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Kazumitsu Sakai
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 6 Pages
1789-1792
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The excited state thermodynamic Bethe ansatz (TBA) equations for the spinless Fermion model are presented by the quantum transfer matrix (QTM) approach. We introduce a more general family called T-functions and explore functional relations among them (T-system) and their certain combinations (Y-system). From their analytical property, we derive a closed set of non linear integral equations which characterize the correlation length of ‹ c
j†c
i› at any finite temperatures. Solving these equations numerically, we explicitly determine the correlation length, which accurately coincides with previous results.
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Jun–ichi Sakai, Yoshihiro Kazimura, Takayuki Haruki
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 6 Pages
1793-1796
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We investigate the dynamics of the collision of narrow plasma clouds, whose transverse dimension is on the order of the electron skin depth. A 2D3V (two dimensions in space and three dimensions in velocity space) particle-in-cell (PIC) collisionless relativistic code is used to show the generation of a quasi-static magnetic field during the collision of narrow plasma clouds both in electron-ion and electron-positron (pair) plasmas. The localized strong magnetic fluxes result in the generation of the charge separation with complicated structures, which may be sources of electromagnetic as well as Langmuir waves. We also present one application of this process, which occurs during coalescence of magnetic islands in a current sheet of pair plasmas.
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Mamoru Yamashita, Satoshi Tanaka
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1797-1800
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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To clarify the mechanism of successive phase transitions occurring in ferroelectric and antiferroelectric smectic liquid crystals, a crossover behaviour of the XY model with competing second nearest neighbour interaction exposed to a twofold field to the Ising model (axial next nearest neighbour Ising model) is studied at finite temperature. The phase transition line from an ordered phase with Ising symmetry to the one preserving characteristics of the XY model is shown to lie at the low-temperature side of a critical curve between the former and a disordered phase, which leads to the result that the freedom of the XY spin is suppressed more strongly at finite temperature than at the absolute zero temperature. A phase with a structure of period 6 is analysed in detail as a typical case of modulated phases with the freedom of XY spin.
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Masahiro Nakano
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1801-1804
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Spectacularly angle-dependent quantum-oscillations whose frequencies are the combinations of the fundamental frequencies of the individual bands are predicted to be observed in quasi two-dimensional (Q2D) multiband electronic Fermi liquids, such as Sr
2RuO
4, owing to the chemical potential oscillation (CPO) and Yamaji effect. Both the high two-dimensionality and weak three-dimensionality of the Q2D system are essential for the angle-dependent phenomena. The temperature dependence of the combination frequency components due to the CPO is found to be differ from that due to the magnetic interaction.
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Hiroaki Kusunose, Yoshio Kuramoto
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1805-1808
Published: June 01, 1999
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We show that a Kondo-type model with an orbital degeneracy has a new non-Fermi-liquid fixed point. Near the fixed point the spin degrees of freedom are completely quenched, and the residual charge degrees of freedom lead to the multichannel Kondo effect. Anomalous behavior appears in electric and thermal properties, but the magnetic susceptibility should show the local Fermi-liquid behavior. The non-Fermi-liquid fixed point becomes unstable against perturbations breaking the particle-hole symmetry. We derive these results using the third-order scaling for a spherically symmetric model with a fictitious spin. In contrast to the Coqblin-Schrieffer model, the present model respects different time-reversal properties of multipole operators.
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Masahisa Tsuchiizu, Hideo Yoshioka, Yoshikazu Suzumura
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1809-1812
Published: June 01, 1999
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The charge gap in a quarter-filled organic conductor, which is induced by dimerization and/or alternating potential is studied by applying the renormalization group method to the bosonized one-dimensional Hamiltonian. The interplay of dimerization and alternating potential gives rise to the unconventional enhancement of the charge gap in addition to the on-site repulsive interaction. The experimental results of resistivity and optical conductivity in Bechgaard salts are examined based on the present calculation.
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Tetsuji Kuramoto
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
1813-1816
Published: June 01, 1999
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We study the S=1/2 and S=1 alternating spin Heisenberg chain with the next-nearest neighbor (NNN) interaction J
2 between neighboring S=1/2 spins, by using the numerical diagonalization method of a finite size system. It is found that a fractional plateau appears at magnetization m=1/2 in the magnetization curve for J
2>J
2c=0.106± 0.001. The phase transition at J
2c is characterized by the exponent σ=1, which controls the critical behavior of the spin gap Δ as Δ-- exp(-a/(J
2-J
2c)
1+σ). For J
22c, the model at m=1/2 is described by the conformal field theory with central charge c=1 and exponent η for the spin correlation function of the transverse component to a magnetic field is calculated.
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Keita Kishigi, Yasumasa Hasegawa, Mitake Miyazaki
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
1817-1820
Published: June 01, 1999
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The effects of the Zeeman term on the de Haas-van Alphen oscillation are studied in the magnetic breakdown system. We find that the amplitudes of the oscillations with the frequencies of f
β+f
α and f
β+2f
α are enhanced by the Zeeman term, while they are expected to be reduced according to semiclassical theory. A possible interpretation of the experiments in organic conductors is discussed.
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Hiroshi Kageyama, Kenzo Onizuka, Touru Yamauchi, Yutaka Ueda, Shingo H ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
1821-1823
Published: June 01, 1999
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The magnetic properties of a two-dimensional spin-gap compound SrCu
2(BO
3)
2, realizing the Shastry-Sutherland model, were investigated using high-quality single crystals. The analysis of the temperature-dependent magnetic susceptibility revealed a spin gap of 34, K. The magnetization curve at 0.4, K possibly has, in addition to the already established one-quarter and one-eighth plateaux, another quantized plateau at one-tenth of the full Cu moment, which is one of the plateaux predicted by Miyahara and Ueda.
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Hiroji Ohigashi, Kenji Omote, Hideto Abe, Keiko Koga
Subject area: Dielectric properties and materials.
1999 Volume 68 Issue 6 Pages
1824-1827
Published: June 01, 1999
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An anomalously large dielectric constant and a long relaxation time along the chain axis were first observed in the paraelectric phase of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. Dielectric, X-ray scattering and shear sound velocity studies consistently show that the anomalous phenomena arise from the characteristic motion of a chain molecule of TGTG
′ chain conformation in the crystal: the chain in the paraelectric phase rotates independently of neighboring chains, and, in the chain, a TGTG
′ sequence, whose length increases around the Curie temperature, undergoes the flip-flop motion. The crystal in the paraelectric phase is a liquid crystal of 1D liquid and 2D solid.
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Koshi Takenaka, Kenji Iida, Yuko Sawaki, Shunji Sugai, Yutaka Moritomo ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1999 Volume 68 Issue 6 Pages
1828-1831
Published: June 01, 1999
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Optical reflectivity spectra were measured on cleaved surfaces of La
1-xSr
xMnO
3 single crystals (0≤ x ≤ 0.30). The optical conductivity σ(ω) shows, keeping single-component nature, an incoherent-to-coherent crossover with a spin polarization of conducting e
g electrons. The σ(ω) spectrum of the ferromagnetic-metal La
0.70Sr
0.30MnO
3 is characterized by a pronounced Drude-like component with large spectral weight below --1.6 eV, which yields a large effective carrier number N
*eff consistent with the results of other techniques. The present result demonstrates that the previous result of “small Drude weight” is due to a deterioration of the sample surface, at least for the heavily doped region.
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Hilmi Demiray
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 6 Pages
1833-1837
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The basic equations describing the nonlinear ion-acoustic waves in a cold collisionless plasma, in the longwave limit, is re-examined through the use of a modified reductive perturbation method. Introducing the concept of a scale parameter and expanding the variables and the scale parameter into a power series of the smallness parameter ε , a set of evolution equations is obtained for various order terms in the perturbation expansion. To illustrate the present derivation, a localized travelling wave solution is studied for the derived field equations and the result is compared with those of obtained by Sugimoto and Kakutani rf:3 who introduced some slow scales, Kodama and Taniuti rf:4 who employed the renormalization method and Malfliet and Wieers, rf:6 who employed the dressed solitary wave approach from the outset of their study.
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Hiroaki Ono, Isamu Nakata
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 6 Pages
1838-1842
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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By the reductive perturbation method, effects of internal loss on electromagnetic waves propagating in the nonlinear dielectric medium parallel to an external magnetic field are investigated. The resultant equation takes the form of derivative nonlinear Schrödinger equation with an additive dissipation term, which is shown to admit the exact shock wave solution combining an empty state and a uniform state with non-vanishing boundary value. In weaker nonlinear cases, we can explicitly show that there exist more general shapes of shock wave solutions, which combine two different uniform states. In both cases, a rarefaction type of shock wave is possible in the medium with nonlinearly softer anharmonic force. These results suggest the general existence of another fundamental nonlinear wave different from solitons in general systems subject to a derivative nonlinear Schrödinger equation in the absence of dissipation.
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Rei Inoue, Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 6 Pages
1843-1846
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We construct the quantum integrable dynamical system on a (2+1)-dimensional lattice.We consider the q-commuting operators on 2-D lattice as adiscretization of the current algebra, and two evolution operators are explicitly defined interms of the quantum dilogarithm function.
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Derek W. C. Lai, Kwok W. Chow
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 6 Pages
1847-1853
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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`Positon' and `dromion' solutions are derived for the long wave-short wave interaction equations in a two-layer fluid. Positons are new, exact solutions of nonlinear evolution equations that exhibit algebraic decay in the far field. A positon solution can be generated by taking a special limit of multi-soliton expansion. Variation of the limiting process yields different solutions. Dromions are exact, localized solutions of (2+1) dimensional (2 spatial, 1 temporal) nonlinear evolution equations that decay exponentially in all directions. One and higher dromion solutions are investigated, and a particular case of higher dromion solutions is considered in details. By applying another limiting procedure a new solution is generated. This method of `coalescence of eigenvalues' or `wavenumbers' is thus quite universal, and can be applied to a wide variety of expansions, not just the multi-soliton type. Finally, the case of propagation solutions on a continuous wave background is also studied.
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Hui–Hui Dai
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 6 Pages
1854-1858
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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This paper studies a variable-coefficient KdV (vcKdV) equation arising in a shallow water. For a practically acceptable water bottom, we find that it can be transformed into the cylindrical KdV equation. As a result, several exact bounded solutions are obtained. One of the solutions has the shape of a solitary wave with a shelf behind, which confirms approximate analytical and numerical results in the literature.
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Masaru Sugiyama, Noriaki Sasaki
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 6 Pages
1859-1863
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The coefficient of restitution and the collision contact period are analyzed from a statistical-mechanical point of view through studying the collision between a one-dimensional anharmonic lattice and a rigid wall as a typical example. The contact period is defined as the time span between the first time and the last time when the atom at the end of the lattice contacts with the rigid wall. A similar collision problem for the harmonic lattice is also studied for the sake of comparison.
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Alexander N. Drozdov, Shigeo Hayashi
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 6 Pages
1864-1870
Published: June 01, 1999
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The mean relaxation time formalism employed previously in thesolution of one-dimensional Fokker-Planck equations is extended to ageneral diffusion process in arbitrary dimensions. The utility of the approach is demonstrated by calculating analytically the rate of noise-induced transitions in a bistable system without manifest detailed balance. The rate formula obtained summarizes in a uniform manner much of what had been done before in this field. Limitations of its validity arediscussed and a perturbation procedure to systematically improve it isproposed. The validity of our theoretical predictions for the rate isconfirmed by comparing with exact numerical results.
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Hirofumi Morise, Takeya Tsurumi, Miki Wadati
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 6 Pages
1871-1876
Published: June 01, 1999
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The stability of a two-component Bose-Einstein condensate is studied. Using the variational method, we investigate the stable and unstable conditions as functions of the particle numbers and the s-wave scattering lengths. We find that interaction between the different species of atoms (simply, interspecies interaction) has significant effects on the stability of each condensate.
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Takeshi Kuwamoto, Ichita Endo, Atsushi Fukumi, Takayoshi Horiguchi, Ma ...
Subject area: Atomic spectra and interactions of atoms with photons.
1999 Volume 68 Issue 6 Pages
1877-1882
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Hyperfine structures, isotope shifts and Stark effects of seven near-infrared transitions in Sm I are investigated by means of atomic-beam laser spectroscopy with fluorescence detection. E1 transitions from the ground-term
7F
1 --6 states of the 4f
66s
2 configuration to
9G
0 --6 states of the 4f
66s6p configuration are measured. The
9G
1, 2, 3 states are promising candidates for measuring the parity nonconserving effects in Sm. Hyperfine constants A and B for odd-mass isotopes of
147Sm and
149Sm are newly determined for the six upper states studied. Isotope shifts of the transitions are determined, and specific mass shift and field shift are also obtained by King-plot analysis. Stark splittings are resolved for three transitions and tensor polarizabilities of the upper states are determined.
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Abraham Medina, Casay Treviño
Subject area: Mechanics, elasticity, and rheology.
1999 Volume 68 Issue 6 Pages
1883-1886
Published: June 01, 1999
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In this work we have studied the hysteretic behavior for the mean slope of the free surface of noncohesive granular media under axisymmetrical rotation. In order to study the hysteresis loop the relationship between the average slope of the free surface (most important measurable quantity) and the Froude number has been established. Differences between experiments and theoretical predictions are also shown. Theory predicts that hysteresis must disappear as the friction coefficient μ of the granular material reaches unity. However, this condition could not be reached experimentally using tapioca (where μ -- 1), due to the important difference between the angle of internal friction and the angle of repose for small containers.
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Emin Fuad Kent
Subject area: Fluid dynamics.
1999 Volume 68 Issue 6 Pages
1887-1890
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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This paper presents visualization photographs of cellular Stokes flow induced by rotation of a circular cylinder in a V-shaped channel bounded by a cylindrical surface. The source of motion that is the inner rotating cylinder is positioned at the center of the cylindrical surface, as well asat different locations inside this channel. Many interesting flow patternshave been visualized using solid tracers of magnesium illuminated by a thin sheet of light coming from a laser device. Some quantitative data have been deduced from these visualization photographs. The influence of the outer boundary onthe flow structure is analyzed and a comparison is made.
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Sanae–I. Itoh, Kimitaka Itoh
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 6 Pages
1891-1906
Published: June 01, 1999
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A statistical description is developed for a self-sustained subcritical turbulence in inhomogeneous plasmas. Interchange mode in the presence of inhomogeneous magnetic field, which reveals a submarginal strong turbulence, is considered. Nonlinear dispersion relation is extended to a Langevin equation for a dressed test mode, in which nonlinear interactions are kept as renormalized drag and random self noise. Based upon the assumption that the random noise has a faster time scale, the solutions are obtained for the fluctuation level, decorrelation rate, auto- and cross-correlation functions and spectrum. They are expressed as nonlinear functions of non-equilibrium parameters like gradient. Extended fluctuation-dissipation theorem (Einstein relation) is described as statistical relations. Then the Langevin equation is reformulated into a Fokker-Planck equation of the probability distribution function. The steady state probability function is solved. Imposing the constraint of the self-noise, the power-law distribution with respect to the fluctuation amplitude is obtained in the tail of the distribution function.
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Kozo Hoshino, Fuyuki Shimojo, Taiji Nishida
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 6 Pages
1907-1911
Published: June 01, 1999
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The structural change in a Se chain and a Se
8 ring due to the excitation of an electron in the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) is investigated by an ab initio molecular-dynamics simulation to clarify the possibility of bond breaking. It is shown, from the calculated time dependence of the bond lengths, the energy eigenvalues and the wavefunctions, that there occurs a photo-induced bond breaking in both cases and that such a bond breaking is closely related to the stabilization of the anti-bonding LUMO state. This photo-induced bond breaking may be considered as an elemental process for the recently observed photo-induced semiconductor-metal transition in liquid Se near the triple point. The results for Se
8 ring are also compared with our previous results for S
8 ring.
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Fujio Kakinuma, Toshiharu Fukunaga, Kenji Suzuki
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 6 Pages
1912-1916
Published: June 01, 1999
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The structure of liquid S
100-xTe
x mixtures with x=30, 50, 61 and 80 has been investigated. The total pair correlation functions exhibit three distinct peaks, which can be assigned to the correlation of S--S, S--Te and Te--Te. The results indicate that liquid S--Te mixtures retain a chain structure. The g(r) shows systematic variation due to the composition dependence of the weighting factors for three partial g
ij(r) except the one for liquid S
39Te
61. The change in the g(r) for liquid S
20Te
80 at around 3.10, Å caused by the inter-chain interaction may be responsible to the nonmetal-metal transition. Substantial differences in the g(r) for liquid S
39Te
61 may be closely related to the existence of the two-phase region with a closed loop.
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Yosuke Yoshimura
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 6 Pages
1917-1931
Published: June 01, 1999
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Molecular association of the solute molecules in a one-dimensional square-well fluid is studied under the infinitely dilute condition over a wide density region. A statistical mechanical formalism of the one-dimensional fluid is given. Different aspects of the molecular association are extracted by several measures such as the distribution function at the contact distance. The effect of the solute-solvent interaction is discussed in view of the number of the “bond” that is assumed for a pair of solute and solvent molecules in the potential well. The bond-number distribution in the region confined by a pair of solute molecules is responsible for the complicated change of the solute-solute distribution function by the solute-solvent interaction at the distant region. It is shown that the change of the bond number with the solute-solute distance is expressed by the solute-solute distribution functions with the shifts in distance by the width of the potential well at zero solute-solvent interaction.
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Masatoshi Saito, Shinchul Kang, Kazumasa Sugiyama, Yoshio Waseda
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 6 Pages
1932-1938
Published: June 01, 1999
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The three partial structural functions of molten AgBr have been determined by using a combination of the anomalous X-ray scattering (AXS) data and conventional neutron diffraction result. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique. The partial structure factor of a
AgAg(Q) in molten AgBr was rather broad than that found in molten alkali halides such as RbBr. The resultant structural parameters suggest that the structure of molten AgBr is quite likely described by disordered close packing of Br ions where Ag ions are distributed in both octahedral and tetrahedral holes.
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Aloka Sinha, Tetali A. Prasada Rao, Roman Dabrowski
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1939-1942
Published: June 01, 1999
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Measurements are reported for the first time on the D.C. Kerr response and the pre-transitional behaviour of two liquid crystalline isothiocyanates 4-(4
′-n-pentyl phenyl)-phenyl isothiocyanate (5NCS) and 4-(4
′-n-heptyl phenyl)-phenyl isothiocyanate (7NCS) at temperatures above the smectic-isotropic transition temperatures. The Kerr law has been verified and the real part of the third order nonlinear susceptibilities (χ
(3)) above the smectic-isotropic transition are determined for the two liquid crystalline isothiocyanates from the electro-optic Kerr effect (EOKE) experiments. The variation of susceptibility with temperature has also been studied. The results have been compared with the cyanobiphenyls which have been widely studied and are known for their giant optical non-linearities.
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Susumu Shimomura, Keisuke Tajima, Nobuyoshi Wakabayashi, Shiho Kobayas ...
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1943-1947
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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X-ray diffraction measurements have been performed on Nd
0.5Sr
0.5MnO
3 single crystals at various temperatures and magnetic fields. The temperature dependences of the lattice parameters show abrupt changes in the slopes at the ferromagnetic transition temperature of 250 K. Discontinuous changes in the lattice parameters occur at the charge-ordering transition temperature of 165 K, below which Mn
3+ and Mn
4+ ions are spatially ordered. In the ferromagnetic phase, the orthorhombic lattice distortion is reduced with decreasing temperature. This behavior can be attributed to a magnetoelastic interaction in this compound. Superlattice reflections corresponding to a doubling of the unit cell along the b axis appear in the charge-ordered phase, and their intensities change very little with temperature and magnetic field except near the transition. When the charge-ordered phase is transformed into the ferromagnetic phase by an external magnetic field, the superlattice reflections vanish and the lattice parameters discontinuously change. Values of the magnetic fields at which the transition occurs are independent of directions of applied magnetic fields.
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Miroslaw Maczka, Seiji Kojima, Jerzy Hanuza
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1948-1953
Published: June 01, 1999
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Phase transitions in KSc(WO
4)
2 have been studied by means of Raman spectroscopy. Two soft modes and the splitting of doubly degenerate modes into doublets have been observed below 307, K. The observed broadening of lattice modes and anomalous behavior of the librational mode around 60, cm
-1 have been explained as a result of rotational disorder of the WO
42- ions. This may support the conclusion derived from the ESR studies that the crystal is incommensurate below 307, K.
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Ioan Bâldea, Horst Köppel, Lorenz S. Cederbaum
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1954-1962
Published: June 01, 1999
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We describe quantitatively the structural change in finite Peierls chains. Full quantum mechanical calculations show: (i) how the smooth phase transition occurs by the continuous change of the ground state wave function which preserves the symmetry of the Hamiltonian; (ii) the structural change is accompanied by an anharmonicity which becomes very pronounced in the broad transition region; (iii) the dimerization is suppressed for sizes shorter than a certain critical size. Quantum phonon fluctuations can make the latter sufficiently large ({--} 0.1 - 1 μm) to be detected in mesoscopic systems (e.g. perylene radical cation salts) with weaker electron-phonon coupling. As possible techniques for experimental observation, we suggest the nonlinear optical absorption and the ultrasonic attenuation. Our calculations are based on numerical diagonalization done exactly in small chains and within the adiabatic ansatz for longer chains. We indicate how to test selfconsistently the latter results and show that they are accurate up to mesoscopic sizes in parameter ranges of relevance for real systems. We explain why conventional many-body techniques are inappropriate to describe the Peierls transition in finite chains.
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Koh–ichi Suzuki, Shin"ichi Ishimaru, Ryuichi Ikeda
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 6 Pages
1963-1967
Published: June 01, 1999
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The
133Cs NMR spin-lattice relaxation times (T
1) in Cs
2MBr
4 (M=Cd and Hg) crystals were measured in a range of 207--369, K and 197--369, K, respectively. Critical exponents ζ at the normal-incommensurate phase transition were determined to be ζ =0.62± 0.02 and 0.50± 0.02 for M=Cd and Hg, respectively, in good agreement with the three-dimensional XY and the mean field models in the same order. Frequency dependent T
1 values observed in the incommensurate phase of both compounds could be explained by fluctuations of amplitudons and phasons with a small gap.
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Hiroki Akutsu, Kazuya Saito, Yasuhisa Yamamura, Koichi Kikuchi, Hiroyu ...
Subject area: Thermal properties of condensed matter.
1999 Volume 68 Issue 6 Pages
1968-1974
Published: June 01, 1999
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Temperature dependence of the heat capacities of two organic conductors, (DMET)
2BF
4 and (DMET)
2ClO
4, was measured by chopped-light ac calorimetry between 10 and 300, K. A “Mott-like” nature of the metal--insulator transition around 32, K was confirmed by the absence of thermal anomaly. A magnetic transition showed an anomaly around 18, K for the ClO
4- salt and at 19, K for the BF
4- salt. The smallness of the anomaly due to the transition is consistent with the suggested SDW formation. A frequency-dependent step in heat capacity was detected around 110, K. The step-like anomaly is attributed to a glass transition due to the freezing of the intramolecular motion of the ethylene group in the BEDT-TTF moiety within a DMET molecule.
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Hiroshi Yamagami
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1975-1981
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Ab-initio calculations of the electronic structure for non-magnetic heavy-fermion cerium compound CeNi
2Ge
2 and the reference material LaNi
2Ge
2 have been performed by an all-electron fully-relativistic augmented-plane-wave (RLAPW) method with an exchange-correlation potential in a local-density approximation. The Fermi surfaces for the two compounds are calculated to investigate a dependence of 4f electrons in the bands near the Fermi energy. The obtained Fermi surface of LaNi
2Ge
2 can account well for origins of the branches observed by the de Haas-van Alphen (dHvA) effect. The calculated cyclotron mass for the dHvA branches is quantitatively comparable with the observed one, corresponding to a small enhancement factor estimated from the electronic specific heat coefficient. In order to elucidate theoretically-predicted dHvA branches for CeNi
2Ge
2, the dHvA frequencies along the symmetry axes are calculated together with the cyclotron mass.
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Shugo Suzuki, Kenji Nakao
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1982-1987
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We present a fully relativistic full-potentiallinear-combination-of-atomic-orbitals method for solids based on thedensity-functional theory within the local-density approximation. Wesolve the Dirac-Kohn-Sham equations directly, handling not only theindirect relativistic effect but also the effect due to the spin-orbitcoupling self-consistently. We apply the present method to Au andInSb and compare the results with those of experimental and othertheoretical studies. Consequently, we show that the agreement is goodand the present method is capable of obtaining reliable results instudying the structural and electronic properties of solids.
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Hiroyuki Shiba, Osamu Sakai, Ryousuke Shiina
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1988-1993
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The interaction between nearest-neighbor Ce ions mediated by conduction electrons is carefully analyzed for CeB
6 by fully taking into account the symmetry connecting two Ce ions as well as the nature of Γ
8 wave functions. It is shown that the interaction Hamiltonian resulting from the analysis has a simple form containing a very few parameters because of constraints due to the symmetry. It is concluded quite generally from the interaction Hamiltonian that when the AF quadrupole-quadrupole interaction of Γ
5-type is strong, the AF octupole-octupole interaction of T
xyz type is equally strong. Thus the present analysis gives a strong support to the importance of T
xyz octupoles in CeB
6.
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Hideo Fujita, Kenji Yamauchi, Akihiko Akasaka, Hiroshi Irie, Shoji Mas ...
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 6 Pages
1994-1996
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The absorption spectra of the alkali and the cuprous halides under hydrostatic pressure were measured at room temperature. The first exciton peak shows a linear blue shift with increasing pressure. Ionic index I for ionic crystals and cubic semiconductors is defined and estimated. It is found that the ionic index I is almost 1 for the alkali halide. As the ratio of the covalent bond to the ionic bond increases, the ionic index I becomes smaller than 1.
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Osamu Takagi, Tetsuro Saso
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 6 Pages
1997-2005
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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A new scheme is proposed for calculating excitation spectrum of a quantum dot expressed by the impurity Anderson model. It is based on the second order perturbation theory with respect to the Coulomb repulsion, but is modified so as to reproduce the correct atomic limit and to fulfil the Friedel sum rule.The magnetic field dependence of both the excitation spectra and the transport properties of a quantum dot is investigated. It is found that the zero bias peak in differential conductance splits under external magnetic field and that negative magnetoresistance will be observed at zero bias voltage in case of electron-hole asymmetry.
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Koji Kobayashi, Shinichiro Suzuki, Hisashi Oshima, Ko Sugihara
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 6 Pages
2006-2009
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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c-axis thermoelectric power (TEP) of stage-2 IBr-GIC exhibits a linear temperature dependence at low temperature, which ascribed to the diffusion term. Around 80, K its slop becomes gently. This implies that the in-plane phonon scattering plays an important role in the conduction process. By choosing an appropriate parameter set the diffusion term can be calculated. However, in the range 40--170, K the diffusion term cannot provide a good fit with the observed TEP. By introducing the phonon drag term, therefore, we obtain a good agreement with the observed data.
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Tomio Koyama
Subject area: Superconductivity.
1999 Volume 68 Issue 6 Pages
2010-2018
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We present a new microscopic theory based on the quantum electrodynamics for the longitudinal Josephson plasma in strongly anisotropic high-T
c superconductors. The longitudinal electric field is quantized in terms of the phason gauge in which the phason velocity is self-consistently determined. The longitudinal photon propagator is calculated within the 2nd order tunneling process from which the Josephson effect arises. The longitudinal dielectric function is also derived. The dispersion relation and the temperature dependence of the longitudinal Josephson plasma propagating in the direction of the layer stacking is calculated from the dielectric function. It is predicted that the Josephson plasma frequency vanishes at T
c in the case where the interlayer coupling constant is less than some critical value.
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Masashi Yamashiro, Yukio Tanaka, Nobukatsu Yoshida, Satoshi Kashiwaya
Subject area: Superconductivity.
1999 Volume 68 Issue 6 Pages
2019-2025
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Tunneling conductance spectra in normal metal / insulator / triplet superconductorjunctions are theoretically investigated.For the triplet paring states, we select several kinds of the symmetrieswhich are promising candidates for the superconducting statesof UPt
3 and Sr
2RuO
4.We present a conductance formula that can treatspatially varying pair potential witharbitrary barrier height cases.In order to analyze realistic situations, thepair potentials are determined self-consistentlyusing the quasi-classical Green's function method.It is shown that the pair potentials exhibit diverse spatial dependencesnear the insulator.The conductance spectra show zero-bias conductance peaksas well as gap structures depending on the junction orientation, which qualitatively agrees withour previous calculation where the pair potentialsare assumed to be spatially constant.The agreement implies an insensitive natureof the tunneling conductance spectra onthe detailed spatial profile of the pair potential.
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Toshifumi Taniguchi, Yoshikazu Tabata, Yoshihito Miyako
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2026-2032
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We have studied the magnetic properties of the mixed compound Ce(Ru
1-xRh
x)
2Si
2 (0.3 ≤ x ≤ 0.5) by means of specific heat and magnetization measurements with single crystalline samples. The C/T, specific heat divided by T, shows a logarithmic temperature dependence between 0.1 and 10 K for x=0.4 and 0.5 and the susceptibility conforms to 1 - T
1/2 and 1 - T
1/3 in the temperature range of 1.8 K and 10 K, respectively. These non-Fermi liquid behaviors are studied on the basis of self-consistent renormalization theory and Kondo disorder model. However, their magnetic properties seem not to be explained simply by such theories, especially as inferred from very large non-linear susceptibility.
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Takao Mori, Takaho Tanaka
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2033-2039
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Static magnetic susceptibility of the new B
12 icosahedral higher boride compound TbB
50 was measured and a large change in behavior around 17 K was observed, indicating the existence of an antiferromagnetic-like transition.At high fields a metamagnetic transition was observed to occur and the magnetic phase diagram was determined.This is the first report of a magnetic transition being observed in the higher boride compounds. An interesting feature of this behavior is that it is in contrast to the typical Curie-Weiss behavior of the more terbium rich compound TbB
25 and also the more boron rich compound TbB
66 which were also synthesized and measured in this work. This is considered to be an aspect of the unique structure of the REB
50 (RE=rare-earth) compounds recently discovered.
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Masaya Kato, Shunsuke Yoshii, Masatoshi Sato
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2040-2045
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Effects of Cu-site substitution with Zn, Co and Ni on the spin-gapped state of CuNb
2O
6, which has ferromagnetic-antiferromagnetic alternating spin (S=1/2) chains of Cu
2+ ions, have been studied by measuring the magnetic susceptibilities and the specific heats. The results indicate that impurity atoms induce an “isolated” magnetic moment mainly at one of the neighboring Cu sites originally connected with the antiferromagnetic exchange interaction, with the other part of Cu sites being essentially kept in the spin-gapped states. For Co
2+ (Ni
2+) impurities, localized spins with S=2 (3/2) are formed by the ferromagnetic coupling between the impurity spins and the induced ones (note that the coupling is now ferromagnetic even though it is antiferromagnetic in the undoped system).
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Haruhiko Kuroe, Jun–ichi Sasaki, Tomoyuki Sekine, Takatsugu Masu ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2046-2056
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We have studied Zn- and Si-doping effects on the 368-cm
-1 folded phonon in the spin-Peierls (SP) systems Cu
1-xZn
xGeO
3 and CuGe
1-ySi
yO
3 by means of Raman scattering.The folded phonon is induced by the formation of the superlattice.The Raman intensity at 6 K decreases almost linearly with increasing dopant concentration.The temperature dependence of Raman intensity and the broad line shape in the x = 0.021 Zn-doped crystal indicate that the SP long-range order is not formed in this sample.In the low-temperature antiferromagnetic (AF) phases in lightly doped crystals, we observe the sharp folded phonon mode, indicating that the lattice dimerization persists in this phase.No sharp Raman line from the folded phonon is observed in the AF phase of the x=0.021 Zn- and y=0.04 Si-doped crystals, indicating the existence of the uniform AF phase in these samples.
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Hiroki Yamauchi, Hideya Onodera, Kenji Ohoyama, Takahiro Onimaru, Masa ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2057-2066
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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Magnetic properties were investigated on a single-crystalline DyB
2C
2 compound with the tetragonal structure. Spontaneous magnetizations appear along the a- and [1 1 0]-directions below T
C=15.3 K. A very small shoulder is observed only along the c-axis at T
Q=24.7 K, although large λ-type anomalous specific heats are observed at T
C and T
Q. There exists a large magnetic anisotropy in the tetragonal basal plane which is observed in magnetization processes below T
C. Neutron powder diffraction experiments reveal that magnetic reflections are observed only below T
C. In the magnetically ordered phase, the Dy moments are arranged to be perpendicular to neighbors along the c-axis. The results are well interpreted by postulating that the phase between T
C and T
Q is an antiferroquadrupolar ordered one. DyB
2C
2 is a novel compound with a high antiferroquadrupolar ordering temperature of 24.7 K.
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Tatsuhiro Nozue, Hisao Kobayashi, Takashi Kamimura, Takuya Kawakami, H ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2067-2072
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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We have measured the de Haas--van Alphen effect at 0.55 K in the field up to 9.5 T for the single crystal of Pauli paramagnetic NiAs. Six dHvA branches have been observed and they show complicated behavior as a function of the field direction which is applied in the symmetry planes (1120), (1010) and (0001). The corresponding cyclotron masses have been also determined from the temperature dependence of the dHvA amplitude. To discuss the experimental results we have performed the electronic band calculation of NiAs for the non-magnetic state by using the full potential LAPW method. The total energy calculated as a function of the lattice parameter a, keeping the ratio c/a as the observed value, becomes minimum at 3.60 Å, which agrees very well with the observed one. The Fermi surface is found to consist of two kinds of hole surface around the ΓA axis and one electron surface with six fold symmetry. For each Fermi surface we have calculated dHvA oscillation frequencies and succeeded to explain the field dependence of some of the observed frequencies. The calculated cyclotron masses are compared with the observed ones.
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Shinji Watanabe, Hisatoshi Yokoyama
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2073-2097
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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The bulk properties and impurity effect in the one-dimensional S=1/2 Heisenberg model with dimerization and next-nearest-neighbor exchange are studied by the density matrix renormalization group and exact diagonalization methods. This model widely covers the S=1 Heisenberg model, two-leg ladders, bond-alternating chains and the S=1/2 Heisenberg model. Almost the whole parameter space belongs to the Haldane phase. In the non-dimerizing limit a transition to a kind of spin liquid takes place, characterized by the delocalized spin polarization. This transition causes the distinct impurity effects between a spin-Peierls compound CuGeO
3 and the Haldane systems. Experimental aspects of a bond-alternating compound CuNb
2O
6 are also discussed. Furthermore, the incommensurate correlation arising in this model is extensively studied, and a phase diagram is constructed.
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Norihiro Muramoto, Minoru Takahashi
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2098-2104
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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An exact solution for an XXZ chain with four-body interactions is obtained and its phase diagram is determined. The model can be reduced to two chains coupled by four-body interactions, and it is shown that the ground state of the two-chain model is magnetized in part. Furthermore, a twisted four-body correlation function of the anti-ferromagnetic Heisenberg chain is obtained.
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Ryousuke Shiina, Hiroyuki Shiba, Osamu Sakai
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 6 Pages
2105-2117
Published: June 01, 1999
Released on J-STAGE: October 01, 1999
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A theory of the antiferro-quadrupolar (AFQ) ordering in TmTe is presented on the basis of a classical description of multipoles. The phase diagram of the AFQ state and its relation to the type of crystal field and the form of multipolar interactions are studied in detail.It is shown that the Γ
3-AFQ order parameter in a crystal field with the (001)-easy-axis type is uniquely consistent with the magnetic-field anisotropy observed in TmTe. A correlation is present between the spontaneous and field-induced antiferromagnetic orders through the magnetic interaction in the AFQ state; it leads to a natural interpretation of the phase diagram of TmTe. A large contribution from octupoles on the AFQ transition temperature is predicted in the high-field region due to the cooperative relation of octupoles and the magnetic field.
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