Pages 526-531
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    A local-density electronic-band-structure calculation was performed for pyrochlore ruthenium oxides A2Ru2O7 (A = Bi, Tl and Y). As a general feature, these pyrochlores have band structure composed of antibonding states of Ru 4d (t2g) and O 2p orbitals near the Fermi energy (EF) analogous to the layered perovskite superconductor Sr2RuO4. It was found that effects of A ion's orbitals to the band structure near EF are quite important in the pyrochlores. Specifically in Tl2Ru2O7, bands which consist of antibonding states of Tl 6s and O 2p orbitals exist with nearly half-fillings. A tight-binding model shows an energy-gap formation of the Tl-O bands with an orthorhombic lattice distortion. The calculated result suggests importance of coupling between electronic and lattice instabilities, which may be a clue to understand metal-insulator transition observed in Tl2Ru2O7.
  • Shugo Suzuki, Kenji Nakao
    2000 Volume 69 Issue 2 Pages 532-542
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We present a new scalar relativistic formulation for the full-potential linear-combination-of-atomic-orbitals method based on the density-functional theory. Three approximations are introduced to overcome computational difficulty. The first is to consider only the large component of the four-component spinor, neglecting the small component. The second is to neglect the energy dependence in the Hamiltonian reduced for the large component. The third is to replace the material-dependent potential with the atomic potential in relativistic corrections. After the three approximations, we identify the mass-velocity and Darwin terms and also the spin-orbit coupling, where the latter is to be omitted according to the definition of the scalar relativistic formulation. The computational effort of the present method is reduced considerably in comparison with that of the fully relativistic method, being almost the same as that of the nonrelativistic method. We apply the present method within the local-density approximation to several diatomic molecules with heavy elements, crystalline Au, and crystalline InSb. The results are improved considerably in comparison with the nonrelativistic results. The calculated structural properties are in good agreement with the fully relativistic results and also with the experimental results. The calculated electronic properties are also improved considerably in comparison with the nonrelativistic results and are also in good agreement with the fully relativistic results except for the effect due to the spin-orbit coupling.
  • Naoya Tajima, Masafumi Tamura, Yutaka Nishio, Kôji Kajita, Yasuh ...
    2000 Volume 69 Issue 2 Pages 543-551
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We have found quite a new type of transport phenomenon in an organic crystal α-(BEDT-TTF)2I3 under high pressure. Essentially, it is a semimetal or a narrow gap semiconductor. But, the transport property is peculiar. The conductivity of this the carrier (hole) density and mobility change by a about 6 orders of magnitude. They change in a manner so that the effects just cancel out giving rise to the temperature independent conductivity. At low temperatures, the system is in a state with high mobility (3 × 105 cm2/V·sec) and low carrier density (5 × 1015 cm-3). This state has been found to be very sensitive to magnetic field. We propose a mechanism for the extremely strong temperature dependence of the carrier density. It is based on the band structure and takes the thermal effect into consideration.
  • Yukihiko Takagaki, Klaus H. Ploog
    2000 Volume 69 Issue 2 Pages 552-558
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We investigate the magnetic-field-induced transmission resonance in two-dimensional-electron-gas--superconductor junctions. The magnetic-field correlation of the conductance fluctuations is nonuniversal at low magnetic fields provided the normal region has a certain kind of rectangular-shape. The anomalous magnetoconductance fluctuations are robust against the imperfection of the quantum cavity geometry and the occupation of multiple modes in the normal lead. However, the anomalous fluctuations are suppressed if the cavity size is not sufficiently large in comparison to the lead width. This indicates the importance of multiple Andreev reflection for the anomalous behavior. The wave function at the resonance in the anomalous fluctuations regime reveals scars by regular classical orbits. Hierarchical nature of the anomalous conductance fluctuations is evidenced by the distributions of the current and the charge.
  • Ryusuke Ikeda
    2000 Volume 69 Issue 2 Pages 559-571
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Vortex-glass transitions induced by a line-like disorder, the so-called Bose-glass (BG) transition and two types of Gaussian-splayed-glass (GSG) transitions, are studied on the basis of the lowest Landau level (LLL) approach to the Ginzburg-Landau (GL) model. For each of these transitions, we estimate the transition point and derive critical properties of response quantities just above the transition. A particular attention is paid to the scaling behaviors near GSG transitions of response quantities to a gauge disturbance δ A _⊥ perpendicular to the applied magnetic field B , which are difficult to be derived without explicit calculation. As an example, it is found for the case of planar GSG transition with a well-defined splay plane that the tilt modulus for a tilt parallel to the splay plane has no critical divergence, as in the vortex-glass (VG) transition due to a point disorder, while the corresponding modulus for an out-of-plane tilt is divergent as in BG case and proportional to the correlation length of this transition. The responses to a gauge disturbance δ Az parallel to B are also briefly discussed. It is pointed out that, as a result of a field dependence of glass transition temperature, any glass transition can suppress the first order freezing transition at sufficiently low fields but within LLL approach.
  • Shuji NishiZaki, Yoshiteru Maeno, Zhiqiang Mao
    2000 Volume 69 Issue 2 Pages 572-578
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We report the specific heat of a high-quality single crystal (Tc=1.48 K) of the spin-triplet superconductor Sr2RuO4 under magnetic fields precisely parallel to the basal plane. The field-sweep measurements at low temperatures have revealed the existence of two distinct critical fields. We will argue that the dependence of the energy gap on different Fermi-surface sheets in combination with the in-plane anisotropy of the gap can explain such behavior. Furthermore, the temperature-sweep measurements have clearly revealed an unusual entropy release somewhat below Tc(H) only if the field is greater than 1.2 T. This behavior corresponds well with the second-transition feature recently observed in the ac susceptibility measurements, and provides thermodynamic evidence for the change in the superconducting state.
  • Takao Mori, Takaho Tanaka
    2000 Volume 69 Issue 2 Pages 579-585
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    REB50 (RE=Tb, Dy, Ho, Er) compounds were synthesized and magnetic properties were measured. A measurement of the magnetic susceptibility of TbB50 at high field confirmed the antiferromagnetic transition at 17.5 K. Antiferromagnetic transitions were also observed in the other three compounds with transition temperatures TN ranging from 7.5 K to 4.6 K. These compounds are the first found type of higher boride compounds in which a magnetic transition occurs. The variation of the transition temperatures for the rare earth series indicated that the shortness of the B12 icosahedral bonding length is not the only important factor of the magnetic transition. The resistivity of a REB50 type isostructural compound, a TbB41Si1.2 crystal showed a metallic-type temperature dependence at low temperatures. Electrical and magnetic properties of the REB50 type compounds differ largely from other higher boride compounds such as REB25 and REB66.
  • Tatsuya Kawae, Masaki Mito, Masako Hitaka, Fusao Ichikawa, Toru Shigeo ...
    2000 Volume 69 Issue 2 Pages 586-591
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The electrical resistivity of PrCo2Si2 with a long-period commensurate spin structure has been measured in a magnetic field up to 9 Tesla, together with the heat capacity up to 5 Tesla. The resistivity changes drastically with step-like jumps at the successive transition points accompanying the change of the antiferromagnetic propagation vectors. From the resistivity measurements, four distinct phases are confirmed below the antiferromagnetic transition temperature. A temperature-magnetic field phase diagram of PrCo2Si2 is presented.
  • Peter M. Gehring, Seung–Hun Lee, Kazuma Hirota, Takatsugu Masuda ...
    2000 Volume 69 Issue 2 Pages 592-597
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    Cold neutron inelastic scattering experiments on four CuGe1-xSixO3 single crystals with x=0, 0.004, 0.01, and 0.02 have been performed to study the effects of Si doping on the antiferromagnetic (AFM) and spin-Peierls (SP) excitations with high energy resolution. The intrinsic energy width Γ of the AFM excitation measured along the c * ([001]) direction near the magnetic zone center (0, 1, ½) (q=0) varies as q2 for q le0.032 Å-1 = 0.06qZB. This observation directly supports the recent theoretical predictions of Saito and Fukuyama. For pure CuGeO3 the intrinsic SP excitation energy width appears to be resolution-limited up to 0.085 Å-1. Upon doping, the widths of the SP excitations increase dramatically, but they are weakly q-dependent in the range we investigated. At x=0.02 the SP phase is lost. The existence of a second gap in CuGeO3, first observed by A " in et al., is also confirmed. This second gap, which is quite sharp in the pure compound, is considerably broadened at Si concentrations as low as x=0.004.
  • Makoto Okutani, Takeo Jo
    2000 Volume 69 Issue 2 Pages 598-606
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The spin (Ms) and orbital magnetic moments (Mo) of a Co atom are calculated for various superlattices of Co atoms in fcc Pd or Cu matrix on the basis of the tight-binding model including s, p and d orbits, where the intraatomic multipole interaction between d electrons is taken into account with the Hartree-Fock approximation. A test calculation for pure Fe, Co and Ni with use of parameters obtained by fitting with the first-principles calculation shows that the method well describes the ratio Mo/Ms. Two types of enhancement of Mo of the Co atom in superlattices are proposed based on a semi-quantitative calculation with assuming ferromagnetism. In the Pd matrix, the enhancement is shown to arise from the increase of the lattice parameter, which causes the narrowing of 3d density of states; the atomic environment of a Co atom in the matrix, i.e., the numbers of neighboring Co or Pd atoms are the minor effect. In the Cu matrix, on the other hand, the difference in the effective hybridization in the 3d state between Co-Co and Co-Cu pairs mainly determines the extent of the narrowing of Co 3d states and therefore the extent of the enhancement. If all the nearest neighbors of a Co atom are occupied by Cu atoms, it is shown that Mo can be comparable to Ms.
  • Ming–Fa Lin, Feng–Lin Shyu
    2000 Volume 69 Issue 2 Pages 607-610
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    The low-frequency electronic excitations of a two-dimensional graphite sheet are studied within the self-consistent-field approach. A zero-gap graphite sheet only exhibits the interband e-h excitations at zero temperature. Electrons and holes grow rapidly as temperature increases from zero. Temperature induces the intraband excitations and thus the intraband plasmons. A graphite sheet is predicted to be the first undoped system which could exhibit the low-frequency plasmons purely due to temperature. Whether such plasmons exist are mainly determined by temperature and momentum. The temperature-induced plasmons in a graphite sheet are identified as the 2D plasmons from the momentum dependence of plasmon frequencies. They quite differ from the optical plasmons in the three-dimensional graphite or graphite intercalation compounds. The inelastic light scattering spectroscopies could be used to verify the temperature-induced plasmons.
  • Takenari Goto, Tomohiro Hosokawa, Masumi Takeshima
    2000 Volume 69 Issue 2 Pages 611-617
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    We have found broad band luminescence due to a self-trapped exciton (STE) and disappearance of a free exciton luminescence in ultrathin nanocrystals of PbI2 embedded in ethylene-methacrylic acid copolymer at 77 K. This fact suggests that the STE becomes stable because of a rise in the lowest free exciton level due to size quantization. The Stokes shift in the two- and three- monolayer nanocrystals is found to be larger in comparison with that in more than four monolayer nanocrystals, from luminescence spectra in the size selective excitation. From this larger Stokes shift, it is imagined that a quasi-two-dimensional STE strongly interacts with an acoustic phonon characteristic of the ultrathin crystal. Moreover we observed temporal behavior of the STE luminescence in various excitation intensities. In very weak excitation, the STE luminescence shows a slow single exponential decay with a time constant of 330 μs. This means that an isolated STE in a nanocrystal is in a spin-triplet state and annihilates radiatively. In strong excitation, the STE luminescence decays faster and shows non-exponential decay. From this fact and the additional fact that the quantum efficiency of the STE luminescence is independent of the excitation intensity, it is thought that wave functions of the nearest two STEs overlap with each other, resulting in a singlet-triplet mixing caused by a spin-orbit interaction.
  • Mitsuaki Ginoza
    2000 Volume 69 Issue 2 Pages 618-624
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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    A theory is presented for the solvent-mediated force potential between spherical colloidal particles in a solvent. The long range part of the potential Φ ij(sol)(r) between the i- and j-species of particles is given as Φ ij(sol)(r) =-kBT∑nK(n)di(n)dj(n) 1 over r e-znr with the temperature T and the Boltzmann constant kB, where K(n) and zn are determined by the bulk structure of the solvent and dj(n) is calculated from zn and the structure of the solvent near the j-species of colloidal particle. A similar result is also obtained for the long range part of the total correlation function h0j(r) between colloidal- and solvent-particles. It is discussed that dj(n) is inversely proportional to the isothermal compressibility of the solvent. The application of the theory to the solvent near its critical point gives extremely simple and universal expressions for the asymptotic behaviours of h0j(r) and Φ ij(sol)(r). This Φ ij(sol)(r) is compared with the van der Waals potential in order to emphasize a role of Φ ij(sol)(r).
  • Katsuhiro Itakura, Hiroshi Yasuda, Shu Kurokawa, Akira Sakai
    2000 Volume 69 Issue 2 Pages 625-626
    Published: February 01, 2000
    Released on J-STAGE: July 28, 2000
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