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Ayse Karasu-Kalkanli, Atalay Karasu, Sergei Yu. Sakovich
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1165-1166
Published: 2001
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It is shown that a generalized Ito system of four coupled nonlinear evolution equations passes the Painlevé test for integrability in five distinct cases, two of which were introduced recently by Tam
et al. [H. W. Tam, X. B. Hu, D. L. Wang: J. Phys. Soc. Jpn.
68 (1999) 369]. A conjecture is formulated on integrability of a vector generalization of the Ito system.
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Yoko Suzuki, Yoshitaka Tanimura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1167-1170
Published: 2001
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Quantum coherence and its destruction by coupling to a dissipative environment play important roles in time-resolved optical response. We study a two-time correlation function of a two-dimensional rotator coupled to a harmonic-oscillator bath. Generating functionals of reduced density matrix elements for the rotator degrees of freedom are calculated by diagonalizing the total Hamiltonian with the use of unitary transformations and then performing path integrals. A closed-form expression of linear absorption spectrum for a dipole rotator, i.e., a Fourier transformation of the dipole two-time correlation function, is derived from the generating functionals characterized by the bath spectral density. Based on the theory, the spectra for a methyl rotation in a toluene are depicted for various damping constants and temperatures. Because of the cyclic boundary condition that is constrained to fit the rotator degree of freedom, the energy states of the rotator in the absence of damping are discrete: the spectra consist of rotational branches, which correspond to change of the angular momentum. Owing to damping, the spectra exhibit a continuous band which is broadened as temperatures increase.
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Jiro Mizushima, Takashi Inui
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1171-1174
Published: 2001
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Transitions of three-dimensional flow through a symmetric rectangular duct with a suddenly expanded and contracted part are investigated by numerical simulations and bifurcation analyses of the numerical simulation data. The flow is steady and symmetric at low Reynolds numbers, makes a transition to a steady asymmetric flow at a critical Reynolds number owing to a symmetry-breaking pitchfork bifurcation and recovers the symmetry at another critical Reynolds number. Our attention is focussed on the side-wall effect upon the critical Reynolds number for the first pitchfork bifurcation. It is found that the critical Reynolds number is proportional to the inverse of the width of the duct. The three-dimensional flow structure is discussed in comparison with the two-dimensional one.
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Mitsuhiro Nambu, B. J. Saikia, T. Hada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1175-1177
Published: 2001
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The effect of the external magnetic field on the wake potential of a test dust particulate due to ion-sound waves in a dusty plasma with streaming ions is determined. The result shows that the amplitude of the wake potential is significantly reduced because the overshielding by streaming ions is inhibited by the presence of the external magnetic field.
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Hajime Tanaka
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1178-1181
Published: 2001
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We propose that the boson peak originates from the (quasi-) localized vibrational modes associated with long-lived locally favored structures, which are intrinsic to a liquid state and are randomly distributed in a sea of normal-liquid structures. This tells us that the number density of locally favored structures is an important physical factor determining the intensity of the boson peak. In our two-order-parameter model of the liquid-glass transition, the locally favored structures act as impurities disturbing crystallization and thus lead to vitrification. This naturally explains the dependence of the intensity of the boson peak on temperature, pressure, and fragility, and also the close correlation between the boson peak and the first sharp diffraction peak (or prepeak).
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Shunji Tuchiya, Susumu Kurihara
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1182-1185
Published: 2001
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We investigate the properties of skyrmion in the ferromagnetic state of spin-1 Bose-Einstein condensates by means of the mean-field theory and show that the size of a skyrmion is fixed to the order of the healing length. It is shown that the interaction between two skyrmions with oppositely rotating spin textures is attractive when their separation is large, following a unique power-law behavior with a power of -7/2.
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Shin-ichi Saito, Hiroyuki Yoshimoto, Yasuo Y. Suzuki, Susumu Kurihara
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1186-1189
Published: 2001
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We have performed a variational analysis on the evolution of superconductivity from weak to strong coupling regime. We have improved the Bardeen Cooper Schrieffer (BCS) wave function, and show that the electronic correlations are important in obtaining the correct behavior of superconducting condensation energy. In contrast to a crossover without thermodynamic anomaly discussed in a dilute system, we show the existence of a quantum phase transition near half filling, which suggests that an evolution is not always continuous. The transition is driven by charge density waves instabilities. We have found that superconductivity and charge density waves coexist in the presence of a weak intersite repulsion. The ground state phase diagram is determined by varying both interactions and filling.
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Katsuhiko Takegahara, Hisatomo Harima, Akira Yanase
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1190-1193
Published: 2001
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Crystal electric fields for the cubic point groups are reexamined and it is found that the new term O
62-O
66 is nonvanishing for the cubic point groups T
h and T due to the lack of Umklappung and fourfold symmetry axis of the point group O
h. The eigenfunctions and eigenvalues of the crystal electric field for 4f
n configurations are labeled by the irreducible representations of the point group T
h. The degeneracy of each sublevel does not change as compared with those of the point group O
h, but some eigenfunctions and eigenvalues are affected by the new term. Thus inelastic neutron scattering spectra for T and T
h are different from those for O
h due to different transition probabilities and selection rules.
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Yusuke Wakabayashi, Youichi Murakami, Yutaka Moritomo, Ichiro Koyama, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1194-1197
Published: 2001
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Hole concentration dependence of charge order (CO) and orbital order (OO) in layered perovskite compounds La
1-xSr
1+xMnO
4 has been studied by means of the resonant X-ray scattering technique. Both CO and OO are observed below 210 K in the compounds having the hole concentration x between 0.5 and 0.48, but neither is observed for x≤0.46. The transition temperatures are nearly independent of x between 0.5 and 0.48. Correlation lengths ξ's for both orders obtained from analyses of superlattice peak profiles are finite at any temperature. Moreover, in contrast to the cubic perovskite, ξ for OO is larger than that for CO. ξ for OO is as short as that for CO at the critical concentration of x=0.48. These results suggest that OO is prerequisite to the forming of CO in this system.
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Shoji Yamamoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1198-1201
Published: 2001
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Aiming to settle the controversial observations for halogen-bridged binuclear transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well as quantum, phase transitions are investigated with particular emphasis on the competition between electron itinerancy, electron-phonon interaction and electron-electron correlation. Recently observed distinct thermal behaviors of two typical MMX compounds Pt
2(CH
3CS
2)
4I and (NH
4)
4[Pt
2(P
2O
5H
2)
4I]·2H
2O are supported and further tuning of their electronic states is predicted.
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Kazuhito Itoh, Masaaki Nakamura, Norihiro Muramoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1202-1205
Published: 2001
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We show the existence of an exact ground state in a parameter regime of a one-dimensional half-filled extended Hubbard model with site-off-diagonal interactions. In this ground state, the bond-located spin correlation exhibits a long-range order. In the case when the spin space is SU(2) symmetric, this ground state degenerates with higher spin states including a fully ferromagnetic state. We also discuss the relation between the exact bond-ordered ground state and the critical bond-spin-density-wave phase.
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Shugo Suzuki, Shin'ichi Higai, Kenji Nakao
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1206-1209
Published: 2001
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We study two-dimensional σ-hole systems in boron layers by calculating the electronic structures of Mg
1-xNa
xB
2 and Mg
1-xAl
xB
2. In Mg
1-xNa
xB
2, it is found that the concentration of σ holes is approximately described by ( 0.8 + 0.8 x ) × 10
22 cm
-3 and the largest attainable concentration is about 1.6 × 10
22 cm
-3 in NaB
2. In Mg
1-xAl
xB
2, on the other hand, it is found that the concentration of σ holes is approximately described by ( 0.8 - 1.4 x ) × 10
22 cm
-3 and σ holes disappear at x of about 0.6. These relationships can be used for experimental studies on σ-hole systems in these materials.
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Shiro Kawabata
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1210-1213
Published: 2001
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A theoretical proposal for testing Bell's inequality in mesoscopic systems is presented. We show that the entanglement of two electron spins can be detected in the spin filter effect in the mesoscopic semiconductor / ferromagnetic semiconductor / semiconductor junction. In particular, we show how to test Bell's inequality via the measurement of the current-current correlation function in this setup. We also discuss the influence of an imperfect spin filter and derive the condition to examine the violation of Bell's inequality experimentally.
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Akito Kobayashi, Atsushi Tsuruta, Tamifusa Matsuura, Yoshihiro Kuroda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1214-1217
Published: 2001
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High-T
c superconducting materials (HTSC) have anomalous properties such as the pseudogap in the Hall coefficient, 1/T
1T and the density of states etc. First, including the effects of strong on-site repulsion between d-electrons at Cu-sites, we obtain quasi-particles with superexchange interaction J
s, whose band-width tends to reach zero, i.e., the system goes to the insulator, as δ tends to reach zero. The quasi-particles correspond to Zhang-Rice singlet states. J
s larger than the band width combined with the two-dimensional characteristic of the system induces strong antiferromagnetic fluctuations (AFF) and superconducting fluctuations (SCF). We treat effects of the AFF in the FLEX approximation and those of the SCF in the self-consistent t-matrix approximation to show that both fluctuations in the underdoped region start to increase at T
0 as T decreases from T» T
c, and that the AFF dominate the SCF at T>T
sg, while the SCF dominate at T<T
sg. This cross-over of the fluctuations causes the anomalous phenomena in the underdoped region. We also obtain the T-δ phase diagram of HTSC consistent with the one observed in experiments.
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Masatoshi Imada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1218-1221
Published: 2001
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Superconducting mechanism mediated by interband exchange Coulomb repulsion is examined in an extended two-band Hubbard models with a wide band crossing the Fermi level and coexisting with a narrower band located at moderately lower energy. We apply newly developed path-integral renormalization group method to reliably calculate pairing correlations. The correlation shows marked enhancement at moderate amplitudes of the exchange Coulomb repulsion taken smaller than the on-site repulsion for the narrower band. The pairing symmetry is s-wave while it has unconventional phases with the opposite sign between the order parameters on the two bands, in agreement with the mean-field prediction. Since the band structure of recently discovered superconductor MgB
2 shares basic similarities with our model, we propose that the present results provide a relevant clue for the understanding of the superconducting mechanism in MgB
2 as well as in this class of multi-band materials with good metallic conduction in the normal state.
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Seiji Niitaka, Hiroshi Kageyama, Kazuyoshi Yoshimura, Koji Kosuge, Shi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1222-1225
Published: 2001
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High-field magnetization and neutron diffraction measurements were performed on the one-dimensional compound Ca
3CoRhO
6. The long-range ordered state was first observed below 90 K. A plateau at 1/3 of the saturation magnetization was observed in the magnetization curve at 70 K, indicating ferrimagnetic alignment of the ferromagnetic Ising chains. We also observed a large hysteresis originating from a spin freezing of ferromagnetic chains in the magnetization curve at 4.2 K. Based on the results of high-field magnetization and neutron diffraction measurements, a possible magnetic structure is discussed in terms of the spin frustration on the triangular lattice.
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Chiaki Uyeda, Takumitsu Komatsu, Makoto Sakakibara, Hiroki Chihara
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1226-1229
Published: 2001
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The magnetic alignment of diamagnetic grains suspended in a gas medium is observed for the first time on micron-sized single crystals of graphite by the use of a system newly developed for this purpose. Previously magnetic alignment was studied on grains suspended in a liquid medium. The field of full orientation H
s at T=293 K was as small as 140 G when the crystal size was 3.5 μm in diameter and 1.0 μm in thickness. It was examined experimentally that the alignment in the gas medium depends on the balance between the thermal agitation energy and the diamagnetic anisotropy energy induced in the particle. This experiment is necessary in order to examine the grain alignment of the interstellar region, which is the basis to observe the interstellar magnetic field. The experiment is necessary also to determine the diamagnetic anisotropy for various inorganic materials through high-temperature measurements.
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Keiji Fukui, Haruhiko Ogasawara, Akio Kotani, Toshiaki Iwazumi, Hirono ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1230-1232
Published: 2001
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We perform theoretical calculations and experimental measurements for magnetic circular dichroism in resonant X-ray emission spectroscopy (MCD-RXES) in Gd
3+ systems. A general expression of MCD-RXES is obtained theoretically for arbitrary directions of incident and emitted X-rays with an atomic model. It is shown that when the incident X-ray is perpendicular to the magnetization of the sample the MCD-RXES originates from the quantum mechanical interference between the excitation and decay processes. The behavior of MCD-RXES calculated for the 2p → 5d excitation and 3d → 2p radiative decay in Gd
3+ is in good agreement with that measured experimentally for a Gd
33Co
67 amorphous alloy.
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Masaharu Isobe, Hisashi Shimizu, Yasuaki Hiwatari
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1233-1236
Published: 2001
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We have performed a multicanonical molecular dynamics simulation on a simple model protein. We have studied a model protein composed of charged, hydrophobic, and neutral spherical bead monomers. Since the hydrophobic interaction is considered to significantly affect protein folding, we particularly focus on the competition between effects of the Coulomb interaction and the hydrophobic interaction. We found that the transition which occurs upon decreasing the temperature is markedly affected by the change in both parameters and forms of the hydrophobic potential function, and the transition changes from first order to second order, when the Coulomb interaction becomes weaker.
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Yoshihiro Ishibashi, Minoru Fukui
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1237-1239
Published: 2001
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The bottleneck effect on one-lane high-speed car traffic is studied. The probability with which cars occupy the sites before and after the bottleneck and the overall flow have been obtained as functions of the probability of opening of a gate located at a point on the lane.
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Zixiang Zhou, Wen-Xiu Ma
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1241-1245
Published: 2001
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The Davey-Stewartson I equation is a typical integrable equation in 2+1 dimensions. Its Lax system being essentially in 1+1 dimensional form has been found through nonlinearization from 2+1 dimensions to 1+1 dimensions. In the present paper, this essentially 1+1 dimensional Lax system is further nonlinearized into 1+0 dimensional Hamiltonian systems by taking the Bargmann constraints. It is shown that the resulting 1+0 dimensional Hamiltonian systems are completely integrable in Liouville sense by finding a full set of integrals of motion and proving their functional independence.
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Yasuaki Narita, Satoru Saito, Noriko Saitoh, Katsuhiko Yoshida
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1246-1255
Published: 2001
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The time evolution of a class of completely integrable discrete Lotka-Volterra system is shown not unique but have two different ways chosen randomly at every step of generation. This uncertainty is consistent with the existence of constants of motion and disappears in both continuous time and ultra discrete limits.
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Jun'ichi Ieda, Takeya Tsurumi, Miki Wadati
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1256-1259
Published: 2001
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Bose-Einstein condensation (BEC) is studied for ideal boson gases with a wide class of the dispersion relations. A criterion of the BEC, the transition temperature and a fraction of the condensate are calculated under the appropriate thermodynamic limits. The correspondence between the dispersion relation (spectrum) and the trap potential is shown. This gives the criterion for the trap shape and the dimensionality of the system.
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Shinji Koga
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1260-1299
Published: 2001
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From a unified point of view, we discuss Birkhoff coordinates of Hamiltonian systems with an external potential including particle-particle interaction owing to N invariant quantities defined in a tangent vector space in autonomous N-dimensional dynamical systems with continuous time. We first consider 2D and 3D billiard systems for a single particle moving under an influence of an arbitrary potential to derive Birkhoff coordinates, and discuss a statistical average of a time between two consecutive collisions against a boundary and a dynamically defined pressure (not a thermodynamical pressure) by assuming that an ergodic measure is realized as a micro-canonical ensemble and moreover almost all trajectories repeat bouncings on the boundary without any trapping by the external potential. We then discuss Birkhoff coordinates for 2D systems for two particles interacting with each other. We also consider 2D and 3D magnetic billiard systems with arbitrary scalar and vector potentials. As illustrative examples, we consider 2D and 3D gravitational billiards, a two particle system with a linear repulsive force to obtain statistical averages of the various quantities defined on the boundary.
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Katsuki Katayama, Tsuyoshi Horiguchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1300-1314
Published: 2001
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We investigate storage capacity and retrieval property for a synchronous fully connected neural network with a non-monotonic transfer function which retrieves sequences of patterns, by an analytic method and also by numerical simulations. Because of asymmetry of interactions and non-monotonicity of the transfer function, it is difficult to use conventional methods of the equilibrium statistical mechanics in order to investigate the network. We then use a generating-function method of path-integral representation, and obtain equations for dynamical order parameters in the stationary state. We clarify that the network with the non-monotonic transfer function retrieves more sequences of patterns than that with a monotonic transfer function at zero temperature when non-monotonicity of the transfer function is selected optimally. It is also clarified that some chaotic behavior appears in solutions for the equations of the dynamical order parameters when non-monotonicity of the transfer function increases. The analytic results are in excellent agreement with the results obtained by numerical simulations.
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Masabumi Miyabe, Masaki Oba, Ikuo Wakaida
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1315-1320
Published: 2001
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Employing three-step resonance ionization mass spectrometry, isotope shift measurements of atomic uranium have been performed in the 32000-36000 cm
-1 and 49950-50500 cm
-1 regions. On the basis of the measured isotope shifts of several autoionizing Rydberg levels, isotopic difference in the ionization potential has been determined to be +445 mK (mK=10
-3 cm
-1).
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Kazuhiro Fuchizaki, Shuichi Sugiyama, Yasuhiko Fujii
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1321-1326
Published: 2001
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Isothermal-isobaric molecular dynamics simulations were carried out for SnI
4 in its liquid state under hydrostatic pressure up to about 5 GPa. The equation of state was obtained from the virial pressure, which was found to be in good agreement with that derived by Boublík regarding a system consisting of hard-convex bodies as a reference fluid. The virial coefficients determined from the equation of state were presented so as to facilitate experimental confirmation.
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Tatsuya Yaguchi, Tsuneya Ando
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1327-1341
Published: 2001
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Scattering of an electron wave at various caps closing an armchair nanotube is studied. The reflection coefficients can be understood as an effective shift in boundary position and phase shift at the boundary. The phase shift is approximately given by π for states with parity + and 0 for states with parity -, respectively. The effective position is approximated by (1/4)P, where P is the height of an equilateral triangle having a base line determined by neighboring five-membered rings located at the boundary between the tube and the cap. The electronic structure of a finite-length armchair nanotube closed by a cap can be calculated with the use of the phase shifts.
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Masatoshi Sato, Masafumi Ito, Hiroshi Harashina, Masaki Kanada, Yukio ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1342-1348
Published: 2001
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In the discussion of the electronic excitation of high T
c Cu oxides, effects of the energy broadening of the quasi particles have to be considered. If it is properly done, data of the tunneling density of states published for Bi
2Sr
2CaCu
2O
8+δ system can provide a clear indication that the pseudo gap observed above T
c can naturally be understood as the precursor of the superconducting gap. The broadening has been taken into account in simple calculations of the magnetic excitation spectra χ
''(q, ω ) of YBa
2Cu
3O
y, with a model which is essentially based on the band picture and includes the exchange coupling among electrons. By comparing the calculated results with observed data, experimental evidence for the quasi particle broadening has been found. Brief arguments are presented if the picture of the dynamical “stripes” which affect the superconductivity works in YBa
2Cu
3O
y.
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Takanobu Jujo
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1349-1363
Published: 2001
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Transport phenomena in the superconducting state are discussed microscopically on the basis of Fermi liquid theory. In this paper we put an emphasis on many body effects. The optical conductivity is shown to have the correction to a current vertex which is explicitly temperature dependent. This current vertex cannot be identified with the velocity of quasiparticles as in the normal state. From these arguments it is concluded that validity of applying results obtained in the normal state simply to the superconducting state is an issue to be carefully studied and not guaranteed in some cases. Several quantities basic in Fermi liquid theory (the renormalization factor, the velocity of quasiparticles and the relation which holds in Galilean invariant case) which have been assumed to hold and given as external parameters in previous works are derived by using Ward-Takahashi identities. These derivations justify the arguments based on the Fermi liquid theory. The many body effect on magnetic field penetration depth is also discussed and an emphasis is put on the difference between this quantity and the superconducting carrier density. By putting together the results obtained for the electromagnetic response case, it is shown that the weight of coherent part which couples to the electromagnetic field is conserved from the normal state to the superconducting state. Thermal conductivity is derived microscopically and the current vertex is shown to be written by the energy current of Bogoliubov quasiparticles. This fact is important for superconductors with anisotropic gaps.
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Koichi Fushimi, Yorihiko Tsunoda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1364-1368
Published: 2001
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Susceptibility and neutron scattering measurements were performed for the giant magnetic moment systems PdCo and PtCo alloys. Short range order of spin modulation wave was observed on the ferromagnetic spin alignment. The results were compared with those observed for other giant magnetic moment systems PdFe and PtFe alloys. A big difference exists for a response to an applied magnetic field probably due to a difference of magnetization easy axes in these systems. A hardness of the saturation magnetization of PdCo alloy would be ascribed to a complex magnetic structure of this system.
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Yoshihiro Takushima, Akihisa Koga, Norio Kawakami
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1369-1374
Published: 2001
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We investigate quantum phase transitions among the spin-gap phases and the magnetically ordered phases in a two-dimensional frustrated antiferromagnetic spin system, which interpolates several important models such as the orthogonal-dimer model as well as the model on the 1/5-depleted square lattice. By computing the ground state energy, the staggered susceptibility and the spin gap by means of the series expansion method, we determine the ground-state phase diagram and discuss the role of geometrical frustration. In particular, it is found that a RVB-type spin-gap phase proposed recently for the orthogonal-dimer system is adiabatically connected to the plaquette phase known for the 1/5-depleted square-lattice model.
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Masaki Mito, Osamu Fujita, Masako Hitaka, Tatsuya Kawae, Kazuyoshi Tak ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1375-1379
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By the measurement of magnetic susceptibility under pressures (P) up to 8 kbar, we investigated pressure effects of the S = 1 Heisenberg antiferromagnetic bond alternating chain compound [{Ni(333-tet)(μ-N
3)}
n](ClO
4)
n (333-tet denotes N,N
'-bis(3-aminopropyl)-1,3-propanediamine), whose alternating interaction ratio (α) at ambient pressure is very close to the theoretical value for the gapless point (α
c ≅ 0.59). There are two kinds of intrachain interactions due to bond alternation (J
1 and J
2), both of which are increased linearly against the pressure. At P = 8 kbar those magnitudes exceed 1.4 times of those at ambient pressure. The magnitude of α ≡ J
2/J
1, however, does not change largely. The normalized magnetic susceptibility χ | J
1|/k
B around k
BT/| J
1| = 0.1 has the maximum value at P = 2 kbar, and this suggests the possibility of the slight changes of α and D.
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Takashi Nakanishi, Shoji Yamamoto, Toru Sakai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1380-1389
Published: 2001
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Quantum and thermal behaviors of low-dimensional mixed-spin systems are investigated with particular emphasis on the design of molecule-based ferromagnets. One can obtain a molecular ferromagnet by assembling molecular bricks so as to construct a low-dimensional system with a magnetic ground state and then coupling the chains or the layers again in a ferromagnetic fashion. Two of thus-constructed quasi-one-dimensional bimetallic compounds are qualitatively viewed within the spin-wave treatment, one of which successfully grows into a bulk magnet, while the other of which ends in a singlet ground state. Then, concentrating on the ferrimagnetic arrangement on a two-leg ladder which is well indicative of general coupled-chain ferrimagnets, we develop the spin-wave theory and fully reveal its low-energy structure. We inquire further into the ferromagnetic aspect of the ferrimagnetic ladder numerically calculating the sublattice magnetization and the magnetic susceptibility. There exists a moderate coupling strength between the chains in order to obtain the most ferromagnetic ferrimagnet.
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Hirotaka Manaka, Isao Yamada, Masakazu Nishi, Tsuneaki Goto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1390-1396
Published: 2001
Released on J-STAGE: February 28, 2003
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At ambient pressure, both the intralayer and the interlayer exchange interactions in the layered compound (CH
3NH
3)
2CuCl
4 are ferromagnetic. Magnetic susceptibility and neutron scattering experiments performed under pressures up to about 1 GPa revealed that the interlayer exchange interaction turns into an antiferromagnetic one at a pressure between 0.41 GPa and 0.61 GPa, while the intralayer exchange interaction remains ferromagnetic. The spin structure in the antiferromagnetic phase is still collinear at least up to 1.1 GPa.
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Yoshiyuki Fukumoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1397-1403
Published: 2001
Released on J-STAGE: February 28, 2003
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Magnetization plateaus in the Shastry-Sutherland model for SrCu
2(BO
3)
2 are studied by the perturbation expansion method. The fourth-order effective Hamiltonian which describes the dynamics of triplet dimers (TD's) with S
totz=1 in the singlet sea is derived and then partially diagonalized for the space that consists of the TD configurations with the lowest second-order energy. The fourth-order terms are treated within a low-density approximation. Our procedure makes clear how TD interactions are responsible for the formation of magnetization plateaus. Particularly, the 1/4-plateau is obtained by the fourth-neighbor TD repulsion in the fourth-order perturbation, and a diagonal stripe arrangement of TD's appears at this plateau.
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Harukazu Kato, Masaki Kato, Kazuyoshi Yoshimura, Koji Kosuge
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1404-1410
Published: 2001
Released on J-STAGE: February 28, 2003
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A mixed valent vanadium compound NaV
6O
11 shows a magnetic phase transition at T
t=245 K. For the microscopic investigation of the transition at T
t,
23Na-NMR measurements from 70 K to 300 K were carried out on NaV
6O
11. The Knight shift, K, and the nuclear spin-lattice relaxation rate, 1/T
1, were measured. While 1/T
1 above T
t has an almost constant value, 1/T
1 below T
t shows a gap-type temperature dependence. This is the first direct evidence that the d-electrons at V(1) ions, which form a kagomé lattice in NaV
6O
11, exhibit a spin-singlet ground state below T
t. The formation of the spin-singlet ground state of V(1) seems to be closely related to the frustration effect.
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Tomozo Tomoyose
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1411-1416
Published: 2001
Released on J-STAGE: February 28, 2003
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We have calculated the transverse effective charge of A
NB
8-N compounds by taking account of the electronic polarization of valence electrons induced by the ionic displacements. It is shown that the transverse effective charge can be expressed as a function of the Phillips ionicity f
i from the relation between the most important pseudopotential and band gaps on the Jones-zone faces for zincblende and rock-salt structures. We have found a critical ionicity F
c that the ionicity dependent transverse effective charge Z
T(f
i) of both structures coincide with together. From the comparison with simple ionic model, the F
c is assigned as identical to the Phillips critical ionicity. We have found that when taking account of the effective valence number based on the modified f-sum rule the Z
T(f
i) well agree with the experimental results for tetrahedrally coordinated compounds. For rock-salt compounds, the two set model of most strongest pseudopotential is qualitatively discussed.
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Norio Akiyama, Shinji Muramatsu, Akifumi Tsuchihashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1417-1421
Published: 2001
Released on J-STAGE: February 28, 2003
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The hot luminescence (HL) spectrum from optically excited F centers nearby thermal equilibrium during lattice relaxation, which is hidden behind an ordinary luminescence (OL) band, has been detected using picosecond time-resolved polarization spectroscopy on KCl. The experimental result is compared with the HL spectrum simulated numerically on the basis of a simple two-level model.
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Yutaka Nishi, Masayoshi Inoue, Toshijiro Tanaka, Moriyasu Murai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1422-1428
Published: 2001
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Explosive volcanic eruptions of Sakurajima, which were observed in 1981-1999, are analyzed where the time interval τ between two successive explosions is considered as a dynamical variable. Correlation dimensions of the time series {τ
i} shows that it can not be regarded as a genuine low-dimensional chaotic time series. The Hurst exponent H of the time series is also calculated, and the result H=0.72 shows that the eruption is not a Poisson process but has persistent behavior.
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Hiroshi Takasaki, Tomotoshi Nishino, Yasuhiro Hieida
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1429-1430
Published: 2001
Released on J-STAGE: February 28, 2003
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Sergey V. Dmitriev, Takeshi Shigenari, Kohji Abe
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1431-1432
Published: 2001
Released on J-STAGE: February 28, 2003
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Junjiro Kanamori, Kiyoyuki Terakura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1433-1434
Published: 2001
Released on J-STAGE: February 28, 2003
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Osamu Narikiyo
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1435-1436
Published: 2001
Released on J-STAGE: February 28, 2003
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Yoshiyuki Matsumoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1437-1438
Published: 2001
Released on J-STAGE: February 28, 2003
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Masami Fujita, Minoru Itoh, Michihiro Horimoto, Yoshiyuki Usuki, Masaa ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 5 Pages
1439-1440
Published: 2001
Released on J-STAGE: February 28, 2003
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