-
Satoshi Yukawa, Macoto Kikuchi, Gen Tatara, Hiroshi Matsukawa
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 10 Pages
2953-2956
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The concept of thermal ratchets is extended to the system governed by quantum mechanics. We study a tight-binding model with an asymmetric periodic potential contacting with a heat bath under an external oscillating field as a specific example of quantum ratchet. The dynamics of a density operator of this system are studied numerically using the quantum Liouville equation. The finite net current is found in the nonequilibrium steady state, which originates from purely quantum mechanical effects. The direction of the current varies with parameters, in contrast with the classical thermal ratchets.
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Matthias Troyer, Masatoshi Imada, Kazuo Ueda
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 10 Pages
2957-2960
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We have performed a large scale quantum Monte Carlo study of the quantum phase transition in a planar spin-1/2 Heisenberg antiferromagnet with CaV
4O
9 structure. We obtain a dynamical exponent z=1.018±0.02, consistent with Lorentz invariance. The critical exponents β, ν and η agree within our errors with the classical 3D O(3) exponents, expected from mapping to the nonlinear sigma model.
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Iwao Hosokawa, Shin–ichi Oide, Kiyoshi Yamamoto
Subject area: Fluid dynamics.
1997 Volume 66 Issue 10 Pages
2961-2964
Published: October 01, 1997
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Vortical structure in decaying isotropic turbulence is studied by direct numerical simulation on the 512
3 grid. At the fully-developed state, while it is well-known that many tubes with high vorticity which may be called “worms” are created throughout the space, we have found that the background vorticity field is never random but is so coherent that it involves many tubes with much lower vorticity cores than the former, that may be called “soft worms”, in some cases much thicker and longer than the former tubes. It is debated that the similitude of all hard and soft tubes with the Burgers vortices may be acknowledged only in a certain average sense.
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Sumio Ishihara, Satoshi Okamoto, Sadamichi Maekawa
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
2965-2968
Published: October 01, 1997
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Pressure effects on the charge and spin dynamics in the bilayer manganite compounds La
2-2xSr
1+2xMn
2O
7 are studied theoretically by taking into account the orbital degrees of freedom. The orbital degrees are active in the layered crystal structure, and applied hydrostatic pressure stabilizes the 3d
x2-y2 orbital in comparison with 3d
3z2-r2. The change of the orbital states weakens the interlayer charge and spin couplings, and suppresses the three dimensional ferromagnetic transition. Numerical results, based on an effective Hamiltonian which includes the energy level difference of the orbitals, show that the applied pressure controls the dimensionality of the spin and charge dynamics through changes of the orbital states.
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Keita Kishigi, Kazushige Machida, Yasumasa Hasegawa
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
2969-2972
Published: October 01, 1997
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Stimulated by a recent experiment on (TMTSF)
2ClO
4, reporting a new phase diagram with a first order transition line at the high field, the field induced spin density wave (FISDW) states are reexamined under the anion ordering. It is found that a new type of FISDW state, which differs from that described by the so-called standard theory, is stabilized. We interpret the first order line as arising from a transition between the new state and the standard one when H is varied.
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Takeshi Nakanishi, Tsuneya Ando
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
2973-2976
Published: October 01, 1997
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The conductance of a junction connecting two carbon nanotubes of differing diameter is calculated in magnetic fields perpendicular to the tube axis. The relative importance of mixing between different valleys exhibits a characteristic change depending on the effective strength of the magnetic field in the two tubes. The conductance depends only on the component of the magnetic field in the direction of the pentagonal and heptagonal rings.
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Yositake Takane, Katsuhiro Nakamura
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
2977-2980
Published: October 01, 1997
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The ballistic weak-localization (WL) effect in chaotic billiards is studied using an extended semiclassical approximation. We show that diffraction-induced partially time-reversed pairs of paths are essential to describe the WL effect. By incorporating such pairs, we obtain the WL correction to both the transmission and reflection coefficients, which satisfies the unitarity. This result provides an answer for the puzzle addressed by Baranger et al. [Phys. Rev. Lett. 70 (1993) 3876] that the WL correction arises only in the reflection coefficient but not in the transmission coefficient so long as the usual semiclassical approximation is employed. We also find the full expression of the WL correction in the presence of a weak magnetic field.
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Noriaki Sato, Naofumi Aso, Gerry H. Lander, Bertrand Roessli, Takemi K ...
Subject area: Superconductivity.
1997 Volume 66 Issue 10 Pages
2981-2984
Published: October 01, 1997
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UPd_2Al_3 is an itinerant antiferromagnet (T
N = 14.3 K) coexisting with the superconducting state (T
c {--} 2 K). We have performed neutron inelastic scattering experiments at T = 10 and 20 K. The spectra have been found to be described in energy by a single Lorentzian function and analyzed on the basis of the so called self-consistent renormalization (SCR) theory. We determined the characteristic energy scale, T
0 {--} 27 K, which represents the energy spread of the spin fluctuations. We have obtained the direct experimental evidence that the same proportionality relation between T
0 and T
c holds in UPd_2Al_3 as observed in high-T
c cuprates, strongly suggesting that the superconductivity in UPd_2Al_3 is mediated by the spin fluctuations.
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Wataru Koshibae, Yuhki awamura, Jun–ichiro Inoue, Sadamichi Maek ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
2985-2988
Published: October 01, 1997
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In manganites, the spin ordering depends on the orbitals in the e_g state of Mn ions. It is shown that the magnetization process is also strongly affected by the orbitals, by using the exact diagonalization technique applied to the effective Hamiltonian which includes a coupling between the spin and orbital degrees of freedom derived from strong on-site Coulomb interaction and orbital degeneracy of Mn ions. We find that the spin moment induced by an applied magnetic field is accompanied with the change of the orbital structure. Such a coupling between the spin and orbital degrees of freedom results in a charasteristic magnetization process of manganites. Recent experimental data obtained in Pr
0.5Ca
0.5MnO
3 and related compounds are examined in the light of the present theory.
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Hirotaka Manaka, Isao Yamada, Takahiro Kitazawa, Michihiro Kobayashi, ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
2989-2992
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Since the ferromagnetic intralayer exchange interaction in K
2CuF
4 is due to the antiferrodistortive (AFD) orbital ordering of the 3d holes of Cu
2+ ions, we expect that the ferromagnetism of this compound to disappear when the AFD order of the distortion of CuF
6 octahedra collapses. Recent magnetic susceptibility measurements performed at high pressures on this compound actually confirmed the disappearance of the ferromagnetism above approximately 9 GPa [M. Ishizuka et al.: J. Phys. Soc. Jpn. 65 (1996) 1927]. To obtain evidence of the pressure-induced structural change which corresponds to the magnetic change mentioned above, we measured the pressure dependence of the phonon-Raman spectra of this compound. As a result, we found that the scattering lines relevant to the vibrational modes of CuF
6 octahedra ordered in the AFD fashion disappeared above 9-- 10 GPa. This result is consistent with the structure above 9 GPa revealed by recent X-ray diffraction experiments that we performed.
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Yuji Aoki, Jun Urakawa, Hitoshi Sugawara, Hideyuki Sato, Tadashi Fukuh ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
2993-2996
Published: October 01, 1997
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To investigate the non-Fermi liquid (NFL) behavior in a nonalloyed system CeNi
2Ge
2, we have measured the temperature and field dependences of the specific heat C on a CeNi
2Ge
2 single crystal. The distinctive temperature dependence of C/T (--α-β√T) is destroyed in almost the same manner for both field directions of B//c-axis and B//a-axis. The overall behavior of C(T,B) and the low-temperature upturn in χ(T) can be reproduced, assuming an anomalous peak of the quasi-particle-band density-of-states (DOS) at the Fermi energy possessing √ε energy dependence. Absence of residual entropy around T=0 K in B -- 0 T has been confirmed by the magnetocaloric effect measurements, which are consistent with the present model. The present model can also be applied to the NFL behavior in CeCu
5.9Au
0.1 using a ln(ε)-dependent peak in the DOS. Possible origins of the peak in the DOS are discussed.
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Hiroki Nakano, Masayuki Hagiwara, Teiji Chihara, Minoru Takahashi
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
2997-3000
Published: October 01, 1997
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One-dimensional S=1 spin systems with bond alternation (J
1 and J
2) and single-ion anisotropy (D
z) are studied. We numerically diagonalize the Hamiltonians of finite size up to ten spins and calculate the temperature dependence of the susceptibility. The theoretical curves are applied to analyze the susceptibilities of {Ni
2(EDTA)(H
2O)
4}
n·(2H
2O)
n (EDTA= ethylenediaminetetraacetic acid) and [ {Ni
2(Medpt)
2(μ-ox)(μ-N
3)}
n](ClO
4)
n (Medpt=methyl-bis(3-aminopropyl)amine). The estimated results of J
2/J
1=0.26, D
z/J
1=0.17, (J
1 -- 13 K) for {Ni
2(EDTA)(H
2O)
4}
n·(2H
2O)
n and J
2/J
1=0.30, D
z/J
1=0.07, (J
1 -- 43 K) for [ {Ni
2(Medpt)
2(μ-ox)(μ-N
3)}
n](ClO
4)
n are presented. We find that both are systems with the singlet-dimer ground state.
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Katsurou Hanzawa, Keiichi Ohara, Kei Yosida
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
3001-3004
Published: October 01, 1997
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We calculate the magnetization as a function of magnetic field in the mean-field approximation for the periodic Coqblin-Schrieffer model. Prior to a metamagnetic second-order transition from heavy-fermion to local-moment state, a rapid increase in the magnetization, which resembles the metamagnetic-like behavior in {CeRu
2Si
2}, appears if the anisotropy of the hybridization matrix element is taken into account.
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Osamu Sakai, Ryousuke Shiina, Hiroyuki Shiba, Peter Thalmeier
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
3005-3007
Published: October 01, 1997
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The hyperfine coupling between the multipolar moments of the Ce ion and the nucleus of B ion is discussed phenomenologically for the antiferro-quadrupolar ordering (AFQ) phase of CeB
6. The longstanding mutual inconsistency between neutron diffraction and NMR in phase II can be resolved by considering the induced octupolar moment with the T
xyz type. The experimental facts indicate that the AFQ of the Γ
5+ symmetry (i.e. O
xy, O
yz and O
zx types) is realized in CeB
6.
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Tetsuo Ohama, Hiroshi Yasuoka, Masahiko Isobe, Yutaka Ueda
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1997 Volume 66 Issue 10 Pages
3008-3011
Published: October 01, 1997
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51V NMR measurements in the uniform state of NaV
2O
5 are presented. The NMR shift and the electrical field gradient (EFG) were measured at the tetravalent V sites. Observed anisotropy of the NMR shift and the EFG indicates that the d
xy-like orbital is occupied. It has been found that the orbital susceptibility in the uniform state is significantly smaller than the residual susceptibility in the spin-Peierls state. The possible origins of this disagreement are discussed.
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Rei Inoue, Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 10 Pages
3013-3020
Published: October 01, 1997
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Studied is the discrete analogue of the classical W
N algebra. We derive a new representation of the exchange algebra. We discuss in detail a construction of the currents of the lattice W
3 algebra.
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Yasumasa Kajinaga, Miki Wadati
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 10 Pages
3021-3025
Published: October 01, 1997
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New boundary conditions of the so-called ``modified Volterra model'', which is described by a set of the nonlinear differential-difference equations, are presented. In accordance with the methods developed by Sklyanin, these conditions are shown to be integrable, including the simply truncated open-end case.
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Robert F. Bordley
Subject area: Classical and quantum physics: mechanics and fields.
1997 Volume 66 Issue 10 Pages
3026-3030
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Stochastic mechanics develops a formulation of quantum physics by assuming that a classical particle is also subjected to Brownian-like motion. Because this presumes that a particle's path is non-differentiable, making this transformation often involves implicitly replacing time-derivatives in classical mechanics by finite differences. In this paper, we will develop a stochastic mechanics by explicitly replacing time-derivatives in classical mechanics by finite differences, deriving the resulting dynamics and then introducing stochasticity. Like Nelson's original version of stochastic mechanics, our stochastic mechanics is also consistent with the Schrödinger Equation.
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Takeya Tsurumi, Miki Wadati
Subject area: Classical and quantum physics: mechanics and fields.
1997 Volume 66 Issue 10 Pages
3031-3034
Published: October 01, 1997
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We extend the Zakharov's theory for collapses of Langmuir waves into the system under harmonic potential. As a possible application, we consider the collapse of the Bose-Einstein condensate with attractive interparticle interactions under magnetic trap.
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Takeya Tsurumi, Miki Wadati
Subject area: Classical and quantum physics: mechanics and fields.
1997 Volume 66 Issue 10 Pages
3035-3039
Published: October 01, 1997
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We consider the Bose-Einstein condensate with attractive interparticle interactions (more precisely, negative s-wave scattering lengths) under a magnetic trap. By using a model equation, axially symmetric nonlinear Schrödinger equation with harmonic potential terms, we investigate the time-evolution of the wavefunction. We predict that the collapse of the condensate takes place when the number of atoms exceeds the critical value.
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Tomotoshi Nishino, Kouichi Okunishi
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 10 Pages
3040-3047
Published: October 01, 1997
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We report a real-space renormalization group (RSRG) algorithm, which is formulated through Baxter's corner transfer matrix (CTM), for two-dimensional (d = 2) classical lattice models. The new method performs the renormalization group transformation according to White's density matrix algorithm, so that variational free energies are minimized within a restricted degree of freedom. As a consequence of the renormalization, spin variables on each corner of CTM are replaced by a m-state block spin variable. It is shown that the thermodynamic functions and critical exponents of the q = 2, 3 Potts models can be precisely evaluated by use of the renormalization group method.
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Yuji Hara, Naomichi Hatano, Masuo Suzuki
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 10 Pages
3048-3052
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The F-model (a special case of the six-vertex model) with an impurity is considered, using an exact solution of the six-vertex model. We exactly calculate the energy and the specific heat of the impurity vertex. An additional low-temperature peak is found in the specific heat for impurities that generate frustration.
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Norihiro Tsushima, Yasushi Honda, Tsuyoshi Horiguchi
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 10 Pages
3053-3062
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We investigate a spin-3/2 Ising model on a square lattice by using Monte Carlo (MC) simulations and a density matrix renormalization group (DMRG) method. We obtain phase diagrams of the ground state. We carried out the MC simulations in order to calculate the critical temperature and the critical exponent η. We estimate the critical exponents ν, α and γ by using a finite size scaling analysis. We also calculate the critical temperature, the central charge c and the critical exponent ν by using the DMRG method. From the results obtained by the MC simulations and by the DMRG method, we discuss a universality class of the system. It is found that the values of critical exponents are determined by means of the degeneracy of the ground state. This result suggests that the universality does not hold for the spin-3/2 Ising model. Furthermore we find a possibility of a breakdown of the hyperscaling law. We also confirm that the ferrimagnetic phase exists in a parameter region where the ground state has a fourfold degeneracy, and that a transition between the ferrimagnetic phase and the ferromagnetic phase exists in addition to that between the ferromagnetic phase and the paramagnetic phase.
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Syed Ahmed, Parvin Akther, Nasima Ferdous, Amena Begum, Hiranmay Sen G ...
Subject area: Nuclear reactions and scattering: general.
1997 Volume 66 Issue 10 Pages
3063-3069
Published: October 01, 1997
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Elastic scattering of 65, MeV polarized protons from twenty five nuclei ranging from
16O to
209Bi have been analysed within the framework of the nine parameter optical model. A set of optical model parameters has been obtained which shows the systematic behaviour of the target mass dependence of the real potential, volume integral and the r.m.s. radius. The isotopic spin dependence of the real potential has also been studied. Parameters obtained by fitting the elastic scattering data have been able to reproduce the pickup and stripping reaction cross sections as studied in a few cases.
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Seiji Tsurubuchi
Subject area: Atomic and molecular collision processes and interactions.
1997 Volume 66 Issue 10 Pages
3070-3073
Published: October 01, 1997
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Under a condition of single electron-atom collision, the emission cross sections for 4p→ 4s transitions producing Ar
+ laser emissions were measured with electron impact energies up to 1000 ,eV. It was found that all the transition lines measured showed E
-1 dependence, which suggests that the symmetry forbidden excitation are critical at high energies. The emission cross sections are compared and discussed with reported values, including a newly measured value of the 514.5 ,nm line.
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Ho–Young Kwak, Jung Hee Na
Subject area: Fluid dynamics.
1997 Volume 66 Issue 10 Pages
3074-3083
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Analytic solutions for a sonoluminescing gas bubble have been obtained, which provide density, pressure and temperature distributions for the gas inside bubble oscillating under ultrasonic field. The solutions have revealed that sonoluminescence should occur just prior to the bubble collapse and its duration is less than 300 ,ps and that increase and subsequent rapid decrease in bubble wall acceleration induce the quenching of gas, consequently of the optical emission followed by the substantial temperature rise up to 100,000 ,K, which can be regarded as a thermal spike. Also the solutions have revealed that Guderley's similarity solution is not valid just prior to the bubble collapse. The gas temperature inside the bubble near the collapse is determined primarily by the amount of radiation heat loss. It also turns out that the number of electrons ionized, the ion species and the kinetic energy of electrons affect the spectrum of light emission crucially. The calculated spectral radiance including the significant tails at short wavelengths, which shows a broad maximum, is in good agreement with observed data qualitatively. Further, it has been found that the bulk modulus of the liquid is the most important liquid property for the occurance of single bubble sonoluminescence.
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Jie Zhao, Jun–ichi Sakai, Ryo Shigeta
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1997 Volume 66 Issue 10 Pages
3084-3089
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We numerically calculate anomalous resistivity in electron-positron plasmas with a constant external electric field. The external electric field can accelerate particles to create a runway distribution for electrons and positrons. Due to the counterstreaming of electrons and positrons by the acceleration from the external electric field the Buneman instability with both longitudinal modes and transverse modes is excited. Plasmas are destabilized through wave-particle interaction. The effective collision frequency, which sets the anomalous resistivity, increases proportionally with the drift velocity in the low drift velocity regime. For larger drift velocities the effective collision frequency increases only weakly as further increases in the drift velocity.
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Yasushi Kamimura, Tetsuo Tsutsumi, Eiichi Kuramoto
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3090-3096
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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To clarify `medium' lifetimes of --150 ps in deformed iron, we calculate the positron lifetimes at the core of dislocations and related defects in iron. The calculations are based on an empirical N-body interatomic potential by Finnis and Sinclair for the atomic arrangements and the local-density approximation for the positron--electron correlation. We find the positron lifetime for vacancies associated with edge dislocation to be the medium lifetime, while that for vacancies associated with screw dislocation is almost the same as the single-vacancy value. The positron lifetimes for pure dislocations and for jogged dislocations are close to the perfect-lattice value.
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Kazuhiko Omote, Masatoshi Saito, Yoshio Waseda
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3097-3101
Published: October 01, 1997
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We have proposed a method for calculating the effective pair potentials of molten salt from measured structural data in which a long-range Coulombic interaction is important [K. Omote and Y. Waseda: J. Phys. Soc. Jpn. 66 (1997)]. By applying this method, the effective pair potentials of liquid CuBr have been successfully estimated from the experimental partial structure factors obtained by anomalous X-ray scattering. The resultant potentials show two characteristic features. One is remarkable shielding for the Cu--Cu Coulomb repulsion in its nearest neighbor region. This might be a possible origin for the absence of marked structure in the Cu--Cu correlation and the penetration of Cu ions into the first like-ion coordination shell. The other is the deviation from the Coulomb potential in the range of 0.4-- 0.9 ,nm in the interactions of Cu--Cu and Cu--Br pairs, suggesting a certain correlation to a pre-peak found in the Cu--Cu structure factor at about 10 ,nm
-1.
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Dong–Seok Yang, Seung–Ki Joo
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3102-3106
Published: October 01, 1997
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New formalism of EXAFS analysis for anharmonic system has been applied to anharmonic system of CuBr at temperatures, 150, 300, and 400 ,K. The new formalism gives the consistent results on the second cumulants with a previous work, and the additional constants such as the local thermal expansion coefficient, α
L, force constant, k
0, and anharmonic parameter, β has been derived. The obtained values were α
L=(6.19± 0.05)× 10
-5/K, k
0=(41± 5) ,N/m, and β =(6.0± 0.5)× 10
11 ,N/m
2, respectively, for Br--Cu bond. The higher cumulants were derived in terms of anharmonic parameter, force constant and temperature.
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Tomoko Ohta, Fujio Izumi, Mitsuko Onoda, Masaaki Isobe, Eiji Takayama& ...
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3107-3114
Published: October 01, 1997
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We determined the crystal structure of Ca
13.6Sr
0.4Cu
24+yO
41+z (y=-0.017 and z=-0.035) by a technique of combined neutron and X-ray Rietveld refinement using a superspace group approach. This oxide is a kind of a composite crystal consisting of two interpenetrating subsystems: (a) [(Ca,Sr)
2Cu
2O
3]_∞ containing alkaline-earth metals and spin-½ Heisenberg two-leg ladders and (b) one-dimensional [CuO
2]
∞ chains of CuO
4 squares sharing two opposite edges. The most remarkable structural feature is that parts of Cu1 atoms on the ladder are coordinated to O3 atoms situated in the neighboring [CuO
2]
∞ chains, forming CuO
5 tetragonal pyramids. Cu1 atoms in the CuO
5 pyramids have shorter equatorial Cu1-O bonds than those in CuO
4 squares, which evidences hole doping into the 5-coordinated Cu1 atoms. Modulations are less marked in the [Cu
2O
3]
∞ ladder than In the [CuO
2]
∞ chain owing to the presence of zigzag chains of edge-sharing CuO
4 squares and corner sharing of O2 atoms in the ladder.
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Makoto Yao, Yukinobu Kawakita, Takahiro Shiga, Itsuro Yamamoto, Hirohi ...
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3115-3119
Published: October 01, 1997
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Quasielastic neutron scattering measurements were carried out at room temperature for liquid S
2Cl
2, S
2Br
2, Se
2Cl
2 and Se
2Br
2, which are composed of the molecules having the X-A-A-X type chain unit, X and A being halogen and chalcogen atoms. The measurements were performed at the scattering wave vectors of 0.98, 1.55, 2.32 and 2.66 Å
-1 by using AGNES spectrometer installed in JAERI. By analyzing the intermediate scattering function, which was obtained by Fourier transform of the observed dynamic structure factor, a fast and a slow relaxation processes have been found. The fast process, whose relaxation time is less than 1 picosecond, may be assigned to fluctuations in the dihedral angle within the molecule, while the slow process, whose relaxation time depends strongly on the molecular weight, may be assigned to the translational diffusion of the molecule.
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Masatoshi Saito, Changyong Park, Kazumasa Sugiyama, Yoshio Waseda
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 10 Pages
3120-3126
Published: October 01, 1997
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An apparatus for controlling the glancing angle of incident beam from a synchrotron source has been newly built for structural studies of high temperature liquids by the anomalous X-ray scattering (AXS) method in the reflection mode. The usefulness and capability of this apparatus were demonstrated by obtaining the individual partial structural functions of the liquid Bi
30Ga
70 alloy using the energies close to the Ga K and Bi L
III absorption edges. The data processing for estimating three partials includes the intensity data obtained at the energy of 15.0 ,keV, which is far from both edges and the reverse Monte Carlo (RMC) simulation technique. The resultant partial structural function for Ga--Ga pairs was found to be rather similar to that of pure Ga. On the other hand, partial structural function for Bi--Bi pairs differs from the pure Bi case and the coexistence of more than two species is rather well-recognized in the Bi
30Ga
70 liquid alloy.
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Toshiya Iwai
Subject area: Equations of state, phase equilibria, and phase transitions.
1997 Volume 66 Issue 10 Pages
3127-3133
Published: October 01, 1997
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Ordering processes in a one-dimensional system with quenched impurities and negligible thermal noise for the case of non-conserved order parameter is investigated numerically. We find the following results. (i) For a large impurity density, the average size of a stable domain, l(t), shows a crossover from the growth due to the drift motion, l(t) -- ln t, at the early stage in our simulation to a slowing down of the growth at the late stage. The proportionality coefficient of this logarismic law is a decreasing function of the impurity density. (ii) Scaling property of the domain size distribution function is satisfied for the region of a large size and the scaled distribution function is independent of the impurity density.
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Mariko Higuchi, Takashi Odagaki
Subject area: Transport properties of condensed matter (nonelectronic).
1997 Volume 66 Issue 10 Pages
3134-3138
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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An ideal three-mode model is proposed which consists of two types of stochastic motions, nontrapped and trapped dynamics, and an oscillation to explain the characteristics of the dynamical behavior of supercooled liquids. The intermediate scattering function and the generalized susceptibility are obtained to show this model reproduces the dynamical characteristics of supercooled liquids. The Cole-Cole plot of the susceptibility shows two-semi circles with a shoulder in the negative side of the real axis. The non-Gaussian parameter is shown to have two peaks due to the contribution of the oscillatory motion.
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Hisao Nagasawa, Spiridon Mourikis, Winfried Schülke
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
3139-3146
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The dynamic structure factor S(q, , ω ) of the K-electrons in Li metal was measured in an inelastic X-ray scattering experiment with 0.8 ,eV resolution using synchrotron radiation. The near edge structure of S(q, ,ω ) over an energy range of 30 ,eV from the edge has been obtained for values of qa of 0.22, 0.38, 1.17 and 1.55, where (h/2π) q is the momentum-transfer and a is the K-electron orbital radius. The overall shape of the near edge region changes remarkably with q. On the other hand, the near edge fine structure varies hardly with q and is similar to the soft X-ray absorption near edge fine structure over a wide range of q. This weakly q-dependent fine structure can be attributed to the band structure effecting the final state electron symmetry, while the strongly q-dependent overall shape may be influenced mainly by the initial momentum distribution of the K-electrons.
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Hisashi Shimizu, Masafumi Shirai, Naoshi Suzuki
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
3147-3152
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The electronic, structural and magnetic properties of all transition-metal mononitrides are investigated by FLAPW band calculations. The equilibrium lattice constants estimated for NaCl-type ScN, TiN and VN and for ZnS-type FeN and CoN are in good agreement with the experimental data. The bulk modulus of MN tends to be larger than that of the single fcc crystal phase of the corresponding transition metal. For all MNs the total energy of the NaCl-type structure is lower than that of the ZnS-type structure: for ScN--CrN the energy difference is about 100 mRyd, and for MnN--CuN it is small (<30 mRyd). For MnN, FeN and CoN it is suggested that if their purely bulk samples of NaCl-type are synthesized, the ferromagnetic states may be realized.
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Yasuhisa Tezuka, Shik Shin, Takayuki Uozumi, Akio Kotani
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
3153-3158
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The Ti 2p- and Ti 3p-resonant photoemission studies of Ti
2O
3 were carried out as well as O 1s-resonant photoemission. The Ti 3d band has a broad band width of about 3 ,eV, but the strong resonance enhancement was observed at Ti 3d band just below the Fermi level on the Ti 2p resonance. The enhancement of the doublet Ti 3p main line was observed mainly at the higher binding energy. The resonant enhancements of the satellite structures in the Ti 3d and Ti 3p band regions were also found. The resonance spectra were analyzed by the cluster model calculation with large hybridization energy, where the satellite was elucidated by the charge transfer satellite.
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Ryousuke Shiina, Tomohiro Nishitani, Hiroyuki Shiba
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 10 Pages
3159-3170
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Possible ordered phases in perovskite manganites are investigated in the framework of an effective spin Hamiltonian for the atomic limit. Using the mean-field approximation combined with a group-theoretical consideration, we determine the stable orbital and spin ordered phases at finite temperatures. It is found that the magnetic ordering with low-symmetry spatial arrangement is stabilized due to the mixing interaction between different multipoles. The resulting orbital states are discussed by taking into account the effect of lattice distortion from the cubic symmetry. The spin and orbital states in LaMnO
3 are discussed on the basis of the present theory.
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Tatsuya Okada, Satoru Ohno
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
3171-3177
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Measurements of the electrical conductivity and the thermo-electric power of the liquid M
1-cSe
c (M=Ga, ,In) systems have been extended to the whole composition range. The rapid decrease in conductivity on the M-rich side was similarly found for both liquid systems. In the narrow range of composition where the conductivity minimum frequently occurs, the composition dependence of conductivity for the liquid Ga--Se and In--Se systems exhibited a deep minimum and a small peak, respectively. The thermopower data of liquid Ga--Se and In--Se alloys show a p-n transition at c=0.58 and 0.65, respectively. The conductivity and thermopower of both liquid systems near the stoichiometry were analyzed by using the equations derived from the Kubo-Greenwood formula.
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Mayumi Kato, Akira Endo, Yasuhiro Iye
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
3178-3182
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We have studied the profile of potential modulation introduced to a GaAs/AlGaAs heterostructure two-dimensional electron gas (2DEG) by a striped gold gate with period a=500 nm on the surface. The magnetoresistance oscillation of 2DEG under one-dimensional periodic potential modulation arising from commensurability between the period and cyclotron diameter has been measured as a function of bias voltage applied to the gold gate. The bias alters both the amplitude and lineshape of the potential seen by 2DEG, with concomitant change in the magnetoresistance oscillation. The analysis of the magnetoresistance shows that with a positive bias, the modulation amplitude is considerably reduced and the third harmonic component becomes conspicuous. This suggests that the “built-in” potential modulation, caused mainly by strain resulting from differential contraction between the gold gate and GaAs, has more rectangular landscape, than the potential added by the bias. The strain-induced third harmonic component accounts for the previously unexplained extra dips in the magnetoresistance traces for a magnetically modulated 2DEG with a ferromagnetic metal gate.
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Taro Nagao
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
3183-3187
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Electron transport through square arrays of antidots in a magnetic field is numerically studied for various antidot diameters. Using the linear response theory, we find two features: (1) At the magnetic field of the main peak in the resistivity, there is an optimum antidot diameter at which the conductivity is maximized. (2) In the region of weak magnetic field, negative Hall conductivity is observed. The range of the magnetic field in which the conductivity is negative becomes large when the antidot diameter is increased. Further the origins of the above features are clarified in connection with the classical trajectories of the electron.
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Takahiro Koishi, Yasutomo Arai, Yoshiyuki Shirakawa, Shigeru Tamaki
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
3188-3193
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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By using well-known pairwise potentials, the transport coefficients such as diffusion constant, viscosities and electrical conductivities in molten NaCl have been simulated as a function of temperature. In deriving the conductivity, a nonequilibrium molecular dynamics technique has newly applied and obtained results at several temperatures agree quantitatively with the experimental results. Using the simulated diffusion constants, D_+ and D_-, and the partial electrical conductivities σ_+ and σ_-, deviations from the Nernst-Einstein relation, for positive and negative ions Δ_+ and Δ_-, at several temperatures are also estimated. The average values for Δ_+ and Δ_- are the order of 0.1 and comparable to the experimental result.
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Yukio Yasui, Hisashi Sasaki, Shin–ichi Shamoto, Masatoshi Sato
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 10 Pages
3194-3201
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Transport measurements under the hydrostatic pressure p up to 18.8 kbar have been carried out on single crystals of BaCo
1-xNi
xS
2, which has a layered structure and exhibits the Mott metal-insulator (M-I) transition both with varying x and with applying pressure. Based on resistivity data for x=0.00, 0.05, 0.14 and 0.18, a T-p-x phase diagram of BaCo
1-xNi
xS
2 has been constructed. The phase diagram is similar to that of (V
1-xM
x)
2O
3 (M=Ti and Cr), although the present system does not exhibit clear discontinuity of the transition. Detailed transport behavior observed near the M-I transition induced by the external pressure are presented. For x=0.00, where a large Mott energy gap exists at ambient pressure, the intrinsic critical behavior of the Mott M-I transition seems to be observed, while for the samples with x≠ 0, randomness effects caused by the Ni-substitution for Co seems to be reflected in the critical behavior.
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Takashi Ichinomiya, Kosaku Yamada
Subject area: Superconductivity.
1997 Volume 66 Issue 10 Pages
3202-3210
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We investigate theoretically the temperature dependence of NMR relaxation rate (T
1-1) of (BEDT-TTF)
2Cu[N(CN)
2]Br. In this material T
1-1shows T
3 temperature dependence in superconducting phase, and spin-gap like behavior in normal phase. In the former part of this paper, we concentrate on the superconducting phase and calculate the NMR relaxation rate to determine the symmetry of energy gap. We find that the superconducting gap is d-wave like. In the latter part, we consider the spin fluctuation in the normal state. We derive a relation between resistivity and dynamical susceptibility assuming that the interaction between quasi-particles is mediated by spin-fluctuations. Using this relation, we can explain the sharp decrease of the resistivity as the effect of the spin gap behavior in T
1-1.
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Masashige Matsumoto, Shinichi Kaneko, Nobuhiko Nishida
Subject area: Superconductivity.
1997 Volume 66 Issue 10 Pages
3211-3218
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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Electronic states around a columnar defect in d-wave superconductors are studied within a quasi-classical approximation. It is shown that the local density of states at zero energy has peaks near (1, 1, 0) and (1, 1, 0) direction boundaries of the columnar defect. In contrast to the zero energy the local density of states at the gap (peak) energy is lower near these directions. These properties are qualitatively consistent with an experiment which has been recently performed to study the local electronic structure around a columnar defect in Bi
2Sr
2CaCu
2O
x using scanning tunneling spectroscopy.
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Koichi Kuboya, Kenji Takanaka
Subject area: Superconductivity.
1997 Volume 66 Issue 10 Pages
3219-3223
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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We consider the superlattices consisting of two kinds of dirty type-II superconductors with the different Debye cut-off frequencies and calculate the transition temperature T
c and the upper critical field H
c2. The results show that the effect of the different Debye cut-off frequencies is essentially similar to that of the different BCS coupling constants.
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Makoto Isoda, Yoshinori Takahashi
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
3224-3230
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The stability of antiferromagnetism and the metal-semiconductor transition are investigated in strongly correlated f-electron systems with UNiSn in mind. We introduce an effective Hamiltonian which includes the inter-atomic antiferromagnetic exchange interaction between nearest neighbor f-spins as a result of hybridization between conduction- and localized f-electrons. Based on the model, the phase diagram is investigated with regard to the magnetic and the metal-semiconductor phase transitions. We found the possible stability of the antiferromagnetic state even in the metallic phase, which was already suggested by our previous study using the perturbation expansion in the paramagnetic semiconducting state. The dependence of the Néel temperature on the energy gap is also shown to agree qualitatively with the observed behavior.
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Gregory E. Stewart, Donald D. Betts, James S. Flynn
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
3231-3236
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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First we introduce the upper triangular lattice form method that permits one to derive easily the complete set of finite lattices of any given number, N, of vertices for any regular infinite lattice in any number of dimensions, and we use it to obtain all finite fcc lattices of N<28. We compute the ground state energy, magnetization and spin-spin correlations of the spin one-half XY ferromagnet on each of these lattices. Extrapolation of these data to infinite N yields T=0 estimates of the properties mentioned. Our estimates agree to a few tenths of a percent with spin wave, series expansion and variational estimates.
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Kazuo Hida
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 10 Pages
3237-3241
Published: October 01, 1997
Released on J-STAGE: October 01, 1999
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The effect of dimerization on the random antiferomagnetic Heisenberg chain with spin 1/2 is studied by the density matrix renormalization group method. The ground state energy, the energy gap distribution and the string order parameter are calculated. Using the finite size scaling analysis, the dimerization dependence of the these quantities are obtained. The ground state energy gain due to dimerization behaves as u
a with a > 2 where u denotes the degree of dimerization, suggesting the absence of spin-Peierls instability. It is explicitly shown that the string long range order survives even in the presence of randomness. The string order behaves as u
2β with β -- 0.37 in agreement with the recent prediction of real space renormalization group theory (β =(3-√5)/2 ~= 0.382). The physical picture of this behavior in this model is also discussed.
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