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Farhan Saif
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2363-2366
Published: 2000
Released on J-STAGE: November 30, 2000
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We investigate quantum revivals in the dynamics of an atom on a modulated atomic mirror moving under the influence of gravitational field. This system constitutes Fermi accelerator for atoms. It is demonstrated that the external driving field influences the revival time significantly. Analytical expressions are presented which are based on semiclassical secular theory. These analytical results explain the dependence of the revival time on the characteristic parameters of the problem quantitatively in a simple way. They are in excellent agreement with numerical results.
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Satoshi Yukawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2367-2370
Published: 2000
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A quantum analogue of the Jarzynski equality is constructed. This equality connects an ensemble average of exponentiated work with the Helmholtz free-energy difference in a nonequilibrium switching process subject to a thermal heat bath. To confirm its validity in a practical situation, we also investigate an open quantum system that is a spin 1/2 system with a scanning magnetic field interacting with a thermal heat bath. As a result, we find that the quantum analogue functions well.
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Jiro Mizushima, Yusuke Hara
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2371-2374
Published: 2000
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Transitions of natural convection in a tilted rectangular cavity heated from below are investigated numerically and theoretically by assuming two-dimensional and incompressible flow fields. All the boundary walls are assumed to be perfectly thermally conducting. It is known that thermal convection in a horizontal cavity heated from below occurs above a critical Rayleigh number due to an instability and has almost the same integral number of cells as the aspect ratio of the cavity, whereas natural convection in a vertical cavity heated from one side wall occurs even for very small Rayleigh (or Grashof) numbers and exhibits unicellular global circulation. Routes from multicellular convection to unicellular convection when the cavity is inclined gradually from the horizontal plane are explored by bifurcation analyses of the numerical results.
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Haruhisa Koguchi, Yoshiki Maejima, Yoichi Hirano, Yasuyuki Yagi, Toshi ...
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2375-2378
Published: 2000
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In high theta discharges of the reversed field pinch (RFP) plasma on TPE-1RM20, it is observed that the soft X-ray signal ramps up when the amplitude of the magnetic fluctuations concentrates into a single helical mode (poloidal mode number, m=1, and toroidal mode number, n=7). Even in an extreme case where the fluctuation level of this single mode becomes quite large, as large as that in ordinary cases with a factor of about five, the soft X-ray signal is still sustained at a high level. This result indicates that the single helical state can play an important role in the improvement of plasma confinement in RFP. This assumption is confirmed by the results of the nonlinear magnetohydrodynamics (MHD) simulations of RFP plasma. The simulation shows that the single helical state can have a significant closed magnetic surface area. On the other hand, the large stochastic area of the magnetic field lines always appears in the case of the multihelical modes of the magnetic fluctuations. The numerical results of time variations of the m=1 mode amplitudes with different n values are quite similar to those of experimental observation in a low theta discharge.
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Koh Saitoh, Michiyoshi Tanaka, An Pang Tsai, Chris J. Rossouw
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2379-2382
Published: 2000
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Two-dimensional channelling patterns, derived from variations in characteristic X-ray emission rates as a function of incident electron beam orientation, have been recorded from an Al
72Ni
20Co
8 decagonal quasicrystal for the first time. These channelling patterns indicate that the Al and transition metal atoms occupy different sets of sublattice sites, and that (to a good approximation) both Ni and Co atoms randomly occupy a similar set of sublattice sites, i.e. they are mutually disordered. This is shown to support the view that the structure of this alloy is determined primarily by the number of electrons per atom, e/a.
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Wei Sun, Tetsu Ohsuna, Kenji Hiraga
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2383-2386
Published: 2000
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We have found a highly perfect quasiperiodic superstructure of a decagonal quasicrystal (D-phase), which is formed by the ordered arrangement of atom columnar clusters. The D-phase with 0.4 nm periodicity, which has been found in a conventionally solidified Al
70Ni
20Ru
10 alloy, shows many superlattice reflections in its tenfold electron diffraction pattern. High-resolution electron microscopy of the D-phase reveals that the ordered arrangement of two types of atom columnar clusters with different directions of pentagonal symmetry allows the fundamental lattice of a pentagonal tiling to be subdivided into two sublattices of rhombic tilings with edge length enlarged τ times (τ is the golden ratio).
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Yoshihiro Yamazaki, Tsuyoshi Mizuguchi
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2387-2390
Published: 2000
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The aggregation process of granules driven by the motion of water-air fronts in the drying process of two-dimensional wet granular systems is experimentally studied. The fronts and aggregated granules interact with each other during this drying, and a labyrinthine pattern is formed as a result. A qualitative framework of the pattern formation is given, and topological and metrical properties of the pattern are also discussed.
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Jan van Elp, Hitoshi Sato, Tsuyoshi Kimura, T. Toda, Y. Okamura, Yoshi ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2391-2394
Published: 2000
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Using polarized oxygen K edge spectroscopy, the first unoccupied orbital of LaSrMnO
4 was investigated. The lowest unoccupied orbital is of minority spin d
xz, d
yz character instead of the majority spin d
x2-y2 character. The d
x2-y2 orbital would be expected based on Hund's rule and the strong exchange interaction of the one-electron addition d
5 system. The explanation is a strong ligand field splitting caused by the strong local site distortion of the Mn site which raises the energy of the majority spin d
x2-y2 orbital and lowers the energy of the d
xz, d
yz orbitals. At the same time the two-electron integrals, which are responsible for the exchange interaction, are screened because of covalency.
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Shuichi Murakami, Naoto Nagaosa
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2395-2398
Published: 2000
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We study theoretically the multicritical phenomena of the superconductivity (SC) and antiferromagnetism (AF) in organic conductors κ-BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) salts. The phase diagram and the experimental data on the nuclear magnetic resonance (NMR) relaxation rate 1/T
1 is analysed in terms of the renormalization group method. The bicritical phenomenon observed experimentally indicates the rotational symmetry, i.e., SO(5) symmetry, of the SC and the AF. The critical exponent x for the divergence of 1/T
1 is well explained by x = ν ( z - 1 - η) with the dynamical exponent z = 3/2 for the AF region while z = φ/ν ∼ 1.84 at the bicritical point. These results strongly suggest that the origin of the SC is in common with that of the AF and that its symmetry is d-wave.
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Hong Bin Huang, Tatsuya Shishidou, Takeo Jo
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2399-2402
Published: 2000
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The difference in Mn L
2,3 X-ray absorption spectrum between polarizations parallel and perpendicular to the c-axis, i.e., linear dichroism (LD), is discussed for LaMnO
3, where 3d orbits 3x
2-r
2 and 3y
2-r
2 are suggested to align ``antiferromagnetically'' in the a-b plane. By a calculation on the basis of a single-ion model including the intraatomic 3d-3d and 3d-2p multipole interactions and a crystal field, we show that the basic multiplet structure of the LD spectrum strongly reflects 3d orbital ordering and is insensitive to the Jahn-Teller distortion of the MnO
6 octahedra. LD is, therefore, shown to be a promising method to observe directly orbital ordering.
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Eiji Saitoh, Yasuhide Tomioka, Tsuyoshi Kimura, Yoshinori Tokura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2403-2406
Published: 2000
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Raman scattering spectra have been investigated for a single crystal of Sm
1-xSr
xMnO
3 (x=0.45) showing prototypical colossal magnetoresistance (CMR). The emergence of broad phonon bands above the Curie temperature T
c is ascribed to dynamical charge/orbital ordering coupled with local lattice distortion, while concomitant anisotropic diffuse scattering to directional ordering of orbital. The temperature-dependent Raman spectral features can be closely correlated with the resistive and magnetic anomalies as well as the X-ray diffuse scattering peak around T
c of this compound, verifying an important role of the orbital correlation in the CMR.
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Gen Tatara, Hidetoshi Fukuyama
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2407-2410
Published: 2000
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The dephasing effect of the electron by boundary magnetic field is investigated theoretically in a multilayer structure of a nonmagnetic conduction layer sandwiched by ferromagnetic layers. The induced moment at the interface is shown to cause dephasing if a spin mixing mechanism such as spin-orbit interaction is present. This effect suppresses the anti-localization due to the spin-orbit interaction and is stronger when the magnetization of the two layers are parallel to each other, contributing to an anomalous positive magnetoresistance close to a switching field at low temperatures.
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Takao Morinari, Manfred Sigrist
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2411-2414
Published: 2000
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The London penetration depth for the unconventional superconductor Sr
2RuO
4 is analyzed assuming an order parameter which breaks time-reversal symmetry and parity simultaneously. Such a superconductor possesses gapless chiral quasiparticle states at the surface. We show that these subgap states contribute significantly to the low-temperature behavior of the London penetration depth, yielding a T
2 power law even though bulk quasiparticle spectrum is gapped. The presence of several electron bands gives rise to interband transition among the subgap surface states and influences the properties of the surface impedance. The surface states also lead to a nonlinear Meissner effect.
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Takashi Nishioka, Hitoshi Mukai, Setsuji Nakamura, Gaku Motoyama, Yasu ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2415-2418
Published: 2000
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We have made high pressure magnetization measurements on a single crystalline URu
2Si
2 up to P = 1.61 GPa, in magnetic fields up to 15 T and in the temperature range between 4.2 and 100 K. A characteristic temperature T
0 which corresponds to an antiferromagnetic phase transition shows a slight increase with pressure, while T
max, at which the temperature dependence of the magnetization exhibits a maximum, remains nearly constant with pressure. We have also observed that the pressure dependence of the high field magnetization at low temperatures shows a shallow minimum at around 1 GPa, in contrast to a strong and monotonic increase in a staggered magnetic moment revealed by recent elastic neutron diffraction experiments under pressures. To reconcile this discrepancy, we suggest, in conjunction with other experimental results, that the observed large staggered moment in the neutron diffraction experiments is not static but fluctuating in time.
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Nobuhisa Okazaki, Kiyomi Okamoto, Tôru Sakai
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2419-2422
Published: 2000
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We study the magnetization process of the S=1/2 antiferromagnetic spin ladder in the presence of the second and the third-neighbor couplings which lead to frustration with the typical nearest-neighbor coupling. We use degenerate perturbation theory and level spectroscopy analysis of the numerical diagonalization data of the Hamiltonian for finite systems. We find two kinds of plateaux at half the saturation moment in the magnetization curve. One is mainly due to the second-neighbor couplings and the other to the third-neighbor couplings. The mechanisms of these two plateaux are quite different with each other.
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Taichi Terashima, Chieko Terakura, Yuji Umeda, Noriaki Kimura, Haruyos ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2423-2426
Published: 2000
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Magnetization and resistivity were measured as functions of temperature and magnetic field on two single crystals of CaB
6 and three of (Ca
0.995La
0.005)B
6. One of the doped crystals exhibited ferromagnetism with the magnetic moment of 0.32μ
B/La at 10 kOe and 5 K, while the other two were paramagnetic, displaying the Curie law below 120 K with the effective magnetic moment of 1.3 or 2.0μ
B/La. We propose that the sample-dependent magnetic behaviors of (Ca
0.995La
0.005)B
6 may be explained in terms of superparamagnetism, assuming that the ferromagnetic state is spatially inhomogeneous. All the samples exhibited the metallic behavior of electrical conduction. Quantum oscillations were found in the magnetoresistance of one of the doped crystals. The angular dependence of the oscillations, however, indicates that their origin is not the sample bulk.
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Kazuki Ohishi, Tetsuya Yokoo, Kazuyuki Kakuta, Hirokazu Fujino, Takash ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2427-2430
Published: 2000
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A strongly modulated Néel order has been inferred from muon spin relaxation (μSR) measurement in Sr
2.5Ca
11.5Cu
24O
41 below T
N = 2.2 ± 0.1 K in conjunction with the previous result of neutron scattering. This is consistent with the scenario of staggered moments induced by the partial destruction of the singlet ground state by localized holes. Comparison of the μSR result with that in an isostructural compound La
3Sr
3Ca
8Cu
24O
41 indicates that the static magnetic order is induced by appropriate hole carriers at both chain and ladder layers.
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Nobuyasu Haga, Sei–ichiro Suga
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2431-2434
Published: 2000
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The NMR relaxation rates of (quasi-)one-dimensional spin-gapped systems such as the S=1/2 spin ladder with a diagonal interaction and the Haldane-gap system are investigated at low temperatures in magnetic fields. We show that in the regime where the gap is collapsed by magnetic fields, the NMR relaxation rate diverges with decreasing temperature and its exponent shows a behavior characteristic of the model as a function of the magnetic field. We discuss our results and compare them with recent experimental findings for the spin ladder system Cu
2(C
5H
12N
2)
2Cl
4 and for the Haldane-gap system (CH
3)
4NNi(NO
2)
3.
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Yoshiaki Kobayashi, Takeshi Miyashita, Makoto Ambai, Toshihiko Fukamac ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2435-2438
Published: 2000
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Nuclear quadrupole resonance of the in-plane Cu of YBa
2Cu
3O
y (y=6.61) has been carried out to investigate if the ``wipeout'' phenomenon, which is observed in La
2-x-yNd
ySr
xCuO
4 and La
2-xSr
xCuO
4 and is considered to be related to the slowdown of the charge fluctuation and possibly to the ``stripe'' formation, can also be found for the system in the 60 K plateau region of the oxygen number y. No evidence for such a phenomenon has been found, indicating that the origin of the plateau cannot easily be connected to the existence of the fluctuating ``stripe'' in the system.
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Chari Ramkumar, Takao Aoki, Ryo Shimano, Yu. P. Svirko, Tomofumi Kise, ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2439-2442
Published: 2000
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We employ a pump-induced polarization rotation scheme for the quantitative study of four-particle (exciton-exciton) correlations in a strongly coupled semiconductor microcavity. From the measured rotation angle in the χ
(3)-regime, in which the nonlinear response is linearly proportional to pump intensity (I
pump), we evaluate the absolute value of anharmonicity of two-dimensional excitons. Deviation from the χ
(3)-regime is observed beyond I
pump=0.2kW/cm
2.
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Naoaki Bekki, Takao Karakisawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2443-2454
Published: 2000
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The phase-lockings of quasi-periodic solutions for a dissipative fifth-order system of magnetoconvection are numerically observed when a certain parameter is varies. It is shown that a phase-locking series of torus creates a devil's staircase as the magnetic Prandtl number is varied. It is also numerically demonstrated that there exists a kind of invariant phase-locked torus and its rational winding number is 5/7. Such a phase-locking series of torus is significantly different from the Fibonacci's sequence related to the KAM-torus. A relation between hierarchies of winding numbers is leading to some scaling-laws.
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Tatsuo Shibata, Ken Sekimoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2455-2462
Published: 2000
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We present the energetic aspect of open systems which may exchange particles with their environments. The motion of the particles is described by the classical Langevin dynamics. We study the energy balance relation among the open system and the environments along a particular realization of the stochastic process. It is clarified how much energy each particle carries when it enters or leaves the system. This energy is definitely different from the chemical potential. Then, the chemical potential is consistently interpreted from the viewpoint of energetics, paying attention to the difference of the level of description between the thermodynamics and the kinematics.
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Hirofumi Morise, Miki Wadati
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2463-2467
Published: 2000
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The phase separation and collective excitations of two-component Bose-Einstein condensates in traps are studied. Using the variational method, we show that the separated state is favorable in the case where the interspecies interaction is strongly repulsive and the number of atoms is large enough. This phase separation condition is explained in terms of the softening of a dipole mode collective excitation. Other low-lying excitation modes and their softenings which lead to the instability of the mixed state are also studied by use of the sum-rule approach.
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Katsunori Yoshimatsu, Mitsuaki Funakoshi
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2468-2478
Published: 2000
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Third-harmonic resonance of capillary-gravity waves in two-dimensional Faraday waves due to the parametric excitation of the lower-frequency mode is examined for infinite depth. The amplitude equation incorporating both a small detuning from this internal resonance and that from the external resonance with the vertical oscillation of a container is derived using the method of reductive perturbation and also including a linear damping. This equation has mixed-wave solutions: periodic and chaotic solutions as well as stationary solutions. Moreover, we find two more hysteresis regions of stationary solutions, in addition to the hysteresis region observed for a single-mode Faraday wave. Some periodic solutions become chaotic through a series of period-doubling bifurcations.
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G. P. Raja Sekhar, Osamu Sano
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2479-2484
Published: 2000
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The effect of the presence of a circular void or a spherical void of characteristic size R
0 in a porous media with permeability k on an otherwise undisturbed uniform flow U
∞ is investigated analytically. The entire flow field is determined by matching the solution of the Stokes equation inside the hole with that of the generalized Darcy's (Brinkman) equations in the porous region. The effect of the hole increases with the value of ζ
0 = R
0/√k. When ζ
0 is much greater than unity, which corresponds to the case for typical groundwater flow, the velocity at the centre of the circular cylindrical hole U
0 becomes 3 U
∞, while the volume flux Q
0 flowing into the hole from upstream-side becomes twice, in comparison with Q
∞ that flows into the same region in the absence of the hole. On the other hand, the velocity at the centre of the spherical void U
0 becomes 6 U
∞, while Q
0 becomes 3Q
∞.
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Toru Kuroda, Hideo Sugama, Ryutaro Kanno, Masao Okamoto
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2485-2492
Published: 2000
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Linear properties of ion temperature gradient (ITG) modes in toroidal helical systems are studied. The real frequencies, growth rates, and eigenfunctions are obtained for both stable and unstable cases by solving a kinetic integral equation with proper analytic continuation performed in the complex frequency plane. Based on a model magnetic configuration for toroidal helical systems like the Large Helical Device (LHD), dependences of the ITG mode properties on various plasma equilibrium parameters are investigated. Particularly, relative effects of ∇ B-curvature drifts driven by the toroidicity and by the helical ripples are examined in order to compare a ITG modes in helical systems with those in tokamaks.
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Md. Khairul Islam, Yousuke Nakashima, Kiyoshi Yatsu, Isao Katanuma, Da ...
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2493-2497
Published: 2000
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The first results of Langmuir probe measurements at the outer transition region of the anchor cell of GAMMA10 are given. A probe current asymmetry in vertical direction is found in this region. It is also found that the asymmetry of probe current increases in outward direction and the direction of the asymmetry is independent on movable limiter position. A relation of this plasma asymmetry with the main magnetic field configuration is investigated. Plasma flow through the non-axisymmetric magnetic field configuration region is thought to be the source of plasma asymmetry in this region, i.e., ∇ B and curvature drifts are responsible for the asymmetry. Possibility of cold plasma formation in the anchor cell region is obtained during plug electron cyclotron resonance heating (ECRH) and can be explained with the desorption of particles due to the collision of the drifted out particles with the wall.
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Chunguang Du, Shiqun Li
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2498-2502
Published: 2000
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The dynamics of a charged particle interacting with a short laser pulse propagating in a plasma is studied analytically and numerically. It is shown that the dynamics of a positive particle is quite different from that of a negative one of the same absolute charge-mass ratio, except for the case of ultrashort pulses (L<<λ
p). A positive particle may be accelerated to very high energy even when both the pulse intensity and the particle injection energy are low. The dependence of the particle dynamics on the pulse length is studied in detail.
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Jun–ichi Sakai, Takuya Nakayama, Yoshihiro Kazimura, Sergei Bula ...
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2503-2513
Published: 2000
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Relativistic plasma streaming in background plasmas becomes unstable against the Weibel-type electromagnetic instability, which is one of effective mechanisms of magnetic field generation in cosmic plasmas. It is shown by using 3-D fully relativistic particle-in-cell (PIC) simulation code that magnetic fields perpendicular to the stream in an electron-positron (pair) plasma are generated in the early stage of the instability with small-scale sizes of the electron skin-depth. In the subsequent nonlinear stage there occurs magnetic reconnection which causes to make large-scale structure of magnetic fields in pair plasmas. The magnetic field dissipation through the magnetic reconnection leads to heating of the background plasma. These sequential physical processes are important for understanding of magnetic field generation in the relativistic shock of gamma-ray burst (GRB) sources in astrophysical plasmas.
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Saiko Negishi, Hiroshi Negishi, Minoru Sasaki, Masasi Inoue
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2514-2530
Published: 2000
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Monte Carlo simulations of atomic distribution of intercalated guest atoms in the layered 1T-TiS
2 have been performed by taking into account attractive or repulsive pair-interactions between the neighboring guest atoms in the a-axis plane and along the c-axis of the crystal lattice (lattice size for computation: 18× 18× 6). X-ray diffraction patterns are calculated from the atomic distributions obtained using four kinds of pair-interactions, in qualitative agreement with the experimental data of the 2a× 2a× 2c short-range ordered structure for x=0.15, and superlattices of 2√3a× 2a× 2c for x=0.25 and √3a×√3a× 2c for x=0.333 with fractional site occupancy in Fe
xTiS
2. From the calculated atomic distributions, we have evaluated the number of neighboring guest atoms, the formation of clusters, and percolation cluster, as well as its dimension, all of which are responsible for the dynamical relaxation behaviors of the thermoremanent magnetization observed in the spin- and cluster-glass phases of Fe
xTiS
2. Using the present results and EXAFS data, we have further discussed on the change in the local structures near the host sulfur atoms by intercalation of the guest atoms in M
xTiS
2.
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Takanori Ito, Kazume Nishidate, Mamoru Baba, Tsutomu Sato, Koichi Shin ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2531-2535
Published: 2000
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For (n,n) single-walled carbon nanotubes of the so-called armchair type , size and temperature dependence of dynamical structure factors at the zone center and zone boundary have been studied by molecular dynamics simulations using an order-N tight-binding method. Dynamical structure factors have been calculated through the Fourier transform of the time correlation function of the particle density obtained from molecular dynamics simulation results. This scheme allows a non-perturbative calculation of temperature-dependent anharmonic effects. It has been shown that the dynamical structure factors of the transverse optical mode at the zone center strongly depend on diameter of carbon nanotubes of the armchair type in good agreement with the results by the lattice dynamics calculation based on C-C force constants. It has been furthermore expected that a frequency shift of the longitudinal optical mode at the zone boundary with increasing temperature is much larger than that of the transverse optical mode at the zone center.
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Ji–wen Liu, Yu–qiang Ma
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2536-2542
Published: 2000
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We introduce vacancy-mediated diffusion mechanism to consider the effect on the phase separation kinetics of water-in-oil microemulsions. It is found that the vacancy plays different roles at low and high quench temperatures, due to the competition between the vacancy-mediated segregation dynamics and the reduction of driving force for the phase separation. For deep quench case, vacancies prefer to locate at interfaces and speed up the phase separation by increasing the atomic diffusions at interfaces. As the quenched temperature is increased, vacancy-mediated diffusion process is gradually balanced by the reduction of interfacial tension because a large amount of vacancies immigrates inside the bulk of phase. On the contrary, all the amphiphile molecules are still adsorbed onto interfaces and is not sensitive to the temperature change because the entropy change is small compared with the strong interface energy change induced by the chain properties of the amphiphiles.
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- Relaxation Mode Theory -
Tadao Ishii, Toshinori Abe
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2549-2558
Published: 2000
Released on J-STAGE: November 30, 2000
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On the basis of the relaxation mode theory in a noninteracting lattice gas, the anomalous dynamic conductivity Re σ(ω)=σ(0)+Aω
s+A
'ω
s', $s\approx 0.6$, $s^{\prime}\approx 1$ is fully examined in a random supercell system having a uniform distribution of the activation energies U
min≤U≤U
max; the low-frequency and high-temperature region Aω
s is governed by the extended nondiffusive modes, while the high-frequency and low-temperature region A
'ω
s' is regulated by the localized nondiffusive modes. The dynamical crossover exists in-between. The frequency power s is almost independent of temperature but s
' changes with it. The coefficient approximately given by $A\approx\beta\exp\{-\beta(1-s)U_{{\
m max}}\}$ shows a strong temperature dependence since $s\approx 0.6$, and $A^{\prime}\approx\beta\exp\{-\beta(1-s^{\prime})U_{{\
m min}}\}$ depends but weakly on temperature because $s^{\prime}\approx 1$. All these characteristics, which are quite consistent with the experiments of Nowick
et al., are originated in a single mechanism of the mode diffusion length $L_{\varepsilon}\approx\ au_{\varepsilon}^{\alpha/2}$ and density of states $D_{\varepsilon}\approx\ au_{\varepsilon}^{\delta}$ where τ
ε is the mode relaxation time.
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Jun–ichi Koizumi, Yo–ichi Kawashima, Rio Kita, Toshiaki Do ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2543-2548
Published: 2000
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Phase equilibrium near the critical double point (CDP) was studied in pressure p-temperature T-volume fraction φ space for the system polystyrene (PS) in cyclohexane (CH). The it
p-T critical lines measured for the molecular weight M
w× 10
-5=1.15, 7.19 and 15.6 had a minimum, i.e., CDP at elevated pressures and were used to determine the free energy of the system on the basis of the Flory-Huggins equation. An analysis of the free energy predicted that CDP appeared at atmosphere for M
w=7.93× 10
4 and disappeared for larger molecular weights. For M
w× 10
-4=7.5 and 3.7 the coexistence curve in
p-φ space were measured by increasing pressure from atmosphere near to 6 MPa and the critical exponent β
p for the volume fraction difference φ
+-φ
-∼ (p-p
c)
βp were determined to be β
p=0.62± 0.03 and 0.39± 0.02, respectively. The former value is close to the doubly enhanced critical exponent at CDP and the latter value is considerably larger than the theoretical value β=0.327 at the usual critical point. On light of the molecular weight dependence of β
p calculated from the free energy, the observed values of β
p was found to reveal the crossover from the usual critical point to CDP.
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Yasunori Kaneta, Shuichi Iwata, Tadao Kasuya, Osamu Sakai
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2559-2576
Published: 2000
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The Fermi surface structures of CeSb in the ferromagnetic (F) phase and in the ferrimagnetic AFF1 phase are studied. The p-f mixing model explains various anomalous magnetic properties of this compound and predicts the β
4 hole surface in the F phase. But the β
4 surface in the previous calculation has the discrepancy from the observations of the de Haas-van Alphen effects. The fully polarized |j=5/2,j
z=5/2> state has been assumed as the occupied orbit of the 4f state. We show that the discrepancy is largely reduced when the occupied 4f state has a little more amplitude of a Γ
7 component than the fully polarized state, although unresolved deviation still remains. The calculated Fermi surfaces of the AFF1 phase explain well the experimental results. The β
4 surface in the F phase changes to the folded and open structure in the AFF1 phase showing new extremal areas. It is shown that the β
4 surface has a very anisotropic mass enhancement factor, which is consistent with the p-f mixing model. As the mechanism to improve the agreement, various types of many body effects are discussed.
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Chisa Hotta, Hidetoshi Fukuyama
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2577-2596
Published: 2000
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Theoretical study on the effect of high Fe spin S=5/2 on the organic two-dimensional electronic system of BETS compounds is made by the calculation with the mean-field approximation for the Coulomb interaction. It turned out that a relatively smaller value of on-site Coulomb interaction, U=U
BETS, on BETS sites compared with that of ET makes the nature of ground states sensitive to the band structure which are characterized by two different types of molecular arrangement, λ- and κ-type. The λ-type system with a smaller band overlap shows a Mott-like insulating state, while the large band overlap of the κ-type favors a nobel spin density wave (SDW)-like state newly found in our study. In both states, the spin amplitude is increased by the exchange interaction, J, between Fe spins and BETS electrons. Our results are summarized in the unified phase diagram, where at a fixed value value of U
BETS close to the metal-insulator boundary, even a small value of J as well as the difference in the band structure changes the nature of state drastically, which fact is in accordance with the experimental reports, and the various ground states of the whole BETS family are explained within the same scheme.
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Satoshi Fujimoto
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2597-2603
Published: 2000
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We study the strong correlation effects in the vicinity of the Mott metal-insulator transition using coupled clean or disordered Hubbard chains with a infinitely large coordinate number D
⊥→∞ in the direction perpendicular to the chains and with a long-range transverse hopping. Strong electron correlation effects are treated partially non-perturbatively with the use of the exact results for the 1D Hubbard model. In the case of clean systems, the thermodynamic and transport quantities which characterize the Mott transition from the Fermi liquid state, such as the specific heat coefficient, the Drude weight, and the compressibility, are obtained as functions of hole-doping δ=1-n (n, electron density) by the systematic expansion in terms of the inverse of the transverse hopping range l
⊥. We find that the δ-dependence of these quantities shows non-universal behaviors with exponents depending on the strength of electron-electron interaction. In the presence of disorder, it is shown that the frequency-dependence of the dynamical conductivity obeys the Mott's law, implying the possibility of
Mott glass state for δ → 0, provided that there exists a finite range interaction.
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Ryo Kurita
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2604-2608
Published: 2000
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Mechanisms of the current modulation due to the gate bias in charge-density-wave field-effect-transistors (CDW FETs) with a NbSe
3 channel were investigated. It was clarified that the CDW dislocations do not modulate the CDW current and that the current is modulated under the gate electrode. The current modulation in the high-temperature CDW phase of NbSe
3 also was observed, for the first time.
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Dai Aoki, Narumi Watanabe, Yoshihiko Inada, Rikio Settai, Kiyohiro Sug ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2609-2614
Published: 2000
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We succeeded in growing a high-quality single crystal of UAl
3 with the cubic AuCu
3-type structure and studied the Fermi surface properties by measuring the de Haas–van Alphen (dHvA) effect and the magnetoresistance, together with the electrical resistivity, magnetic susceptibility and specific heat. Seven dHvA branches were observed, ranging from 1.1× 10
6 to 1.5× 10
8 Oe. These branches are partially explained by the result of band calculations based on the 5
f-itinerant band model. The detected cyclotron mass is in the range from 3 to 17m
0, suggesting the strong 5
f hybridization with the conduction electrons, which is twice to three times larger than the corresponding band mass.
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Shugo Suzuki, Susumu Okada, Kenji Nakao
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2615-2622
Published: 2000
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We investigate the superconductivity in alkali-metal-doped C
60, A
3C
60. (A=K, Rb, etc.) To take account of both the electron-electron and electron-phonon interactions, we employ a model introduced in our previous study for explaining the reason why A
2C
60 and A
4C
60 are, in contrast to A
3C
60, insulators despite that these materials are expected to be good metals. It is found that the superconductivity can also be explained on the same basis that is essential for explaining the anomaly in A
2C
60 and A
4C
60. The origin of the superconductivity in our model is the dynamic Jahn-Teller effect; the attractive interaction between the t
1u electrons is caused by the dynamic Jahn-Teller effect resulting from the pair transfer interaction originated in the coupling between the t
1u electrons and the H
g intramolecular phonons. The order parameter of the superconductivity is spin-singlet and of the A
g symmetry. We also point out that the dynamic Jahn-Teller mechanism revealed here is closely related to the Suhl-Kondo mechanism. The multiplicity of the t
1u bands is indispensable for both mechanisms.
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Kenji Ohoyama, Takahiro Onimaru, Hideya Onodera, Hiroki Yamauchi, Yasu ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2623-2628
Published: 2000
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We report magnetic properties and the phase diagram of NdB
2C
2 which has the same tetragonal LaB
2C
2 crystal structure as that of the antiferroquadrupolar ordering material, DyB
2C
2. NdB
2C
2 is an uniaxial anisotropic antiferromagnet with T
N = 8.8K. The propagation vector in the magnetic ordered state below T
N is
k=[1 0 0]; the coupling between the nearest neighbour magnetic moments in the c-plane is antiferromagnetic, and that along the [0 0 1] direction is ferromagnetic.
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Peter Terzieff, Yoshimi Tsuchiya
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2629-2633
Published: 2000
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The anomalous composition dependence of the magnetic susceptibility in liquid Ag–Ga and Ag–In is investigated within the nearly free electron approximation using simple pseudo-potential theory. The characteristic humps on the silver rich side and the subsequent minima at higher contents (30 at.%) of polyvalent metal are well reproduced by the theory. These features are found to be primarily due to a pronounced modulation of the diamagnetic part of the electronic susceptibility induced by the interactions between the ionic cores and the conduction electrons. The theoretical temperature coefficients of the magnetic susceptibility are in good agreement with the experiment. Unlike to the magnetic susceptibility they pass through a minimum on the silver rich side followed by a maximum at 30 at.% of polyvalent metal, which suggests that the anomalies of the susceptibility vs. composition curve tend to disappear with increasing temperature. Similar to gold based liquid alloys the minima in the electronic susceptibility coincide with the appearance of solid electron compounds at the formal valence electron concentration of about 1.6 electrons per atom.
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Hiroaki Onishi, Seiji Miyashita
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2634-2641
Published: 2000
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We investigate thermodynamic properties of a one-dimensional S=1/2 antiferromagnetic Heisenberg model coupled to a lattice distortion by a quantum Monte Carlo method. In particular we study how spin and lattice dimerize as a function of the temperature, which gives a fundamental process of the spin-Peierls transition in higher dimensions. The degree of freedom of the lattice is taken into account adiabatically and the thermal distribution of the lattice distortion is obtained by the thermal bath algorithm. We find that the dimerization develops as the temperature decreases and it converges to the value of the dimerization of the ground state at T=0. Furthermore we find that the coupling constants of spins fluctuate quite largely at high temperature and there thermodynamic properties deviate from those of the uniform chain. Doping of non-magnetic impurities causes cut of the chain into short chains with open boundary. We investigate thermodynamic properties of open chains taking relaxation of the lattice into consideration. We find that strong bonds locate at the edges and a defect of the bond alternation appears in the chain with an odd number of sites, which causes enhancement of a staggered magnetic order. We find a spreaded staggered structure which indicates that the defect moves diffusively in the chain even at very low temperature.
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Munetaka Sasaki, Koji Nemoto
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2642-2646
Published: 2000
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We study the effect of temperature shift on aging phenomena in the Random Energy Model (REM). From calculation on the correlation function and simulation on the Zero-Field-Cooled magnetization, we find that the REM satisfies a scaling relation even if temperature is shifted. Furthermore, this scaling property naturally leads to results obtained in experiment and the droplet theory.
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Tetsuo Honma, Yoshihiko Inada, Rikio Settai, Shingo Araki, Yoshihumi T ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2647-2659
Published: 2000
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We have studied the magnetic and Fermi surface properties in a ferromagnet UGa
2. The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5f
2- and 5f
3-CEF schemes, based on the localized 5f-electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5f
2- and 5f
3-core models nor by the spin-polarized 5f-itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2m
0, which is consistent with the electronic specific heat coefficient of 11 mJ/K
2·mol.
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Jun Kikuchi, Kazuhiro Ishiguchi, Kiyoichiro Motoya, Masayuki Itoh, Kaz ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2660-2668
Published: 2000
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Magnetic properties of a quasi one-dimensional magnet CuV
2O
6 have been studied by means of susceptibility measurement, NMR and powder neutron diffraction. Cu
2+ spins (S=1/2) order antiferromagnetically below 22.6 K, and the saturation moment is about 0.70μ
B at 0 K. The magnetic structure determined in the present study indicates that in CuV
2O
6 one-dimensional antiferromagnetic spin chains are along [110], suggesting a dominant antiferromagnetic exchange interaction between the next-nearest-neighbor spins rather than the nearest-neighbor ones.
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Hidenori Kubo, Kazuko Zenmyo, Masahiko Tokita, Manabu Matsumura, Kazuy ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2669-2674
Published: 2000
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Proton NMR measurements at low temperature show that Mn moment direction in Mn formate di-urea easily changes by temperature as well as the replacement of hydrogen with deuterium atom in urea. The change in the moment direction is due to the competition of the magnetic anisotropy caused by the dipole interaction with the anisotropy caused by the surrounding ligand ions. The observed spin structure of four-fold screw rotations of antiferromagnetic layers is well understood by very small interlayer exchange interactions and magnetic anisotropies. The possibility is pointed out that the dipole interaction between the first nearest neighboring layers is the important origin of the transition to the three-dimensional long range order of this compound.
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Yoichi Uehara, Yoshihide Suzuki, Sukekatsu Ushioda
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2675-2683
Published: 2000
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We have developed a theory of electron energy loss spectra (EELS) for reflection geometry that includes the electromagnetic retardation effect. This theory analytically reduces to the standard EELS result when $\frac{\omega}{c}$ is much smaller than |
k//|, where ω and
k// are the frequency and the wavevector parallel to the sample surface, respectively, of an elementary excitation created in the scattering process. As a concrete example we calculate the energy loss probability for a Au sample including the electromagnetic retardation effect.
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Norio Ogita, Yoshinori Fujita, Yoshifumi Sakaguchi, Yuichi Fujino, Tak ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2684-2690
Published: 2000
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Polarized Raman scattering spectra of Sr
14-xCa
xCu
24O
41 have been measured for x=0 and 11.5 at ambient pressure. In the spectra, the intra-molecular vibrations due to the unit structure of (Sr/Ca)
2Cu
2O
3 and CuO
2 have been clearly observed below 700cm
-1. A comparison of the number of the observed peaks with the results of a factor group analysis indicates that the crystallographic symmetry of the ladder is F
222 for x=0 and 11.5, instead of centro-symmetric F
mmm, while that of the chain is A
mma for both compositions. However the symmetry of the chain for x=11.5 is close to F
222 or F
mmm. That is, the structure of the chains changes from an incomplete staggered structure to almost complete staggered one with increasing x. In the (c,c) and (a,a) spectra, the broad two-magnon peaks have been observed at around 3000cm
-1. From the analysis of the recent theory of the magnetic scattering in the 2-leg spin ladder system done by Natsume
et al., the following magnetic parameters for x=0 are obtained: J
leg=151 meV, J
rung=91 meV, and Δ
ladder=44 meV. The values agree with those reported by neutron scattering.
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Vu Van Hung, Hoang Van Tich, Kinichi Masuda–Jindo
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 8 Pages
2691-2699
Published: 2000
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The self-diffusion in metals is studied using the moment method in the statistical dynamics including the anharmonicity effects of lattice vibrations. The Gibbs free energy of a metal lattice containing thermal vacancies is derived using the fourth order moment approximation. The interaction energies between the atoms in metals are estimated by using the effective pair potentials. The activation energy Q and pre-exponential factor D
0 of the self-diffusion coefficient are given in closed forms. The activation energy Q and pre-exponential D
0 values are calculated for Fe, Ag, Ta, and W metals at high temperature region near the melting temperature as well as at low (liquid Helium) temperatures, and they are shown to be in good agreement with the experimental results.
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