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Ryoya Saji, Hidetoshi Konno
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 2 Pages
361-364
Published: February 01, 1998
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Wavelet transform (WT) of the modulating multiple-soliton solution for the nonlinear Schrödinger (NLS) equation is performed with the use of a hyperbolic function, the one-soliton solution of the NLS equation, as an analyzing wavelet (AW).The uncertainty relation of this new hyperbolic AW is explicitly obtained as Δ x Δ p = π/6. Suitability of the hyperbolic AW is also examined and its performance is compared with that due to the Gabor AW via conventional statistical mechanical quantities such as the mean value, the most probable value, the skewness and the kurtosis of position-momentum (x-p) distribution for modulating solitons.
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Hiroyuki Nagashima, Hitoshi Mahara
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 2 Pages
365-368
Published: February 01, 1998
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We have numerically studied a phenomenon, “the extinction of oscillation”, in a reaction-diffusion system; all the oscillators stop together in a limited region of the system size. In the numerical experiments, we adopted a model of the van der Pol oscillator with or without pacemakers. We found that the extinction of oscillation occurs when the size of the system N is comparatively small. In order to explain the numerical results for the case of no pacemakers, we have developed a theory for the system with the van der Pol oscillators, in which the Dirichlet boundary condition is satisfied. The theory predicts that the system breaks out, extincting the oscillation as expected, when the size of the system N corresponds to a critical size N
c and the oscillators never oscillate for a size N smaller than N
c. The theory also successfully explains the oscillating pattern and its maximum amplitude of the oscillation in the region of a system size larger than N
c.
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Yasuhiro Hieida
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 2 Pages
369-372
Published: February 01, 1998
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We apply the density matrix renormalization group (DMRG) method to a non-equilibrium problem: the asymmetric exclusion process in one dimension. We study the stationary state of the process to calculate the particle density profile (one-point function). We show that, even with a small number of retained bases, the DMRG calculation is in excellent agreement with the exact solution obtained by the matrix-product-ansatz approach.
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Makoto Iima, Sadayoshi Toh
Subject area: Fluid dynamics.
1998 Volume 67 Issue 2 Pages
373-376
Published: February 01, 1998
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To study one elementary process of entropy cascade in hard turbulence, we propose a shell model which governsthe temperature gradient rotated through the angle +\frac{π}{2}, χ ≡ (∂
yT, -∂
xT), and the velocity gradient, i.e., strain rates.This model is based on the correspondence of the dynamics ofχin a two-dimensional free convection system to that of the vorticity in a three-dimensional Navier-Stokes system.We obtain the following results: 1) A steady solution which satisfies Bolgiano-Obukhov (BO) scaling in the viscous case exists.2) After a small disturbance of large scale is added to the steady solution, time series of the modes in the inertial range become similar to each other under the proper scaling, and each mode has its own characteristic time predicted by BO scaling.3) When the same disturbance is added to the null state, the modes also evolve similarly in the inertial range.The characteristic times of the modes are, however, explained by a dimensional analysis based on total entropy which is different from BO scaling.
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Shinya Yoshioka, Yuhji Tsujimi, Toshirou Yagi
Subject area: Equations of state, phase equilibria, and phase transitions.
1998 Volume 67 Issue 2 Pages
377-380
Published: February 01, 1998
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Coherent excitation of the ferroelectric soft modes of KDP has been done in the time domain by femtosecond impulsive stimulated Raman scattering. The observed time dependence shows clearly a relaxational character of the soft mode in a wide temperature range above T
c. A critical slowing-down is directly revealed in the temperature dependence of the relaxation time τ = τ
0 T
0/(T-T
0) as τ
0 is 0.11 × 10
-12 s, where T
0 is the phase transition point of the clamped crystal. The order-disorder phase transition mechanism is reasonable within the limit of the time resolution of the present study.
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Toyoaki Eguchi, Jun Nakamura, Toshiaki Osaka
Subject area: Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties).
1998 Volume 67 Issue 2 Pages
381-384
Published: February 01, 1998
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Scanning tunneling microscopy (STM) has been used to study thesurface structure and electronic states of α-Sn(111) films grownheteroepitaxially on InSb(111)A-(2× 2). The wide area STM imageshows a large number of domains existing on the terrace, each having anaverage size of about 100 Å and a period of (2× 2). The magnified image shows evidence of a T
4-adatom and rest-atom pairreconstructed structure for theα-Sn(111)-(2× 2) surface, as expected from the ab initio calculations. Furthermore, the result that the adatom and therest-atom appear simultaneously in the occupied state image can beexplained by the existence of back bond states in the adatomconfiguration.
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Andrew P. Mackenzie, Shin–ichi Ikeda, Yoshiteru Maeno, Toshizo F ...
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
385-388
Published: February 01, 1998
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Although angle-resolved photoemission spectroscopy (ARPES) has been used for detailed study of the layered perovskite copper-oxide superconductors for nearly ten years, Sr
2RuO
4 is the first metal of this structural class for which it has been possible to obtain detailed Fermi surface data from both quantum oscillations and ARPES. We show that the two techniques give very different results, and present strong evidence that the current interpretation of ARPES data is not representative of the bulk electronic structure of Sr
2RuO
4.
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Kazuhiro Sano, Yoshiaki Ono
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
389-392
Published: February 01, 1998
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Using the numerical diagonalization method, we investigate the one-dimensional d-p model, simulating a Cu-O linear chain with strong Coulomb repulsions. Considering the effect of the transfer energy t
pp between the nearest neighbor oxygen-sites, we calculate the critical exponent of the correlation functions K
ρ based on the Luttinger liquid relations and the ground state energy E
0(φ) as a function of an external flux φ.We find that the transfer t
pp increases the charge susceptibility and the exponent K
ρ in cooperation with the repulsion U
d at the Cu site. We also show that anomalous flux quantization occurs for K
ρ>1.The superconducting region is presented on a phase diagram of U
d vs. t
pp plane.
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Naurang L. Saini, Alessandra Lanzara, Antonio Bianconi, Daniel Law, Al ...
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
393-396
Published: February 01, 1998
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Polarized Cu L-edge X-ray absorption spectra (XAS) measurements of the unoccupied electronic state of 3d_x
2-y
2 symmetry in superconducting La
1.85Sr
0.15CuO
4 single crystals show a temperature dependent anomalous decrease of the density of itinerant holes below -- 100K. The anomalous temperature coincides with the temperature of the metal to insulator (MI) transition and local lattice distortions in the CuO
2 plane. The results give direct evidence of decrease of itinerant states in the CuO
2 plane due to local lattice distortions across the MI crossover in the normal state.
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Yositake Takane, Katsuhiro Nakamura
Subject area: Electronic transport in condensed matter.
1998 Volume 67 Issue 2 Pages
397-400
Published: February 01, 1998
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The ballistic conductance fluctuations (CF) in chaotic billiards are studied using an extended semiclassical approximation. We show that the effect of small-angle diffraction (SAD) on classical electron paths is essential for describing the ballistic CF. By incorporating the SAD effect, we find that both the diffuson and cooperon processes equally contribute to the variance of the transmission coefficient T, in contrast to the result by Jalabert et al. [Phys. Rev. Lett. 65 (1990) 2442] in which only the diffuson process appears. Our result indicates that, in the presence of a magnetic field, the variance of T decreases precisely by a factor of two due to the sensitive suppression of the cooperon contribution. We also determine the full magnetic-field correlation function of T.
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Akinori Tanaka, Toshihiro Idogaki
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
401-404
Published: February 01, 1998
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We present a Hubbard model with a special hopping matrix, which has highly degenerate single-electron energy eigenstatesbut has different properties than the flat-band Hubbard model.Our model has a paramagnetic ground state when the electron filling factor is less than or equal to quarter-filling.In the case of quarter-filling with one extra electron, the present model exhibits saturated ferromagnetism in the ground states for a sufficientlylarge value of on-site Coulomb interaction but does not for a small one.
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Yutaka Moritomo, Yousuke Maruyama, Takumi Akimoto, Arao Nakamura
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
405-408
Published: February 01, 1998
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Anisotropic magnetic and transport properties have been investigated for single crystals of layered-perovskite manganites (La
1-zNd
z)
2-2xSr
1+2xMn
2O
7 as a function of thendoping level x and averaged ionic radius z of the rare-earth ion.The ferromagnetic metallic (FM) state observed in La
1.2Sr
1.8Mn
2O
7 (x=0.4; z=0.0) disappears with increasing x or z, and the ground state is replaced by a layered antiferromagnetic (layered-AF) state beyond x-- 0.5. Thus obtained phase diagram is discussed in terms of variation of the e
g-band structure with the band-filling (=1-x).
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Michinobu Mino, Hisayuki Urakami, Vladimir L. Safonov, Keiichi Zouta, ...
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 Volume 67 Issue 2 Pages
409-412
Published: February 01, 1998
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The parallel pumping of spin waves in an yttrium iron garnet (YIG)sphere placed in a microwave cavity has been performed by X-band microwaves. The onset and the principal frequencyof auto-oscillations above the threshold of spin-wave instabilitywere studied at various magnetic fields. We found anomalous field dependence of auto-oscillations frequency in the low field side of the butterfly curve, where the threshold of parallel pumping instability exhibits no anomaly.This result shows that the higher order nonlinear relaxation process ofparametrically excited magnons becomes important in a nonequilibrium system.
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Jirka Hlinka, Hiroshi Orihara, Yoshihiro Ishibashi
Subject area: Dielectric properties and materials.
1998 Volume 67 Issue 2 Pages
413-415
Published: February 01, 1998
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The temperature dependence of the microwave relaxation in the vicinity of the main polar commensurate phases (q
s/c
*=2/7, 4/15) ofbetaine calcium chloride dihydrate (BCCD) is ascribed to activated overdamped modes on the phason branch. Quantitative results are obtained.
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Laurent C. Duda, Günter Dräger, Satoshi Tanaka, Akio Kotani, ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1998 Volume 67 Issue 2 Pages
416-419
Published: February 01, 1998
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Experimental and theoretical investigations are made for thepolarization dependence in the resonant X-ray emission spectra due to theCu 3d→ 2p electronic transition under the Cu 2p→ 3dresonant excitation (Cu 2p-RXES) in La
2CuO
4. It is shown that thepolarization dependence of the Cu 2p-RXES can be deduced from thespectra obtained under the various geometrical configurations of thecrystal axis, the polarization direction of the incident beam, and the direction of the detector.The calculated results are in fairly good agreement with the experimentalresults.
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Toshinao Akuzawa, Miki Wadati
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 2 Pages
421-425
Published: February 01, 1998
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Studied is the probability density of random hermitian matrices which is naturally obtained by the diffusion on GL(N, C)/U(N). The exact expression for the n-point correlation is obtained by the orthogonal polynomial method. The eigenvalue density is evaluated in the large N limit and the result is compared with the semi-circle law of the Gaussian Unitary Ensemble (GUE). In the analysis, the method developed by Kazakov is made use of.
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Isamu Nakata, Hiroaki Ono
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 2 Pages
426-429
Published: February 01, 1998
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Weakly nonlinear waves in a ferromagnet with dissipation are investigated. By means of reductive perturbation method, the derivative nonlinear Schrödinger equation with a dissipation term is derived and the possibility of propagation of shock waves similar to the limit shock waves in magnetohydrodynamics is shown.
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Alex Yu. Tretyakov, Astero Provata
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 2 Pages
430-433
Published: February 01, 1998
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We study the steady-state behavior of the trimolecular reaction A+2X⇔ 3X on a 2-d square lattice. By viewing the systemas a kind of a percolation problem and finding a rigorous value for thepercolation threshold, we show that a single asymptotic state isrecovered starting from any non-zero concentration of X-particles, unlike on a number of lattices with lower dimensionality and/orcoordination number.
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Elsayed Farouk Elshehawey, Abd El Magied El Misery, Abd El Hakeem Abd ...
Subject area: Mechanics, elasticity, and rheology.
1998 Volume 67 Issue 2 Pages
434-440
Published: February 01, 1998
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The problem of peristaltic transport of a non-Newtonian (Carreau) fluid in a non-uniform channel has been investigated under zero Reynolds number with long wavelength approximation. The problem is formulated using a perturbation expansion in terms of a variant of Weissenberg number. It is assumed that chyme in the male small intestine behave like Carreau fluid since most of the physiological fluid behave like a non-Newtonian fluid. Pressure rise and friction force, in the case of non-uniform geometry, are found much smaller than the corresponding values in the case of uniform geometry. Furthermore, the pressure rise and the friction force are smaller in the case of Carreau fluid than Newtonian fluid. A comparison between Carreau fluid, couple-stress fluid and Casson fluid is given. The pressure rise and friction force are discussed for various of the physical parameters of interest.
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Akihiro Ishizawa, Yuji Hattori
Subject area: Fluid dynamics.
1998 Volume 67 Issue 2 Pages
441-450
Published: February 01, 1998
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The wavelet analysis is performed on the numerical results of two-dimensional magnetohydrodynamic (MHD) turbulence. By virtue of simultaneous resolutionin scale and position of wavelet decomposition, the intermittent nature is well captured. The whole region is successfully divided into the two regions with different inertial subranges of energy spectra: the turbulent region with E
T(k) ∝ k
-3/2 and the coherent region with E
T(k) ∝ k
-2. The local energy transfers by convection of velocity field and by stretching of magnetic field are probably responsible for the transition of turbulent state into coherent state.
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Katsunori Yoshimatsu, Mitsuaki Funakoshi
Subject area: Fluid dynamics.
1998 Volume 67 Issue 2 Pages
451-461
Published: February 01, 1998
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The pattern selection in Faraday surface water waves caused by the instability of the state of no waves is examined under the assumption of high aspect ratio. First, nonlinear evolution equations for the amplitudes of resonant capillary-gravity waves with different directions of wavenumber vector are derived. These equations include cubic nonlinearity and the effects of viscous damping and parametric forcing obtained from the energy equation. Then, using the method of a center manifold, quintic amplitude equations for unstable modes are derived in which cubic damping and forcing are included. From these equations, it is concluded that the squares are stable for sufficiently short waves, the hexagons and the 8-fold quasipatterns are stable when the wavelength is within two intermediate regions, and the stripes are always unstable.
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Takashi Sakajo, Hisashi Okamoto
Subject area: Fluid dynamics.
1998 Volume 67 Issue 2 Pages
462-470
Published: February 01, 1998
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The fast summation method of Draghicescu is applied tocomputation of 2D vortex sheet motion.This paper reports our numerical experiments which show the effectiveness as well as difficulties of Draghicescu's fast summation method in 2D vortex-sheet computations. For instance, the fast summation method is nearly thirty times faster than the direct summation method when we use 65536 = 2
16 vortex blobs. As a test problem, we re-examine Krasny's problem of computing a vortex sheet for a fairly long time.
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Sumio Kogoshi, Sigehiro Mishimagi, Keiichi Yoshii, Joji Maeda
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 2 Pages
471-476
Published: February 01, 1998
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A circle mapping can approximately reproduce the cross section of magnetic surfaces and the value of the periodic driving force (K) at a magnetic island varies with the width of the magnetic island, which suggests the value of K is one of measures for the degradation of magnetic surfaces. The profile of a rotational transform has flat regions at the magnetic islands. The width of the flat region is proportional to the width of the magnetic island. Therefore it may be another measure of the degradation of magnetic surfaces. This method requires less data for the estimation than the usual method of calculating the width of magnetic islands. For collapsed magnetic surfaces that are produced by overlapping of two magnetic islands, the fractal dimension can effectively estimate the degradation of them. The fractal dimensions of cross sections of regular magnetic surfaces and clear magnetic islands are nearly 1, while that of a collapsed magnetic surface is about 1.2 in the present study.
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Itsuo Ishikawa
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 2 Pages
477-480
Published: February 01, 1998
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Electron collision processes in a plasma with negative ions that were generated by feeding a small amount of SF
6 gas into a contact ionization plasma (e.g., Q-machine plasma) were numerically analyzed using a collision-in-cell model. The numerical results are as follows.The density of SF
6- is predominant, and is over four times that of SF
5-'s. Many of the electrons which underwent vibrational collision, attach to SF
6 in subsequent collisions. The electron density can be controlled in a wide range depending on SF
6 gas pressures.
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Hiroyuki Kitaoka, Toshikazu Yamamoto, Katsumi Hirano
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 2 Pages
481-486
Published: February 01, 1998
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Characterization of soft X-ray emission from a plasma focus device with Ar gas puff is carried out. Intensities of the K-shell lines are observed quantitatively and spectroscopically in a single shot. Depending on the delay time between the puffing of the Ar and the main discharge, the generated soft X-ray source in the pinched plasma is divided into two categories, namely filamentary or scattered spot sources. The soft X-ray intensity of the filamentary source is much higher than that of the scattered spot sources. It is observed that the absorption by the surrounding plasma is remarkable. Using an imaging Bragg spectrometer, spatial distributions of soft X-ray images depicted by the H-like Lyα line, the He-like resonance line, the He-like intercombination line and the Li-like dielectronic satellite lines of Ar ions are obtained. It is recognized that the image from Lyα, the other lines and unresolved pinhole image form a nest with a common center. Although the He-like resonance line is especially subject to remarkable absorption, we restored the observed intensity and evaluate the spatial distribution of the electron temperature and the electron density.
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Kohtaro Orito, Tadatsugu Hatori
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 2 Pages
487-494
Published: February 01, 1998
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The behaviors of the nonlinear dipole vortex in the drift unstable plasma are studied by numerical approaches.Model equations used in numerical simulation are derived from two-fluid model and are composed of two equations with respect to the electrostatic potential and the density perturbation.When the initial dipole vortex is inclined at some angle with respect to the direction of the drift velocity, the dipole vortex oscillates or rotates in the first stage.These phenomenon also happen in the stable system.In the second stage, one part of the dipole vortex grows and another decays because of the destabilization.The shrunk vortex rotates around the enlarged vortex.Consequently, a monopole vortex appears out of the dipole vortex.
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Jirka Hlinka, Yoshihiro Ishibashi
Subject area: Equations of state, phase equilibria, and phase transitions.
1998 Volume 67 Issue 2 Pages
495-498
Published: February 01, 1998
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Recent experimental investigations of the dielectric anomaly inside the fourfold modulate phase of betaine calcium chloride dihydrate by Le Maire et al. (T
s-anomaly) is analysed in the framework of Landau theory. Suggested symmetry for the structure is P2
1ca (above T
s) and P1c1, P11a or P2
111(below T
s), respectively.It is shown that biquadratic coupling between primary order parameter with the B
2 mode (inducing the P2
1ca to P11a phase transition ) may provide consistent explanation of Le Maire et al.'s results.
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Makoto Iwata, Akira Miyashita, Yoshihiro Ishibashi, Keiichi Moriya, Sh ...
Subject area: Equations of state, phase equilibria, and phase transitions.
1998 Volume 67 Issue 2 Pages
499-501
Published: February 01, 1998
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The dielectric dispersion in single crystals of stannous thiohypodiphosphate, Sn
2P
2S
6, which shows ferroelectricity at room temperature, was measured in the frequency range between 100Hz and 10MHz below room temperature. We found that the non-Debye type dielectric dispersion appears below 100, K. From the dielectric dispersion, we determined the activation energy and the attempt frequency by assuming the Arrhenius relation. The nature of the orientational dynamics in the dipole system of Sn
2P
2S
6 was discussed.
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Akihiro Murakami, Takashi Sakuma, Haruyuki Takahashi, Yoshito Onoda
Subject area: Thermal properties of condensed matter.
1998 Volume 67 Issue 2 Pages
502-504
Published: February 01, 1998
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The phase transition of cation substituted CuBrTe, Cu
xAg
1-xBrTe system, was investigated by a specific heat measurement in the temperature range between 100K and 523K. Cu atoms are substituted by Ag atoms in the range of 0.85≤ x≤ 1. The new phase β
′ was observed in the range of 0.85≤ x≤ 0.9825. The obtained phase diagram of Cu
xAg
1-xBrTe system was confirmed by X-ray diffraction measurements. The characteristics of the X-ray diffraction patterns at the phase transitions of Cu
xAg
1-xBrTe system were mentioned.
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Tadao Ishii, Toshinori Abe
Subject area: Transport properties of condensed matter (nonelectronic).
1998 Volume 67 Issue 2 Pages
505-512
Published: February 01, 1998
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The relaxation mode (relaxon) theory is applied to a superionic conductor superlattice, which leads to minibands of relaxon eigenvalues E
q and a non-Debye dynamic conductivity σ (ω) therefrom. It is made clear that non-diffusive relaxons of zero wave number q = 0, made of extended and localized modes, give rise to the frequency exponent s in Reσ (ω)≈ σ
0 + Aω
s in two ways: especially for the extended modes, the square of a mode diffusion length is approximately of hyperbolic type 1/E_{q = 0}
a with non-integer exponent α, which results in s≈ 0.6. The localized mode, on the other hand, works for the other type of non-Debye behavior of s≈ 1.
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Fanyao Qu, Paulo César de Morais
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
513-518
Published: February 01, 1998
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The ground state binding energy of hydrogenic impurities in n-doped and undoped GaAs--Al
xGa
1-xAs quantum wells, under intense high-frequency polarized laser field is investigated. The calculation has been performed by means of a nonperturbative theory and variational approach which takes into account the “dressed” confinement barrier potential, the “dressed” Coulomb potential, and the screening effect due to the two-dimensional electron gas. We found that the impurity binding energy in a n-doped quantum well is dramatically reduced by both, the screening effect and the intense high-frequency laser field, thus leading, under certain circumstances, to a metal-insulator transition.
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Tin Cheung Au–Yeung, Zhi Fei Shi, Chan Hin Kam, Rajesh Menon, Ro ...
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
519-524
Published: February 01, 1998
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We use a variational perturbative method for the calculation of the energy levels of impurity magnetopolarons in parabolic quantum wires. The method is reasonable for all electron-phonon coupling α, all Rydberg constant R, all parabolic frequency ω and all cyclotron frequency ω
c. The ground state and first excited state energies are computed by the method and their dependence on α, R, ω and ω
c is discussed.
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Fusayoshi J. Ohkawa
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
525-534
Published: February 01, 1998
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Four types of magnetic exchange interactions, which work between quasiparticles, are investigated within the theoretical frameworkof the virtual exchange of bosons or bosonic excitations.Three types of exchange interactions are due to the virtual exchange of high-energy spin excitations, pair excitations of electrons far from the chemical potential through the spin channels.They are characterized by a pair of intermediate states in the exchange process; the conventional superexchange interaction is characterized by a pair of occupied bands, an extended superexchange interaction by a pair of unoccupied bands, and an extended Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction by a pair of an occupied band and an unoccupied band.These three types of exchange interactions are present in both insulating and metallic states.The fourth one is a novel exchange interaction due tothe virtual exchange of low-energy spin excitations, pair excitations of quasiparticles through the spin channels, and scales with an effective bandwidth of quasiparticles. This exchange interaction is present only in metallic states.The extended RKKY and the novel exchange interactionscan be ferromagnetic for specific band structures. All of these four exchange interactions can be Cooper-pair interactions.
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Fusayoshi J. Ohkawa, Koji Onoue, Hiroyuki Satoh
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 2 Pages
535-542
Published: February 01, 1998
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The crossover between itinerant-electron magnetism and local-moment magnetism is investigated using the Hubbard moderson model.Intersite spin fluctuations are considered by the 1/d-expansion method, with d being the spatial dimensionality. When there is substantial nesting of the Fermi surface, the staggered susceptibility shows a Curie-Weiss-like temperature dependence.This Curie-Weiss law is of leading order in 1/d or O [ (1/d)
0 ].When the Néel temperature T
N is so low that T
N << T
K, with T
K being the local Kondo temperature, ordered magnetic moments are tiny.The ratio of the specific heat jump to the totalspecific heat at T
N is approximately proportional to the ratio of the nested area of the Fermi surfaceto the total Fermi surface.When there is strong quenching of magnetic moments by local quantum spin fluctuationsand nesting of the Fermi surface is substantial enough, a sinusoidal magnetic structure stabilizes.Otherwise, a helical magnetic structure stabilizes.
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Ikuo Ichinose, Tetsuo Matsui, Kazuhiko Sakakibara
Subject area: Superconductivity.
1998 Volume 67 Issue 2 Pages
543-550
Published: February 01, 1998
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We present a quantitative study of the charge-spin separation (CSS) phenomenon in a U(1) gauge theory of the t-J model of high-T
c superconductors.We calculate the critical temperature T
CSS of a confinement-deconfinement phase transition as a function of hole doping δ, below which the CSS takes place. Fluctuationsof gauge fields are so large that T
CSS is reduced to about 10% of its mean-field value. We also make some comments on the phase structure from a gauge-theoretical point of view.
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Yoji Ohashi, Satoshi Takada
Subject area: Superconductivity.
1998 Volume 67 Issue 2 Pages
551-559
Published: February 01, 1998
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The plasma mode in the superconducting state is studied within the random phase approximation. It is proved that the plasma oscillation in the limit of zero momentum (q) is not affected by the superconductivity. This statement itself has been obtained so far under some special conditions where energies of the plasma frequency and the superconducting order parameter are much different. In this paper, we clarify that it holds true at all temperatures irrespective of (1) the magnitude of the plasma frequency, (2) the symmetry of the order parameter, and (3) details of the system, e.g., dimensionality and the layered structure. We also show that the plasma sum-rule is satisfied even in the superconducting state, which states that the spectrum of the density-density correlation function in the limit q→ 0 is dominated by the plasma mode only. Although the phase fluctuation of the order parameter couples with the charge one, the collective phase oscillation, so-called the Carlson-Goldman mode, does not contribute to the spectrum of the density-density correlation function in this limit.
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Shuji Nishizaki, Yoshiteru Maeno, Snorre Farner, Shin–ichi Ikeda ...
Subject area: Superconductivity.
1998 Volume 67 Issue 2 Pages
560-563
Published: February 01, 1998
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We measured the specific heat of single crystals of non-cuprate layered perovskite superconductor Sr
2RuO
4. The crystals with different T
c up to 1.2, K exhibit a large residual electronic coefficient γ
0, which decreases systematically with increasing T
c. This behavior is consistent with the presence of nodes in the superconducting gap and with the variations of T
c due to pair breaking by impurities and defects. To quantitatively account for the observed large γ
0, however, we need to introduce additional mechanism.
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Nobuyuki Katoh, Masatoshi Imada
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
564-575
Published: February 01, 1998
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Effects of possible orbital order in magnetic properties of two-dimensional spin gap system for CaV
4O
9 are investigated theoretically. After analyzing experimental data, we show that single orbital models assumed in the literature are insufficient to reproduce the data. To understand the origin of the discrepancy, we assume that in d
1 state of V, d
xz and d
yz orbitals have substantial contributions in the lowest-energy atomic level which leads to a double-degeneracy. We study possible configurations of the orbital order. By exact diagonalization and perturbation expansion, we calculate the susceptibility, wavenumber dependence of low-lying excitations and equal-time spin-spin correlations which is related to integrated intensity of the neutron inelastic scattering. These quantities sensitively depend on the configuration of the orbital order. The calculated results for some configurations of the orbital order reproduce many experimental results much better than the previous single-orbital models. However some discrepancy still remains to completely reproduce all of the reported experimental results. To understand the origin of these discrepancies, we point out the possible importance of the partially occupied d
xy orbital in addition to orbital order of partially filled d
xz and d
yz orbitals.
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Jinbo Yang, Bo Cui, Weihua Mao, Yingchang Yang, Dongfeng Chen, Jilian ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
576-582
Published: February 01, 1998
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Structure and magnetic properties of YFe
10Mo
2 and YFe
10Mo
2N compounds have been studied with neutron diffraction and self-consistent spin-polarized linear muffin-tin orbital (LMTO) band calculation. The diffraction results indicate that the nitrogen atoms are located at 2b sites with nearly 99\
esults for site-dependent Fe magnetic moments and hyperfine fields. The interstitial-atom effect on the local magnetic moments and hyperfine fields is explained with magneto-volume effect and chemical bonding effect. The contributions of the magneto-volume effect and the chemical bonding effect of the nitrogen to the magnetic moments (μ
Loc), Fermi-contact hyperfine fields (H
FC) and isomer shifts (IS) are reported.
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Yoshio Kuramoto, Noboru Fukushima
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
583-593
Published: February 01, 1998
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A dynamical effective medium theory is presented for quantum spins andhigher multipoles such as quadrupole moments.The theory is a generalization of the spherical model approximationfor the Ising model, and is accurate up to O(1/z_n) where z_n isthe number of interacting neighbors.The polarization function is optimized under the condition that it bediagonal in site indices. With use of auxiliary fields and path integrals, the theory isflexibly applied to quantum spins and higher multipoles with manyinteracting neighbors.A Kondo-type screening of each spin is proposed for systems withextreme quantum fluctuations but without conduction electrons.
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Shigeru Takayanagi, Hitoshi Sugawara, Pavel Svoboda, Rikio Settai, Yos ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
594-598
Published: February 01, 1998
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We have investigated the specific heat of NdCu
2 at temperatures between 0.6 and 10 K in magnetic fields up to 6 T, applied along the three crystal axes of the orthorhombic structure. We have determined a magnetic phase diagram, in which more than seven phases have been identified for the field applied along the {b}-axis.
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Takehiko Hihara, Kenji Sumiyama, Ying Wang, Tomoaki Kamiyama, Kimio Wa ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
599-603
Published: February 01, 1998
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Granular Fe
xCu
100-x films have been produced by a cluster beam (CB) technique. Small angle X-ray scattering (SAXS) measurements indicate that the geometrical size of Fe clusters is about 5, nm in diameter for x=13. Magnetization and magnetoresistance curves between 5 and 300, K can be fitted to the Langevin functions with taking account of the Fe cluster size distribution and an inter-cluster magnetic interaction. The average magnetic cluster size estimated from these analyses is about 1.6, nm (180 atoms) for T≥ 50, K, which is roughly consistent with SAXS observation. However, smaller size distribution of about 0.6, nm (10 atoms) is obtained from the same analysis of the results at T=5, K. This implies a magnetic size-down originated from a magnetic frustration at low temperature.
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Akinori Tanaka, Toshihiro Idogaki
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
604-611
Published: February 01, 1998
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Through the method of reflection positivity, we prove the existence of long range order associated with dipoleand quadrupole moments at finite temperature on the classical bilinear-biquadratic exchange Hamiltonian.We also obtain an upper bound on the dipole phase transition temperature, and find that there is a range of bilinear and biquadratic exchange interaction parameters for which the quadrupole phase transition temperature lies above the dipole one.
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Takeshi Matsumura, Shintaro Nakamura, Terutaka Goto, Hiroshi Amitsuka, ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
612-621
Published: February 01, 1998
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The magnetic susceptibility, elastic constant, specific heat and magnetization of the magnetic semiconductor TmTe have been measured in detail. A phase transition which is likely to be an antiferro quadrupolar ordering was found to occur at 1.8 K. The specific heat measurements under magnetic fields along the three main crystal axes revealed the unusual characters of this phase transition. The (H-T) phase diagram below 5 T is very similar to that of the antiferro quadrupolar ordering in CeB
6. Above 5 T, however, the phase line for H || [100] begins to close toward T=0 K. The physical properties in the paramagnetic region at high temperatures are discussed in the mean field approximation. The theoretical fitting of the elastic softening indicates the antiferro inter-ionic quadrupolar interactions. However, the mean field theory can not explain the specific heat results.
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Akihisa Koga, Seiya Kumada, Norio Kawakami, Takahiro Fukui
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
622-628
Published: February 01, 1998
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We investigate low-energy properties of a generalized spin ladder model with both of the spin alternation and the bond alternation, which allows us to systematically study not only ladder systems but also alternating spin chains.By exploiting non-linear σ model techniques we study the model with particularemphasis on the competition between gapful and gapless states.Our approach turns out to provide a more consistentsemi-classical description of alternating spin chains than that in the previous work. We also study a closely related model, i.e., a spin chain with plaquette structure, and showthat frustration causes little effect on its low-energy properties so far as the strength of frustration is weaker than a certain critical value.
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Masafumi Sera, Masahiko Hiroi, Norio Kobayashi, Satoru Kunii
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
629-635
Published: February 01, 1998
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We have studied the transport properties of NdB
6 single crystal under the magnetic fields up to 15, T between 2, K and 15, K. The Hall resistivity is constant in the paramagnetic region but shows an increase with decreasing temperature below T
N, which indicates the decrease of a carrier concentration in the antiferromagnetic (AF) state. This originates from the cut of the Fermi surface by super-zone in the AF state. Both resistivity ρ and specific heat exhibit roughly T
2 dependence below -- 6, K, being different from those expected for a usual AF metal. This suggests a finite contribution of magnons in ferromagnetic layers in the type I AF structure to low energy excitations of NdB
6. There exists no indication of the resistivity anomaly due to the AF ordering around T
N. In the paramagnetic region, ρ decreases and a thermal conductivity κ increases but a Lorentz number L decreases with increasing magnetic field. The former two properties originate from a suppression of large Q spin fluctuations by the magnetic field but the latter indicates that the inelastic spin-flip scattering becomes important with magnetic field. The magnetic field dependences of ρ, κ and L is very small in the AF state, which indicates that the probability of the spin-flip scattering is not changed by the magnetic field.
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Rikio Settai, Singo Araki, Parhat Ahmet, Melike Abliz, Kiyohiro Sugiya ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
636-644
Published: February 01, 1998
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We have studied the origin of the cooperative Jahn-Teller effect and themetamagnetic transition in the orthorhombic compound PrCu_2.We have determined the anisotropic ferroquadrupole phase diagram bymeasuring the specific heat and thermal expansion under magnetic fields.With increasing the field, the Jahn-Teller transition temperature increasesslightly for the field along a- and c-axes, while it decreases intensively along the b-axis.The phase diagram can be explained quantitatively by including thequadrupolar interaction of-K
JT‹ O
xy › O
xyin the crystalline electric field and Zeeman Hamiltonian.The metamagnetic transition, which brings about the conversion between theeasy (a)- and hard (c)-axes magnetization, has beenalso studied through the magnetostriction.This phenomenon is also explained quantitatively on the basis of thequadrupolar interaction of-K
M‹ O
22 › O
22.The sign of ‹ O
22 › is found tobe negative in the state where the c-axis is thehard one, while it changes from negative to positive above themetamagnetic transition field.
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Kazuma Hirota, Masashi Hase, Jun Akimitsu, Takatsugu Masuda, Kunimitsu ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
645-650
Published: February 01, 1998
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The magnetic excitations of CuGe
1-xSi
xO
3 single crystals(x=0.011 and 0.03) have been studied by inelastic neutron-scattering techniques. We confirm the coexistence of the antiferromagnetic and spin-Peierls excitations as well asa splitting of the antiferromagnetic excitation peak at the magnetic zone center (q=0)due to orthorhombic anisotropy. The q dependence of the antiferromagnetic spin-wave widthΓ scales well with q
2 for small q (q<0.1 Å
-1). We also find thatthe spin-wave velocity increases as the size of induced magnetic moment becomes larger. These experimental results strongly support recent theoretical predictions by Saito andFukuyama.
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Makoto Izumi, Kazuyuki Nakazawa, Yoshichika Bando
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 2 Pages
651-654
Published: February 01, 1998
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The transverse and longitudinal magnetoresistivities of SrRuO
3/SrTiO
3 superlattices on SrTiO
3 (001) substrates were measured to study low-dimensional effects on the magnetic properties of SrRuO
3. Both the differential resistivity, dρ (T)/dT, and magnetoresistivity, {Δ}ρ (H)=ρ (H)-ρ (0), become maximum at the ferromagnetic transition temperature, T
C. The transition appears when the SrRuO
3 layer is as thick as 2 unit-cells or more. The T
C decreases quickly with decreasing thickness, especially for less than 4 unit-cell thickness.
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Hiroshi Orihara, Masaru Sugaya, Kozo Tajiri, Yoshihiro Ishibashi, Masa ...
Subject area: Dielectric properties and materials.
1998 Volume 67 Issue 2 Pages
655-657
Published: February 01, 1998
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Dielectric measurement was carried out on an immiscible blend of a side-chain type polysiloxane liquid crystalline polymer (LCP) and a poly-dimethylsiloxane (PDMS), which has a large electrorheological (ER) effect, in the frequency range from 100, Hz to 10, MHz and over the temperature range from 25°C to 105°C. Two relaxation processes were observed; one is due to the mesogenic motion, i.e., the δ -process of LCP and the other to the Maxwell-Wagner effect originating in the conductivity of LCP dispersed in PDMS. The results were analyzed in terms of the Clausius-Mossotti (CM) approximation and the local field exerted on droplets of LCP was discussed.
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