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Shuichi Nakamura, Tetsuji Konishi, Akihiko Kitada
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
335-336
Published: February 01, 1996
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In our previous paper (S. Nakamura, T. Konishi and A. Kitada: J. Phys. Soc. Jpn. 64 (1995) 731), we topologized a polycrystal by labeling the axes of each single crystal within the polycrystal. In this paper, we propose another topologization of polycrystal which is independent of the labeling of the axes, and the order of the vectors in the base. This natural topologization still conserves the completeness of the polycrystal and, therefore, the existence within it of a compact set with self-similarity is still guaranteed.
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Saburo Kakei
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
337-339
Published: February 01, 1996
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In this letter, we show that the Fredholm determinantD(λ;t), introduced by Zamolodchikov in his study of 2Dpolymers, is the continuum limit of the soliton solution for the Todalattice hierarchy with a 2-periodic reduction condition.
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Hiroshi Kakuhata, Kimiaki Konno
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
340-341
Published: February 01, 1996
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A generalized inverse scheme of the integrable, dispersionless system is proposed from the group theoretical point of view.
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Isao Sawada
Subject area: Statistical physics and thermodynamics.
1996 Volume 65 Issue 2 Pages
342-344
Published: February 01, 1996
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Three decades ago, the quantum Langevin-like equation (Mori formula) was used to reformulate the linear response theory (Kubo formula) in the continued fraction formalism.Since then, the Mori formula has often been used to evaluate transport coefficients, but only within the Born approximation. Very recently, a rigorous closed-form solution to the Mori formula for transport coefficients has been obtained. In the present study, we prove the equivalence of the closed-form solution to the Mori formula and the Kubo formula using the general relations between correlation functions and then comment on the Born approximation.
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Shinji Chiba, Yasuji Sawada
Subject area: Electricity and magnetism: fields and charged particles.
1996 Volume 65 Issue 2 Pages
345-347
Published: February 01, 1996
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In this letter we report the observation of nonlinear dynamics of a needle rotator system placed in a strong homogeneous electric field, in which each rotator couples with others through long-range Coulomb interaction. Nonlinear dynamics of the single rotator and that of two rotators which have different parameters from each other are studied. Bifurcation including locked and unlocked states and hysteresis phenomena are demonstrated. The rotator system proposed here will provide the first globally coupled mechanical oscillator system.
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S. Ridwan, H. Mujamilah, M. Gunawan, P. Marsongkohadi, Q. W. Yan, P. L ...
Subject area: Structure of liquids and solids; crystallography.
1996 Volume 65 Issue 2 Pages
348-350
Published: February 01, 1996
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High-resolution neutron powder diffraction study of Dy
2Fe
9Al
8 has been carried out at 65K. The crystallographic parameters and magnetic moments were determined by Rietveld profile fitting calculation. The results showed that Dy
2Fe
9Al
8 crystallized in the rhombohedral Th
2Zn
17 type structure. The aluminum atoms were distributed randomly at positions 18f, 18h and 6c. The magnetic moments of all iron atoms were parallel to the six-fold axis and couple antiferromagnetically to the moment of Dy.
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Tadao Ishii
Subject area: Transport properties of condensed matter (nonelectronic).
1996 Volume 65 Issue 2 Pages
351-353
Published: February 01, 1996
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On the basis of the relaxation mode (relaxon) theory, a relaxation function which expresses the time dependence of hopping conduction in a many-ion system on a regular lattice and with a screened Coulomb interaction, is analytically and numerically discussed. It is shown that the hyperbolic and stretched-exponential relaxations determine the non-Debye behavior in the low-temperature, short-time region and in the high-temperature, long-time region, respectively.
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Yasuhiro Yamauchi, Mark V. Kartsovnik, Takehiko Ishiguro, Masahiro Kub ...
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 2 Pages
354-357
Published: February 01, 1996
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The angle-dependent magnetoresistance oscillation (AMRO) and Shubnikov-de Haas oscillation are investigated in the layered organic superconductor κ-(BEDT-TTF)
2Cu[N(CN)
2]Cl under pressure.It is found that the AMRO amplitude increases with pressure.The AMRO local maxima observed under -- 8 kbar are periodic in scale of tan θ.Analysis based on the generalized two-dimensional Fermi surface model reveals that the orthorhombic symmetry is broken.
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Shin Nakamura, Junichi Ohtake, Noriyoshi Yonezawa, Shuichi Iida
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 2 Pages
358-360
Published: February 01, 1996
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Hexagonal potassium cobalt oxide KCo
2O
4, with lattice parameters of a=2.846Å and c=12.417Å, has been prepared using KCO
3 and Co
3O
4 as starting materials. The specimens show metallic conduction, with almost linear decrease in the resistivity, in the order of 10
-2, Ω · cm, down to 12K. The magnetic susceptibility is of the order of 10
-6, emu/g and shows paramagnetic behavior.
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Kazuhiro Kuboki, Manfred Sigrist
Subject area: Superconductivity.
1996 Volume 65 Issue 2 Pages
361-364
Published: February 01, 1996
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It is shown that a locally time-reversal symmetry breaking state can occurat Josephson junctions between unconventional superconductorsdue to the angular structure of their pair wave function. The origin is the order parameter induced by the proximity effect at the junction, which can combine with the bulk order parameter with a nontrivial relative phase.Experimental consequences of this effect in high-temperature superconductors are examined.
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Tetsuro Asahata, Akira Oguri, Sadamichi Maekawa
Subject area: Superconductivity.
1996 Volume 65 Issue 2 Pages
365-368
Published: February 01, 1996
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We study the superconducting (SC) states with d_{x
2-y
2} and extended s symmetry in the three-band Hubbard model on a CuO
2 planeusing the variational Monte Carlo method in the limit U
d → ∞, where U_d is the Coulomb repulsion between holes on a Cu site.By comparing the energy among the SC, paramagnetic (PM), and antiferromagnetic (AFM) states, we obtain a phase diagram and find thatthe d_{x
2-y
2}-wave SC state becomes the lowest energy statenear the phase boundary between the PM and AFM phases.In contrast to the d_{x
2-y
2}-wave SC state, the energy of the extended s-wave SC state is always higher than that of the AFM state.
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Tetsuya Mutou, Dai S. Hirashima
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
369-371
Published: February 01, 1996
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Magnetic susceptibility of a periodic Anderson model defined in infinitedimensions is investigated using the quantum Monte Carlo method.Special attention is paid to the enhancement of the interband contributionto the susceptibility (the Van Vleck term). It is found that the interbandcontribution is enhanced by the electron-electron interaction, but theenhancement is weaker than the dynamical mass enhancement.In particular, when the mixing between conduction electrons and f-electronsis small compared to the bandwidth, the enhancement of the interbandcontribution becomes much smaller than the dynamical mass enhancementas the interaction becomes strong.
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Masashi Hase, Yoshitaka Sasago, Kunimitsu Uchinokura, Kazuma Hirota, G ...
1996 Volume 65 Issue 2 Pages
372-375
Published: February 01, 1996
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Cu
3WO
6 has a unique structure in which Cu
2+ (S=1/2) ions are arranged in six-spin rings. Susceptibility measurements imply a spin-singlet ground state with a spin gap.In order to elucidate magnetic excitations, we performed inelastic neutron scattering on a Cu
3WO
6 powder sample. Two peaks are observed at 11 and 14 meV in energy spectra at low temperatures, indicating singlet-triplet excitations. The gaps are temperature independent.There is almost no dispersion in the magnetic excitations. The intensity around 11 meV decreases rapidly with increasing temperature. Constant-ω scans for the 11 meV peak exhibit an oscillating Q-dependence, which we ascribe to a structure factor of the ring. These results are in qualitative agreement with a simple model of an isolated S=1/2 six-spin ring with first, second and third nearest-neighbor antiferromagnetic exchange interactions.
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Aya Ishigaki, Toru Moriya
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
376-378
Published: February 01, 1996
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The low-temperature specific heat around the ferromagnetic instability is studied by using the self-consistent renormalization (SCR) theory of spin fluctuations with particular attention to the crossover between the Fermi liquid (γ T+η T
3ln T+· · · ) and the quantum critical (-Tln T) regimes.
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Osamu Morikawa, Hideyuki Arai, Masaaki Ashida, Satoshi Hashimoto, Riso ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
379-382
Published: February 01, 1996
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A sample of alkali halide crystal with a thin layer of high-concentration O
2- centers has been prepared by infiltration of KO
2 or Na
2O
2 melt into a crack which is artificially introduced in a host crystal. A thin layer of O
2- centers is formed by simultaneous diffusion of O
2- molecules into the host crystal through the crack interfaces. Concentration of the O
2- centers in the layer amounts to -- 2× 10
19, cm
-3, about 10 times higher than that in ordinary samples grown by the Kyropoulos method. As-prepared thin layers have been found to show luminescence spectra characteristic of the O
2- center, though zero-phonon lines of the spectra show large inhomogeneous broadening and their phonon sidebands are deformed markedly. Upon annealing, the width of inhomogeneous broadening is reduced and the spectra approach those of ordinary samples. It has been found that annealed samples show superfluorescence.
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Ignace Loris, Ralph Willox
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
383-388
Published: February 01, 1996
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We investigate how one may write the soliton solutions of a nonlocal Boussinesq equation in Wronskian form, and subsequently prove the existence of N-soliton solutions making use of the bilinear form of this equation. This technique also allows us to construct a bilinear Bäcklund transformation for this equation, mapping N-soliton solutions on (N+1)-soliton solutions. Our analysis extends the results previously obtained by Hirota for the Classical Boussinesq system to actual (c≠ 0) “pq=c”-reductions performed on Wronskians.
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Masato Hisakado, Miki Wadati
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
389-393
Published: February 01, 1996
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The discrete surfaces (triangulate surfaces) in 3-dimensional spaceare mapped to the sphere S
2 and differential-difference equations are obtained to describe the motion of the discrete surfaces on the S
2. These equations contain integrable dynamics such as the discrete nonlinear Schrödinger equation and the discrete complex mKdV equation. Relations between the motion of discrete surfaces and nonlinear integrable differential-difference equations are discussed.
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Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
394-401
Published: February 01, 1996
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The integrable quantum many-body systems associated withthe classical root systems are formulated in terms of the(trigonometric) Dunkl operators.We define the Dunkl operators by use of the infinite-dimensionalrepresentation of the R and K matrices for the Yang-Baxterequation and the reflection equation.The eigenvalues of systems are also given.
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Yoshihiko Nonomura
Subject area: Statistical physics and thermodynamics.
1996 Volume 65 Issue 2 Pages
402-406
Published: February 01, 1996
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The two-dimensional S=1/2 asymmetric Heisenberg Mattis model is investigated with the exact diagonalization of finite clusters. The Néel order parameter and the spin glass order parameter can be smoothly extrapolated to the thermodynamic limit in the antiferromagnetic region, as in the pure Heisenberg antiferromagnet. The critical concentration of the Néel phase is consistent with that of the two-dimensional Ising Mattis model, and the spin glass order parameter increases monotonously as the ferro-bond concentration increases. These facts suggest that quantum fluctuation does not play an essential role in two-dimensional non-frustrated random spin systems.
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A. Maghari, M. Najafi
Subject area: Statistical physics and thermodynamics.
1996 Volume 65 Issue 2 Pages
407-410
Published: February 01, 1996
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An inversion procedure has been used to obtain, from the extended principle of corresponding states, the intermolecular potential energy functions for Ne-Ar, Ne-Kr, and Ne-Xe over a range of reduced temperature extending from 0.3 to 100. These directly determined potentials are in good agreement with the HFD-B potentials proposed by Barrow et al.
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Noboru Hashimoto
Subject area: Specific reactions and phenomenology.
1996 Volume 65 Issue 2 Pages
411-414
Published: February 01, 1996
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The observed rapidity distribution of particles from diffractive state X in \=pp→ \=pX is asymmetric with respect to the kinematic central value \bar{y}=ln(√{s}/M) of the system X, where √{s} and M are c.m.s. energy and invariant mass of X, respectively. In the framework of the geometric quark jet model, this asymmetry suggests existence of a leading particle in fragmentation of diffractively excited states.
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A. M. Harun ar Rashid, S. M. Khairul Alam
Subject area: Specific reactions and phenomenology.
1996 Volume 65 Issue 2 Pages
415-420
Published: February 01, 1996
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The Standard Model prescribes a definite Lagrangian for the coupling of the W-boson to the photon. Measuring the coupling constant will test an important ingredient of the Model i.e., the verification of non-Abelian gauge structure of the Standard Model. Using the process eγ → Wν we study the most general C and P conserving vertex in e
+e
- collisions at a future 500GeV collider. This vertex contains two parameters, the anomalous magnetic moment κ and the quadrupole moment λ . For the process eγ → Wν we present analytical expressions for the differential cross-section for arbitrary values of κ and λ which explicitly demonstrate the presence of a zero at u=0 in the Standard Model.
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Kyozaburo Takeda, Kenji Shiraishi
Subject area: Electronic structure of atoms and molecules: theory.
1996 Volume 65 Issue 2 Pages
421-438
Published: February 01, 1996
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Electronic structures of polypeptide chains are theoretically studied.To extract the electronic tendency and/or electronic functions of individualamino acids, twelve kinds of homopolypeptide chains, which are formed bya single kind of amino acids, are considered, and their electronic structuresare investigated by the first-principle band calculation. Polypeptide chains have the potential to be a semiconductor havinga wide band gap of 3 -- 5 eV. Their band-edge states are basically theπ electronic states and can delocalize along the peptide backbone. Thedegree of the delocalization depends on the kind of constituent amino acidsand also the orientation of the amino acid side chains against the peptidebackbone. We also investigate how the random alignment of amino acids affectsthe band-edge electronic structures by using the coherent potential approximationapproach. In accordance with the kind of aligned amino acids, the aperiodicityin the alignment produces amalgamated electronic states so as to annihilatethe individual amino acid's electronic identity, or produces persistentstates in order to maintain their electronic characteristics.
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Akihiro Ishizawa
Subject area: Fluid dynamics.
1996 Volume 65 Issue 2 Pages
439-449
Published: February 01, 1996
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The vorticity evolution induced by a source doublet that turns out in a two-dimensional shear flow is investigated analytically for an incompressible inviscid fluid.The velocity field is obtained by use of the linearized Euler equation and the equation of continuity. The process of the closed vortex formation around the doublet and the interaction of these closed vortex are shown by investigating the time development of the disturbance vorticity.
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Hideaki Miura
Subject area: Fluid dynamics.
1996 Volume 65 Issue 2 Pages
450-461
Published: February 01, 1996
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A mechanism of enstrophy generation is investigated numerically in ashock-dominated turbulence driven by a random external force which hasonly the compressible component.Enstrophy is generated, especially on collision of shock, as a pairof vortex tube of opposite sense of rotation behind curved shocks.The roles of various terms in enstrophy equation are clarified inenstrophy generation process.Generation of enstrophy is enhanced by strong alignment of eachterm of the enstrophy equation with the vorticity vector.
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In–Sung Jang, Shinsuke Watanabe
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1996 Volume 65 Issue 2 Pages
462-467
Published: February 01, 1996
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The formation process of a vortex ring by an exploding wire in water is investigated experimentally. The formation of a vortex ring has been assumed to be related to the water flow induced by an exploding wire (S. Watanabe et al.: J. Phys. Soc. Jpn. 64 (1995) 3748). This assumption is examined experimentally. As soon as a wire explodes in a pipe with one outlet, a vapor bubble starts to grow around the electrodes and then performs a damped oscillation. The radius of a bubble is observed to reach its first maximum at 3.5-- 5.0ms after the explosion. The formation of a vortex ring at the outlet of a pipe is confirmed to begin at 0.35ms after the explosion and to end at 2.0ms. These two observations lead us to conclude that the formation of a vortex ring originates from a high speed flow of water generated by an expanding vapor bubble of an exploding wire.
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Kimitaka Itoh, Sanae–I. Itoh
Subject area: The physics of plasmas and electric discharges.
1996 Volume 65 Issue 2 Pages
468-471
Published: February 01, 1996
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Heat pinch phenomena in the plasma with peripheral heating is discussed from the view point of thermodynamics. The entropy production rate associated with inward energy flow in the presence of energy exchange between electrons and ions is calculated. The inward energy flow can increase the total entropy production rate. It is conjectured that the outward energy flow of colder species (say ions) could sustain the energy flux of hotter species (say electrons) in the core, which flows into the direction of higher temperature.
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Akira Nohara
Subject area: Mechanical and acoustical properties of condesed matter.
1996 Volume 65 Issue 2 Pages
472-475
Published: February 01, 1996
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A variational principle is proposed for the energy dissipation rate in two deformation modes in alloy-type Al--Mg solid solutions at high temperatures. For constant-stress creep the principle leads to the steady-creep law and a partial differential equation for the net dislocation-multiplication rate in nonsteady state. The solution to this equation gives the time development of dislocation density, from which the time development of creep strain is obtained. Fitting a theoretical creep strain vs time curve to an experimental one allows us to determine the relaxation time of creep and provides a method of measuring the average energy of a dislocation. For constant-strain-rate deformation, on the other hand, the principle leads to the steady-deformation law and another partial differential equation for the net dislocation-multiplication rate in nonsteady state. On the basis of the solution to this equation, a stress vs strain relation is obtained.
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Naritosi Kawamura, Ken Kajiwara, Kenji Fukushima
Subject area: Lattice dynamics and crystal statistics.
1996 Volume 65 Issue 2 Pages
476-481
Published: February 01, 1996
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The purpose of this article lies in a qualitative understanding of the vibrational excitation of C
60 molecule. In this paper we look upon a C
60 molecule as a 2-dimensional lattice with the icosahedral symmetry and then start with the analysis ofthe infinitesimal oscillation of a spherical elastic membrane, i.e., a 2-dimensional version of the Debye model. The analysis of the model turns out to be successfully carried out on a basis of the Riemannian geometry. We next approximate the vibration of C
60 molecule by that of a spherical membrane partially discretized in an icosahedral-symmetric way. The whole process described is expected to help understand a qualitative aspect of the existing results of the computer simulation. Finally it may be noteworthy that the method here developed is easily applicable to a variety of fullerenes.
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Tsutomu Sato, Jun Suda
Subject area: Lattice dynamics and crystal statistics.
1996 Volume 65 Issue 2 Pages
482-488
Published: February 01, 1996
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The first-order Raman spectra of A
1g and B
1g mode in aragonite crystal were measured in the temperature range of 4.4-- 630, K and the linewidths at these temperature were obtained. The temperature dependence of the linewidths was analyzed by the phonon dispersion curves based on the Born-von Karman model, and the results showed that it was caused approximately by the cubic anharmonic term in crystal potential energy.
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Hironori Sakamoto, Tatsuki Oda, Masafumi Shirai, Naoshi Suzuki
Subject area: Lattice dynamics and crystal statistics.
1996 Volume 65 Issue 2 Pages
489-495
Published: February 01, 1996
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First-principles frozen-phonon calculations based on the full-potential linearized augmented-plane-wave method are performed for the X point phonon modes of the high-pressure FCC phase of solid iodine. The longitudinal and the transverse phonon frequencies have been evaluated to be ω
L=231 cm
-1 and ω
T=159 cm
-1, respectively, at 45 GPa. The phonon frequencies increase with increasing pressure, i.e. ω
L=260 cm
-1 and ω
T=179 cm
-1 at 64 GPa. The phonon frequencies in the whole Brillouin zone are calculated by expressing the dynamical matrix as the sum of χ and D
0: the generalized electronic susceptibility χ is evaluated by utilizing the electron-phonon interaction obtained microscopically on the basis of the tight-binding scheme and the short-range force term D
0 is determined so as to reproduce the X point phonon frequencies obtained by the frozen-phonon method. Pressure effects on the superconductivity of FCC iodine are discussed by using the obtained results.
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Makoto Iwata, Sadamitsu Harada, Yoshihiro Ishibashi
Subject area: Equations of state, phase equilibria, and phase transitions.
1996 Volume 65 Issue 2 Pages
496-498
Published: February 01, 1996
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Temperature dependences of diagonal elements of the elastic stiffness constant in [N(CH
3)
4]
2ZnI
4 single crystal have been measured between room temperature and about 200K by means of the ultrasonic pulse echo overlap method. In the room temperature phase (phase I), softening of the elastic constant c
55 has been observed. The transition temperature has been determined to be T
C1=256K. The second elastic anomaly of phase transition has been observed at T
C2=213K.
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Kee–Kahb Koo
Subject area: Transport properties of condensed matter (nonelectronic).
1996 Volume 65 Issue 2 Pages
499-504
Published: February 01, 1996
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A comparison of dendritic growth kinetics of various materials with the transport theories suggests that dendritic growth kinetics of materials might be dependent on microstructure of crystals. Also advective flow created during solidification seems to be taken into account when the growth kinetics of dendrites is determined, which has not been considered before. A plot of stability parameters, σ
*, of different anisotropic materials as a function of anisotropy of interfacial energy, ε
m, indicates that relationship σ
*-- ε
m7/4 does not hold, which is the main prediction of microscopic solvability theory. This fact suggests that stability parameter seems to be determined not only by anisotropy of given material but also other factors which is not yet found.
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Hiroshi Ajiki, Tsuneya Ando
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 2 Pages
505-514
Published: February 01, 1996
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Electronic states of carbon nanotubes in a magnetic field perpendicular to the axis are studied in a tight-binding model and the validity of k·p theory is examined.The energy bands near the Fermi level calculated in the tight-binding model agree with those of k·p in a wide magnetic-field range except in extremely high fields where the flux passing through the unit cell of a two-dimensional graphite is comparable to the flux quantum, i.e. up to --4000 T.A slight deviation from the k·p result in weak magnetic fields can be explained by the inclusion of higher order terms in the k·p expansion leading to trigonal warping of bands.
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Masahiro Takashita, Haruyoshi Aoki, Taichi Terashima, Shinya Uji, Kuni ...
Subject area: Electron states in condensed matter.
1996 Volume 65 Issue 2 Pages
515-524
Published: February 01, 1996
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We have performed an extensive dHvA effect study of CeRu
2Si
2 to gain more insight into the nature of the metamagnetic transition. The angular dependence of the dHvA frequencies confirms the transition of the Fermi surfaces from those of the itinerant f electron below the metamagnetic transition field (H
m) to those of the localized f electron above H
m. The field dependence of the frequencies and effective masses are measured for all the frequencies observed with fields parallel to [001]. A waveform analysis suggests that the Fermi surfaces of the up and down spin electrons are similar in size, whereas the effective masses are significantly different. The amplitudes of the dHvA oscillations and their field dependence are anomalous above H
m, implying that the dHvA oscillations above H
m may possibly come from a state which is not well developed near H
m.
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Isao Sawada, Junichi Okada, Yoshihiro Kuroda
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 2 Pages
525-528
Published: February 01, 1996
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The present authors have obtained a closed-form solution to the Mori formula for transport coefficients expanded in terms of the projection operator most recently. The present article supplements the previous work by confirming the equivalence between the Mori formula and the Kubo formula unambiguously through evaluating the optical conductivity for a free two-band model explicitly.
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Masahito Takahashi, Yasuhiro Hatsugai, Mahito Kohmoto
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 2 Pages
529-537
Published: February 01, 1996
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We consider conductivities of two-dimensional lattice electrons in a magnetic field.We focus on systems where the flux per plaquette φ is irrational (incommensurate flux). To realize the system with the incommensurate flux, we consider a series of systems with commensurate fluxes which converge tothe irrational value. We have calculated a real part of the longitudinal conductivity σ
xx(ω).Using a scaling analysis, we have found \Reσ
xx(ω)behaves as 1/ω
γ, (γ =0.55) when φ =τ, (τ =\frac{√{5}-1}{2}) and the Fermi energy is near zero.This behavior is closely related to the known scaling behavior of the spectrum.
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Makoto Inokuchi, Hiroyuki Tajima, Toshiaki Ohta, Haruo Kuroda, Akiko K ...
Subject area: Electronic transport in condensed matter.
1996 Volume 65 Issue 2 Pages
538-544
Published: February 01, 1996
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Electrical resistivity under a high pressure and the upper critical magnetic field (H
c2) in the superconducting state were investigated on the ambient-pressure superconductor α -(EDT-TTF)[Ni(dmit)
2], which exhibits a phase transition around 20K and the superconducting transition at 1.3K under ambient pressure. Above 9.9, kbar, the superconducting transition was not observed down to 0.5K, while the former transition survived up to 13.7kbar. The temperature dependence of H
c2 was estimated: |dH
c2/dT|_{T=T
c} ≈ -0.27T/K (Bparallel c
*-axis); |dH
c2/dT|_{T=T
c} ≈ -3.5T/K (B// ab-plane). The anisotropy of H
c2 within the ab-plane was found to be quite small indicating the two-dimensionally isotropic character within the ab-plane in the superconducting state of the salt.
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Nobuyuki Ogawa, Manfred Sigrist, Kazuo Ueda
Subject area: Superconductivity.
1996 Volume 65 Issue 2 Pages
545-551
Published: February 01, 1996
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The vortex structure of an unconventional superconductor in a thinfilm is investigated using the example of a two-components orderparameter. Under certain conditions such vortices do not posses a normal core. In this case, our theory shows an anomaly in the H
c1 (for fields paralle to the film) as a function oftemperature or film thickness. The origin of this anomaly lies in structural transition of the vortex which leads to thestabilization of fractional vortices in the film.
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Minoru Hamada, Hiroshi Shimahara
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
552-559
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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We study the magnetic ground state of a generalized Kondo lattice model with classical localized spins, which includes antiferromagnetic exchange interaction J between localized spins. We determine the magnetic phase diagram on the plane of J and fermion concentration n, examining all possibilities of planar order of the localized spins in two dimensions. We find canted ferromagnetic phases, diagonal spiral phases, stripe spiral phases as well as the Néel ordered phase and the ordinary ferromagnetic phase. The densities of states of the fermions for these localized spin state are calculated. For small n, we analytically examined the stability of the Néel state and the ferromagnetic state in detail in any dimensions. We also discuss the t-J limit, J
K/t → ∞, for small n.
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Yoshihiro Nishiyama, Naomichi Hatano, Masuo Suzuki
Subject area: Mathematical methods in physics.
1996 Volume 65 Issue 2 Pages
560-568
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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The ground state of the four-chain Heisenberg ladder model is numerically investigated. Hidden-order correlations suitable for the system are introduced and calculated with an emphasis on the spatially isotropic point, where a corresponding material exists.The existence of a long-range hidden-order correlation indicates formation of a short-range RVB state in the case of the antiferromagneticinter-chain coupling.A transition between the phase of the ferromagnetic inter-chain couplingand that of the antiferromagnetic one is discussed.
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Yoshiyuki Fukumoto
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
569-580
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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We investigate the effects of the XY-like anisotropy on thermodynamic quantities of the two-dimensional XXZ model on the square lattice using a Schwinger boson mean-field approach. Our formulation leads to correct relations of the spin correlation functions; ‹ S
ixS
jx› =‹ S
iyS
jy› ≠ ‹ S
izS
jz› . The internal energy, specific heat, spin correlation functions, uniform susceptibilities and correlation length are obtained after we correct the transverse spin correlation function by an extra factor 1/2. At zero temperature our results agree with those of the conventional spin wave theory and those of numerical studies. At low temperatures thermal quantities, except for the transverse susceptibility for the ferromagnetic XXZ model and the correlation length, agree with those of numerical studies. In particular, we find that the transverse uniform susceptibility of the antiferromagnetic XXZ model behaves as a+bT
3 at low temperatures in contrast to the T-linear behavior of the isotropic Heisenberg antiferromagnet.
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Shuichi Wakimoto, Chul–Ho Lee, Kazuyoshi Yamada, Yasuo Endoh, Sy ...
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
581-585
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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Systematic heat treatments have been performed using single crystals of La
2-xBi
xCuO
4+δ to study the effect of oxygen doping on the phase stability as well as the three-dimensional magnetic order. For La
2CuO
4+δ, the analysis of magnetic susceptibility peak near the Neel temperature T
N revealed that the continuous decrease of T
N upon doping is terminated at 280K. The further doping additionally induces the previously reported macroscopic phase separation accompanying an antiferromagnetic phase with T
N=265K and a superconducting one with T
C≤ 35K. On the other hand, for La
2-xBi
xCuO
4+δ with x-- 0.05 no macroscopic phase separation was observed up to δ ≈ 0.02. Upon the oxygen doping, the T
N continuously decreases from 310K to below 10K only by the heat treatment. The scaling behavior of magnetic ssusceptibility previously studied by the powder sample of La
2-xSrxCuO
4+δ was reexamined in this system.
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Kunitomo Hirai
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
586-593
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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The difference between sinusoidal and helical spin density wave states is discussed in reference to these states of chromium and fcc iron. The relative stability between these states against the magnitude of local magnetic moments is investigated. It is shown that for chromium the stable spin density wave state changes from a sinusoidal one to a helical one as the magnitude of local magnetic moments becomes large while for fcc iron the stable spin density wave state is always a helical one. The effect of charge modulation associated with sinusoidal spin density wave on the stability is further investigated. It is shown that the charge modulation stabilizes the sinusoidal spin density wave state. The difference in electronic structure between sinusoidal and helical spin density wave states is also elucidated.
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Kazuo Hida
Subject area: Magnetic properties and materials.
1996 Volume 65 Issue 2 Pages
594-600
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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The ground state of the square lattice bilayer quantum antiferromagnet with nearest and next-nearest neighbour intralayer interaction is studied by means of the modified spin wave method. For weak interlayer coupling, the ground state is found to be always magnetically ordered while the quantum disordered phase appear for large enough interlayer coupling. The properties of the disordered phase vary according to the strength of the frustration. In the regime of weak frustration, the disordered ground state is an almost uncorrelated assembly of interlayer dimers, while in the strongly frustrated regime the quantum spin liquid phase which has considerable Néel type short range order appears. The behavior of the sublattice magnetization and spin-spin correlation length in each phase is discussed.
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Kenzo Naito
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
601-605
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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Detailed spectra of core electron (5s, 5p) resonant photoemission on RCu
6 (R=La, Ce, Pr) have been measured. It is found that the excitation spectra of the Auger electron yield well explains the high energy region of the 4d-4f giant resonance band. A double peak structure, corresponding to the multiplet, of excitation spectrum of the valence band is observed on PrCu
6.
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Masami Fujita, Kazunori Hayakawa, Kazutoshi Fukui, Mamoru Kitaura, Hid ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
606-609
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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The polarized reflectivity spectra of monoclinic SnI
2 crystals were measured at 13K for polarization parallel and perpendicular to the crystal b-axis. The direct exciton band was found at 2.57eV. The dichroism of the exciton band indicates a strong axial crystal field along the b-axis.The exciton transition is discussed in terms of the cationic 5s→ 5p excitation in Sn
2+ ions. The fundamental absorption tail was measured at various temperatures. The Urbach rule holds for the tail. The high temperature steepness parameter σ
0=0.70 indicates the strong exciton-phonon coupling in SnI
2 crystals.
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Eiichi Tsuji, Takahiro Kurasawa, Ichiro Yazawa, Hiroyuki Katoh, Nobuyu ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
610-614
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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X-ray polarization analyses were carried out for allowed and forbidden (00l) reflections as well as a magnetic scattered satellite peak of a hexagonal ferrite (Ba
1-xSr
x)
2Zn
2Fe
12O
22 using synchrotron radiation. Polarization mixing was observed in both forbidden reflections and the magnetic scattered satellite peak. Magnitudes of the components of the structure factor tensor for the forbidden reflection are determined.
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Arata Tanaka, Takeo Jo
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
615-621
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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We analyze the recently measured resonant inverse photoemission spectroscopy (IPES) at the Ce 3d threshold in CeNi
2 and CeRh
3, which corresponds to a superposition of 4f
n → 3d
94f
n+2 → 4f
n+1 processes with n = 0 and 1, and predict an expected resonant IPES in CeO
2 on the basis of the Anderson impurity model including the full multiplet effect. By discussing a difference in selection rule of the final state between off- and on-resonances, the observed difference in spectrum is interpreted. The analysis shows that the magnitude of 4f-ligand hopping integral connecting the 4f
2 and 4f
3 configurations with a 3d core hole is to be reduced to -- 1/3 for CeNi
2 and -- 1/2 for CeRh
3 of that connecting the 4f
0 and 4f
1 configurations without the core hole, which dominantly determines the 4f ground state. A tentative calculation assuming the reduction of -- 0.8 is performed for CeO
2. The calculation is also extended to IPES at the 4d core thrshold for CeNi
2.
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Hideyuki Ohtake, Koichiro Tanaka, Takeyo Tsukamoto, Toru Suemoto
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1996 Volume 65 Issue 2 Pages
622-626
Published: February 01, 1996
Released on J-STAGE: October 01, 1999
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We measured electronic Raman scattering originating from photoexcited L valley electrons in undoped, p-type (N
h=10
17 cm
-3), and n-type (N
e=10
17 cm
-3) germanium crystals at lattice temperature from RT to 76 K when stimulated by 1.58-eV laser light. From analysis of the power dependence of Raman intensity in the three samples and comparison of the spectral shape with reported data onheavily doped n-type crystal, the origin of this scattering is ascribed to electrons in the L valley. We analyzed this Raman scattering by using Ipatova'stheory, and found that phononassisted intervalley scattering was dominant in the temperaturedependence of the width (FWHM of modified Lorentzian) of the electronic Raman scattering spectra.We also succeeded in reproducing the temperature dependence ofscattering intensity taking into account the temperature dependentdiffusion constant of electrons.
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