Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 75, Issue 10
Displaying 1-40 of 40 articles from this issue
  • Hayato Shiba, Satoshi Yukawa, Nobuyasu Ito
    2006 Volume 75 Issue 10 Pages 103001
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Heat conduction in three-dimensional nonlinear lattices is investigated using particle dynamics simulations. The system is a simple three-dimensional extension of the Fermi–Pasta–Ulam β nonlinear lattices, in which the interparticle potential has a biquadratic term together with a harmonic term. The system size is L×L×2L, and the heat is made to flow in the 2L direction using the Nosé–Hoover method. Although a linear temperature profile is realized, the ratio of energy flux to temperature gradient shows logarithmic divergence with L. The autocorrelation function of energy flux C(t) is observed to show power-law decay as t−0.98±0.25, which is slower than the decay in conventional momentum-conserving three-dimensional systems (t−3⁄2). Similar behavior is also observed in the four-dimensional system.
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  • Takeshi Matsuo, Yuhei Natsume, Takeo Kato
    2006 Volume 75 Issue 10 Pages 103002
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The thermodynamics of dissipative quantum systems with double-well potentials is studied by a path-integral Monte Carlo (PIMC) method without truncation to the two-state model. For efficient simulation at low temperatures, we develop a new local update scheme on the basis of the approximate decomposition of the Boltzmann weight to Gaussian distributions. The localization transition induced by ohmic dissipation is clarified numerically for arbitrary potential barriers.
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  • Shoji Yamamoto, Toshiya Hikihara
    2006 Volume 75 Issue 10 Pages 103701
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The nuclear spin–lattice relaxation rate 1⁄T1 is calculated for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians. Whether the nearest-neighbor exchange interaction J is ferromagnetic or antiferromagnetic, 1⁄T1 versus temperature T in ring nanomagnets may be peaked at kBT\\simeq|J| provided the lifetime broadening of discrete energy levels is in proportion to T3. Experimental findings for ferromagnetic and antiferromagnetic CuII rings are reproduced with crucial contributions of magnetic anisotropies as well as acoustic phonons.
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  • Wataru Kobayashi, Shin Yoshida, Ichiro Terasaki
    2006 Volume 75 Issue 10 Pages 103702
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Resistivity, thermopower, Hall coefficient, and magnetization are measured for a set of polycrystalline samples of the room-temperature ferromagnet Sr1−xYxCoO3−δ up to 800 K. A peculiar metallic state accompanied by a large effective magnetic moment of 3.40 μB/Co is observed above 600 K, indicating that electrons on the Co3+ ions are magnetic and itinerant. The magnetic Co3+ ions survive at low temperatures, which causes the ferromagnetism below 335 K. We attribute this to the large CoO6 octahedra stabilized in the A-site ordered structure.
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  • Makoto Yokoyama, Hiroshi Amitsuka, Kei Matsuda, Akifumi Gawase, Narumi ...
    2006 Volume 75 Issue 10 Pages 103703
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We performed elastic neutron scattering experiments on solid solution CeRh1−xCoxIn5 with x=0.4 to clarify the nature of the antiferromagnetic (AF) phase in the vicinity of the quantum critical point. We observed the incommensurate AF order below TNh=3.5 K. The structure of the incommensurate AF order is basically unchanged from that for pure CeRhIn5. We further found the evolution of a new commensurate AF order with the modulation of qc=(1⁄2,1⁄2,1⁄2) below TNc=2.9 K. The volume-averaged moments for the incommensurate and commensurate AF phases are 0.38 μB/Ce and 0.21 μB/Ce, respectively, which are reduced from the incommensurate AF moment (0.75 μB/Ce) for pure CeRhIn5. We suggest from these results that the commensurate magnetic correlation may be tightly coupled with the superconductivity observed below Tc=1.4 K.
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  • Annamária Kiss, Yoshio Kuramoto
    2006 Volume 75 Issue 10 Pages 103704
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Phenomenological Landau analysis shows that the properties of ordered phases in some skutterudites are consistently accounted for by a scalar-order parameter which preserves the cubic symmetry, even in the ordered phase. A universal value is found for the anisotropy ratio of the transition temperature in a magnetic field, homogeneous magnetization, and induced staggered magnetization. The difference in magnetic behavior between PrFe4P12 and PrRu4P12 near their phase transitions is explained within a single framework. For the low-field phase of PrFe4P12, the scalar order with Γ1g symmetry can explain (i) the absence of field-induced dipoles perpendicular to the magnetic field, (ii) isotropic magnetic susceptibility in the ordered phase, (iii) the field-angle dependence of the transition temperature, and (iv) the splitting pattern of the 31P nuclear magnetic resonance (NMR) spectra. It is proposed how the order parameter in SmRu4P12 is identified by NMR analysis of a single crystal.
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  • Rei Sakuma, Shinji Tsuneyuki
    2006 Volume 75 Issue 10 Pages 103705
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    A new wavefunction-based method of electronic band structure calculation of solids is proposed based on the transcorrelated (TC) method. In the TC method, a Jastrow–Slater-type correlated wavefunction is used as a trial function. Similarity transformation of the Hamiltonian with respect to the Jastrow correlation function is utilized to derive Hartree–Fock (HF)-like self-consistent-field (SCF) equations, which determine the one-body wavefunctions in the Slater determinant and their orbital energies. Since the electron correlation is taken into account, the method could be a practical tool for band structure calculation of solids where the HF method fails even qualitatively. The single-particle energy dispersion of the electron gas shows no singularity at the Fermi surface due to the screening effect incorporated in the TC method. It is also demonstrated that this method significantly reduces the band gaps of Si, C, and SiC when compared with their corresponding Hartree–Fock values.
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  • Taiya Munenaka, Hirohiko Sato
    2006 Volume 75 Issue 10 Pages 103801
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Single crystals of a novel ruthenate, Ca2Ru2O7, were obtained. An X-ray diffraction study on a single crystal revealed that this material crystallizes in a pyrochlore structure with a lattice parameter, a=10.197 Å. The magnetic susceptibility above 30 K is the summation of a Curie–Weiss contribution and a constant term independent of temperature. The effective moment per Ru atom is only 0.36 μB, one order of magnitude smaller than that expected from a localized spin model with S=3⁄2 for Ru5+. Below 23 K, the localized spins freeze in a spin-glass state. The resistivity at room temperature is 2×10−3 Ω·cm, comparable to that in metallic, highly correlated oxides.
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  • Yuichi Nakamura, Naomichi Hatano
    2006 Volume 75 Issue 10 Pages 104001
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We study a non-Hermitian generalization of quantum systems in which an imaginary vector potential is added to the momentum operator. In the tight-binding approximation, we make the hopping energy asymmetric in the Hermitian Hamiltonian. In a previous article, we conjectured that the non-Hermitian critical point where the energy gap vanishes is equal to the inverse correlation length of the Hermitian system and we confirmed the conjecture for two exactly solvable systems. In this article, we present more evidence for the conjecture. We also argue the basis of our conjecture by noting the dispersion relation of the elementary excitation.
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  • Zhen-Huan Zhang, Ming Deng, Wei-Zhong Zhao, Ke Wu
    2006 Volume 75 Issue 10 Pages 104002
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    By using the prolongation structure theory proposed by Morris, we give a (2+1)-dimensional integrable inhomogeneous Heisenberg Ferromagnet equation, namely, the inhomogeneous Myrzakulov I equation. Through the motion of space curves endowed with an additional spatial variable, its geometrical equivalent counterpart is also presented.
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  • S. Y. Yoon, Yup Kim
    2006 Volume 75 Issue 10 Pages 104003
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    A stochastic discrete growth model which physically corresponds to the drifted Edward–Wilkinson (EW) equation, ∂h⁄∂t=ν∂x2hvxh+η(x,t), is suggested. From the stochastic model with a defect, the height–height correlation function C(r)=⟨|h(x0+r)−h(x0)|⟩ is investigated, where the defect is located at x0. When the surface evolution at the defect is not allowed, C(r) follows the power law C(r)∼rα′ with α′=1⁄4 which is identical to the anomalous roughness exponent α=1⁄4 for the drifted EW equation with a fixed boundary condition. When the surface evolution is partially allowed at the defect, the normal EW behavior is recovered. We also suggest new queuing phenomena based on the asymmetry C(r)≠C(−r) of the correlation function around the perfect defect.
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  • Sawako Tanimoto, Masato Okada, Tomoyuki Kimoto, Tatsuya Uezu
    2006 Volume 75 Issue 10 Pages 104004
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Griniasty et al. introduced an attractor neural network of the temporal cortex based on the correlation-type associative memory model. In this model, there are parameter regions where the Hopfield attractor and the correlated attractor coexist. We study a method of distinguishing these two attractors. For this purpose, we examine the relaxations of neural firing rate fluctuations. In other words, we introduce sublattices and calculate the correlations of firing rate fluctuations in the sublattices using a statistical mechanical method and Monte Carlo simulations. As a result, we found that the relaxation time for the correlated attractor is longer than that for the Hopfield attractor. Therefore, two bistable attractors can be distinguished by observing relaxation times.
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  • D. Singh, M. Afzal Ansari, R. Ali, N. P. M. Sathik, M. Ismail
    2006 Volume 75 Issue 10 Pages 104201
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Complete and incomplete fusion reactions study in heavy ion induced reactions, by 16O ions on 45Sc at incident energies ranging between 39 and 114 MeV have been done using the activation technique followed by γ-ray spectrometry. The excitation functions for eleven reactions have been measured using this technique. A comparison of the experimental data has been made with the calculations based on statistical model. Excitation function measurement of various reactions, for the above projectile–target system is being reported for the first time. Complete and incomplete fusion reaction channels have been identified in the production of various residual nuclei, by analysing the experimental data. The results indicate the occurrence of incomplete fusion involving breakup of 16O into 4He+12C and 8Be+8Be followed by fusion of one of the fragments with target nucleus 45Sc.
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  • Akifumi Yogo, Akio Itoh
    2006 Volume 75 Issue 10 Pages 104301
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Secondary ion emission from a C60-film target was investigated using fast projectile ions of 7Li, 12C, 16O, and 28Si in an energy range from 50 to 300 keV/amu. The measurements were performed by means of time-of-flight mass spectrometry. We observed a variety of fullerene-like ions of C60±2k+ and C60-multiples like C120±2k+. The emission yields of these ions were investigated in terms of the electronic stopping power Se=(dEdx)e to find an appropriate scaling formula. To achieve more accurate scaling formulation, we employed the effective energy deposition derived from a spatial distribution function of energy deposition available in literature. The experimental emission yields have been successfully accounted for by this newly developed quantity.
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  • Masao Takamoto, Feng-Lei Hong, Ryoichi Higashi, Yasuhisa Fujii, Michit ...
    2006 Volume 75 Issue 10 Pages 104302
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We demonstrate a one-dimensional optical lattice clock with a spin-polarized fermionic isotope designed to realize a collision-shift-free atomic clock with neutral atom ensembles. To reduce systematic uncertainties, we developed both Zeeman shift and vector light-shift cancellation techniques. By introducing both an H-maser and a global positioning system (GPS) carrier phase link, the absolute frequency of the 1S0(F=9⁄2)–3P0(F=9⁄2) clock transition of the 87Sr optical lattice clock is determined as 429,228,004,229,875(4) Hz, where the uncertainty is mainly limited by that of the frequency link. The result indicates that the Sr lattice clock will play an important role in the scope of the redefinition of the “second” by optical frequency standards.
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  • Kei Hayashi, Ryuichi Arafune, Shigenori Ueda, Yoichi Uehara, Sukekatsu ...
    2006 Volume 75 Issue 10 Pages 104303
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We have constructed a system for measuring the derivative spectra of very low energy photoelectrons using a lock-in technique. The main advantage of this system lies in determining the energy position of steps in the photoelectron spectra that arise from inelastic scattering of photoelectrons through the excitation of surface vibrational modes. With this system we have measured the derivative spectra of two isotopes, 12C16O and 13C18O adsorbed on Cu(001), and observed the small isotopic shift of ∼1 meV. This result demonstrates that one can precisely determine the vibrational energy of surface adsorbates by using the present measurement system.
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  • Takeru Yano, Ryu Egashira, Shigeo Fujikawa
    2006 Volume 75 Issue 10 Pages 104401
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    One-dimensional linear dispersive waves in water flows containing a number of small spherical air bubbles are analytically studied on the basis of a set of averaged equations recently derived by the present authors. The set of equations consists of the conservation laws for gas and liquid phases and the equation of motion of bubble wall. In addition to the volume-averaged pressure in each phase, the surface-averaged liquid pressure at the bubble wall is incorporated. The compressibility of water is taken into account as well as that of gas in bubbles, and a model of virtual mass force is included, although the Reynolds stress, viscosity, heat conductivity, and the phase change across the bubble wall are disregarded. The results are summarized as follows: (i) the waves are decomposed into the fast mode, slow mode, and convection mode (void wave). (ii) In the uniform flows, the three modes stably exist for all real wave numbers. (iii) In the limit of infinitesimal void fraction, the explicit representation of the elementary solution is obtained. (iv) The instability does not appear in the range where the present averaged equations are applicable.
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  • Takeshi Ogasawara, Sadayoshi Toh
    2006 Volume 75 Issue 10 Pages 104402
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The relative dispersion process in two-dimensional free convection turbulence is investigated by direct numerical simulation. In the inertial range, the growth of relative separation, r, is expected as ⟨r2(t)⟩∝t5 according to the Bolgiano–Obukhov scaling. The result supporting the scaling is obtained with exit-time statistics. Detailed investigation of exit-time PDF shows that the PDF is divided into two regions, the Region-I and -II, reflecting two types of separating processes: persistent expansion and random transitions between expansion and compression of relative separation. This is consistent with the physical picture of the self-similar telegraph model. In addition, a method for estimating the parameters of the model are presented. Comparing two turbulence cases, two-dimensional free convection and inverse cascade turbulence, the relation between the drift term of the model and nature of coherent structures is discussed.
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  • Shinichiro Toda, Kimitaka Itoh, Klaus Hallatschek, Masatoshi Yagi, San ...
    2006 Volume 75 Issue 10 Pages 104501
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The nonlinear dynamics of coherent zonal flows is studied with periodic boundary conditions. We study nonlinear differential equations of zonal flows, which were previously derived in an analytic wave-kinetic model. Competition between the short wavelength zonal flow and the long wavelength zonal flow is studied. Although many stable stationary solutions are allowed, the radial periodicity length turns out to be a value around a particular length, when random small amplitude perturbations are chosen as the initial flow state.
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  • Yosuke Kawai, Yasuhito Kiwamoto, Kiyokazu Ito, Akio Sanpei, Yukihiro S ...
    2006 Volume 75 Issue 10 Pages 104502
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Experimentally observed dynamics of vortex patches, as generated by the diocotron instability in a magnetized pure electron plasma, is examined in terms of the power spectra of the distributions of particles and flux, and the energy spectrum. The global pattern of the azimuthal-flux in the initial ring distribution is torn into mesoscopic blobs with local circulation at the cost of the reduction of the energy in the radial shear of the azimuthal flow. In a turbulent stage characterized by mergers between the blobs, the energy spectrum broadens upward in the wave-number space while the dominant mode shifts downward in such a way as is consistent with a cascade model of the turbulence theory. The rapid relaxation is accompanied by the reduction of enstrophy and enters a slow process whereby a symmetric pattern of the azimuthal flow emerges in a convex profile. Until the asymptotic state, the energy and the angular momentum of the whole plasma system remain conserved but the radial shear is substantially reduced. The spectra in the final state concentrate at symmetric modes with a slight contribution from the orbiting motion of the plasma column. From these experimental results, a picture of the turbulent relaxation involving the vortex dynamics covering wide length scales is given in the wave-number space, which has previously not been pursued with regard to pure electron plasmas.
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  • Mamoru Yamashita, Masashi Torikai
    2006 Volume 75 Issue 10 Pages 104601
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Nematic order is usually described by a uniaxial order parameter, or occasionally by a biaxial order parameter together with the uniaxial one, in a typical configuration. In a general case of a system exposed to two different types of external fields, e.g., an electric field and a magnetic field, an additional order parameter, here called an oblique axial order parameter, is shown to be necessary, in addition to the above order parameters, to describe transition phenomena of the system correctly. The symmetry of the phase with the triplet of the order parameters is discussed. Effect of the oblique axial order are demonstrated practically in two phenomena: (i) qualitative change of the phase transition when the oblique axial order is neglected; (ii) disappearance of phase transition between ordered phases with different ordering axes when an oblique axial field conjugate to the oblique axial order parameter exists.
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  • Salah A. M. El Shourbagy, Shinichi Morita, Hans-Georg Matuttis
    2006 Volume 75 Issue 10 Pages 104602
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We investigate the effect of particle shape and interparticle friction on the stress–strain-relation using the discrete element method (DEM) in two dimensions. Elongated particles show a significantly higher shear strength than non-elongated particles. The relative maximum which is characteristic for experimental stress–strain curves of granular materials is found only for elongated particles with finite Coulomb friction, which indicates that the particle elongation is an important parameter in the statistical physics of granular materials. An earlier simulation result from another group which showed a maximum for non-elongated particles could be identified to be due to the formation of a shear band.
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  • Yuki Nagai, Yosuke Ueno, Yusuke Kato, Nobuhiko Hayashi
    2006 Volume 75 Issue 10 Pages 104701
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    On the basis of the quasiclassical theory of superconductivity, we obtain a formula for the local density of states (LDOS) around a vortex core of superconductors with anisotropic pair-potential and Fermi surface in arbitrary directions of magnetic fields. Earlier results on the LDOS of d-wave superconductors and NbSe2 are naturally interpreted within our theory geometrically; the region with high intensity of the LDOS observed in numerical calculations turns out to the enveloping curve of the trajectory of Andreev bound states. We discuss experimental results on YNi2B2C within the quasiclassical theory of superconductivity.
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  • Hiori Kino, Hiroshi Kontani, Tsuyoshi Miyazaki
    2006 Volume 75 Issue 10 Pages 104702
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We study the electronic structure of β′-(BEDT-TTF)2AuCl2 under hydrostatic pressures of up to 20 GPa. We employ the effective single-band Hubbard model, the band structure of which is based on the first-principles result, and apply the FLEX approximation to take into account of the effective on-site Coulomb interaction. We examine magnetic and superconducting instabilities to find that the resulting theoretical phase diagram shows that the Néel temperature is high under hydrostatic pressure. In contrast to β′-(BEDT-TTF)2ICl2, β′-(BEDT-TTF)2AuCl2 is expected to show no superconducting state.
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  • Yoshihiko Kobayashi, Takaaki Mogi, Kichizo Asai
    2006 Volume 75 Issue 10 Pages 104703
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We have investigated the crystalline structure and the magnetic properties of La1−xPrxCoO3 single crystals. The crystalline symmetry is rhombohedral R\\bar3c for 0≤x≤0.3, and orthorhombic Pnma for 0.7≤x≤1. The lattice volume decreases monotonically with increasing Pr content due to the smaller ionic radius of Pr3+ than La3+. The temperature dependence of the magnetic susceptibility [χ(T)] arising from Co3+ ions in La1−xPrxCoO3 was evaluated using La1−xPrxAlO3 as a reference. The temperature dependence of the effective magnetic moment arising from Co ions is interpreted by the three spin-states low-spin (LS), intermediate-spin (IS) and high-spin (HS). The energy of the IS-state (Δ1) increases with increasing Pr content through the chemical pressure. The chemical pressure dependence of Δ1 agrees with the hydrostatic pressure dependence. In contrast to the first spin-state transition, the second spin-state transition is almost independent of the Pr content.
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  • Kazuko Zenmyo, Hidenori Kubo, Masahiko Tokita, Kazuo Yamagata
    2006 Volume 75 Issue 10 Pages 104704
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    In nickel formate di-hydrate, Ni(HCOO)2·2H2O, there are two nonequivalent Ni sites forming two magnetic subsystems, A- and B-layers. Heat capacity measurements suggest that the Ni ions in the B-layer are paramagnetic even below TN and the Ni ions in the A-layer are in antiferromagnetic order. On the other hand, the magnetization suggests the weak ferrimagnetic order of Ni ions in both A- and B-layers. To solve the inconsistency above, the spin system is investigated by proton NMR. The observed resonance frequencies are compared with calculations based on various magnetic structures. The comparison shows that the ferrimagnetic spins order with canting magnetic moments in the ab plane. The magnitude of the magnetic moment of B-ions, 0.38μ0, is much smaller than that of A-ions, 2.38μ0, where μ0 is the Bohr magneton. It is inferred that the paramagnetic B-ions are pulled into the antiferromagnetic order by the dipolar field due to A-ions. The magnetic moments are inferred to gradually incline parallel to the c-axis with increasing temperature.
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  • Chitoshi Yasuda, Daisuke Kinouchi, Kenn Kubo
    2006 Volume 75 Issue 10 Pages 104705
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We study the spin wave in the S=1⁄2 multiple-spin exchange model on a triangular lattice in a magnetic field within the linear spin-wave theory. We take only two-, three-, and four-spin exchange interactions into account and restrict ourselves to the region where a coplanar three-sublattice state is the mean-field ground state. We found that the Y-shape ground state survives quantum fluctuations and the phase transition to a phase with a 6-sublattice structure occurs with softening of the spin wave. We estimated the quantum corrections to the ground state sublattice magnetizations due to zero-point spin-wave fluctuations.
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  • Kohji Kamada
    2006 Volume 75 Issue 10 Pages 104706
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    This paper deals with the theoretical explanation of the experimental results reported in previous papers, demonstrating the anomalous melting of an Al surface layer upon energetic electron bombardment during electron microscopic observation, when the Al surface layer contains large-scale deuterium precipitates. The theory is based on the spin-flip-phonon-maser action of deuteron nucleus in a strong magnetic field as previously reported to explain the heating of heavy water on acoustic wave propagation, and gives large enough energy to explain the melting.
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  • Takuo Ohkochi, Ko Mibu, Nobuyoshi Hosoito
    2006 Volume 75 Issue 10 Pages 104707
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The depth distribution of the induced spin polarization in the Au layers of epitaxitial Fe/Au(001) superlattices has been estimated by resonant X-ray magnetic scattering, using circularly polarized X-rays near the Au L3 absorption edge. It is suggested by precise analysis that Au spin polarization has itinerant character and is distributed uniformly to the middle of each Au layer. Oscillations in the sign of the spin polarization, which are expected or believed from the oscillations of exchange coupling constant J as a function of spacer layer thickness, are not found in the depth distribution.
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  • Minoru Soda, Yukio Yasui, Yoshiaki Kobayashi, Toshiaki Fujita, Masatos ...
    2006 Volume 75 Issue 10 Pages 104708
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    NMR studies have been carried out on a single-crystal sample of TbBaCo2O5.5 with an oxygen-deficient perovskite structure. We have also carried out neutron diffraction studies and added new results to our previously published data. By analyzing these data, the magnetic structures and the spin states of the system, which have been the subjects of strong controversy, are argued in the ferromagnetic and antiferromagnetic phases. We show that among the various magnetic structures that have been proposed, only our noncollinear structures can reproduce all the experimental results accumulated up to now.
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  • Takanobu Jujo
    2006 Volume 75 Issue 10 Pages 104709
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We discuss some properties of the nonlinear absorption spectrum of insulators with a gap originating from the electron correlation. We formulate a method of evaluating the nonlinear susceptibility and apply this to the antiferromagnetic insulator. A scaling relation for two-photon absorption is derived and applied to a quantitative estimation, which gives values comparable to those of experiments on Mott insulators. The direct transition term is found to be dominant in many-body systems. It is also shown that our formulation naturally includes the final-states interaction (the charge fluctuation and the excitonic effect), which gives a sufficient contribution to the two-photon absorption spectrum.
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  • F. L. Shyu, C. C. Tsai, M. F. Lin, C. C. Hwang
    2006 Volume 75 Issue 10 Pages 104710
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Electronic states of carbon tori in electric and magnetic fields are studied by the tight-binding model with the curvature effect. Electronic properties, such as electronic states, energy gaps, and density of states, are very sensitive to the changes in the direction and the magnitude of the external fields. The electric field can widen the π-electron energy width; furthermore, there are more low- and extreme-energy states. Energy gaps are drastically modulated by E. The zero-gap transition (Eg≠0→Eg=0) happens more frequently when E deviates from the symmetric axis, or its magnitude is sufficiently large. The electric field could change the state degeneracy. Moreover, the modulation of electronic states is enhanced by the magnetic field.
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  • Oleg Derzhko, Taras Verkholyak
    2006 Volume 75 Issue 10 Pages 104711
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We consider the spin-1⁄2 isotropic XY chain in a (z) transverse magnetic field with the Dzyaloshinskii–Moriya interaction directed along the z-axis in spin space and examine the effects of the latter interaction on the zz, xx (yy) and xy (yx) dynamic structure factors. The Dzyaloshinskii–Moriya interaction does not manifest itself in the zz dynamic quantities. In contrast, the xx (yy) and xy (yx) dynamic structure factors show dramatical changes owing to the Dzyaloshinskii–Moriya interaction. Implications of our results for electron spin resonance experiments are briefly discussed.
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  • Shogo Shinkai, Hiroaki Ikeda, Kosaku Yamada
    2006 Volume 75 Issue 10 Pages 104712
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We investigate the mass enhancement factor and the superconducting transition temperature Tc in the d–p model, to explain differences of Tc observed in the high-Tc cuprates, such as YBa2Cu3O7−δ (YBCO) and La2−xSrxCuO4 (LSCO). First, we calculate the mass enhancement factor by expanding the normal selfenergy perturbatively up to the fourth order with respect to the on-site repulsion U. The large mass enhancement is obtained when the energy level splitting between the d-level and the p-level is large, which corresponds to LSCO. Next, we calculate Tc by expanding the effective pairing interaction up to the third order and solving the Éliashberg equation in the renormalized quasiparticle scheme. As results, Tc is remarkably suppressed due to the large mass renormalization factor when the level splitting is large. We conclude that the strong correlation in LSCO enhances the pairing interaction but reduces the quasiparticle energy scale more efficiently, and then Tc in LSCO is lower than that in YBCO.
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  • N. Hanasaki, K. Masuda, K. Kodama, M. Matsuda, H. Tajima, J. Yamazaki, ...
    2006 Volume 75 Issue 10 Pages 104713
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We investigated the ground state of a highly one-dimensional conductor, TPP[Co(Pc)(CN)2]2 (TPP = tetraphenylphosphonium and Pc = phthalocyanine), by the measurement of the X-ray diffraction, electron spin resonance, nuclear quadrupole resonance, and magnetoresistance. An increase of the magnetic fluctuations was observed below 20 K, where no structural deformation was detected. In the 59Co nuclear quadrupole resonance, we found an asymmetric broadening of the spectra owing to the intrinsic inhomogeneity of the molecular charge. We propose that the ground state is characterized by a weak charge disproportionation with antiferromagnetic fluctuations due to the high one dimensionality. A large magnetoresistance was observed under a high magnetic field. Spin effects are dominant at low fields. The anisotropic magnetoresistance suggests a change in the ground-state nature above 10 T.
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  • Rie Y. Umetsu, Kazuaki Fukamichi, Akimasa Sakuma
    2006 Volume 75 Issue 10 Pages 104714
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    The electrical resistivity, magnetic and low-temperature specific heat measurements, and theoretical calculations for L10-type MnPd alloy system were carried out in a wide range of composition from 40 to 60% Pd. In the present antiferromagnetic alloy system, the highest Néel temperature TN was observed in the vicinity of 53% Pd concentration, deviating from the equiatomic concentration. This behavior was also conformed by the theoretical calculations for the effective exchange constant J0 which gives the value of TN. In the temperature dependence of electrical resistivity for the L10-type MnPd alloys, a characteristic behavior of a hump just below TN was observed, which is associated with the pseudo-gap-type antiferromagnets. In addition, the value of the electronic specific heat coefficient γe is significantly small below 1 mJ mol−1 K−2 above 50% Pd, reflecting the very low density of states at the Fermi energy EF. The linear relation between the magnetic moment and the Pauling valence has been confirmed in the L10-type Mn alloy systems, together with that of other Mn alloy systems. The present several results strongly imply that the characteristic electronic structure with the pseudo-gap and the Pauling valence (PV) associated with the covalent bonding state is closely interrelated in the L10-type Mn alloy systems.
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  • Shuichi Kawamata, Toshikazu Kizawa, Takahiro Suzuki, Eiichi Negishi, H ...
    2006 Volume 75 Issue 10 Pages 104715
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    Electron spin resonance experiments with 15.4 GHz microwave have been performed on λ-(BEDT-TSF)2Fe1−xGaxCl4 (x=0.0, 0.4, and 1.0) single crystals at various temperatures down to 1.5 K, where BEDT-TSF denotes bis(ethylenedithio)tetraselena-fulvalene. For λ-(BEDT-TSF)2GaCl4, the resonance signal due to π-electrons at the BEDT-TSF molecule layer is observed. For λ-(BEDT-TSF)2Fe0.6Ga0.4Cl4, signals which originate both from π-electrons at the BEDT-TSF molecule layer and from d-electrons at Fe ions are observed. For λ-(BEDT-TSF)2FeCl4, only one resonance signal is observed. The magnetic field direction dependencies of the g-value do not show the symmetry of the conducting ac-plane above 20 K. This means that the observed signals are not mainly due to the π-electrons at the BEDT-TSF molecule layer but due to the d-electrons at Fe ions. The resonance due to the π-electrons is expected to be renormalized by the strong correlation between the π- and d-electrons. The anomaly has been observed in the g-value as well as the line width both for λ-(BEDT-TSF)2FeCl4 at around 70 K and for λ-(BEDT-TSF)2Fe0.6Ga0.4Cl4 at around 95 K. This might be correlated to the dielectric and structural anomaly observed for λ-(BEDT-TSF)2FeCl4.
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  • Shintaro Ishiwata, Ichiro Terasaki, Yoshihiro Kusano, Mikio Takano
    2006 Volume 75 Issue 10 Pages 104716
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We report on the measurements and analyses of resistivity, Hall coefficient, and thermopower of the misfit-layered compound, [Sr2O2−δ]pCoO2, using single-crystalline samples obtained by a high-pressure technique. Using a polycrystalline sample, magnetic susceptibilities are measured to roughly characterize the electronic states of the cobalt ions. The misfit ratio, p, was determined to be 0.53 from transmission electron microscopic analyses. [Sr2O2−δ]0.53CoO2 shows metallic conduction down to 2 K and Curie–Weiss-like susceptibility as Na0.75CoO2 does. In addition, the thermopower at room temperature is the smallest among the known misfit-layered cobalt oxides, though the carrier concentration is almost the same as that of the misfit-layered compound, Ca3Co4O9, which has a much larger thermopower. We discuss the room-temperature thermopower in misfit-layered cobalt oxides from the viewpoint of incommensurability-induced anisotropy which changes the density of states near the Fermi level.
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  • Montri Phothisonothai, Masahiro Nakagawa
    2006 Volume 75 Issue 10 Pages 104801
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    In this paper proposes the classification method of new imagery tasks for simple binary commands approach to a brain–computer interface (BCI). An analysis of imaginary tasks as “yes/no” have been proposed. Since BCI is very helpful technology for the patients who are suffering from severe motor disabilities. The BCI applications can be realized by using an electroencephalogram (EEG) signals recording at the scalp surface through the electrodes. Six healthy subjects (three males and three females), aged 23–30 years, were volunteered to participate in the experiment. During the experiment, 10-questions were used to be stimuli. The feature extraction of the event-related synchronization and event-related desynchronization (ERD/ERS) responses can be determined by the slope coefficient and Euclidian distance (SCED) method. The method uses the three-layer feedforward neural network based on a simple backpropagation algorithm to classify the two feature vectors. The experimental results of the proposed method show the average accuracy rates of 81.5 and 78.8% when the subjects imagine to “yes” and “no”, respectively.
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  • Isamu Sakai, Yoshinori Hayakawa
    2006 Volume 75 Issue 10 Pages 104802
    Published: October 15, 2006
    Released on J-STAGE: August 27, 2009
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    We carried out experiments on the collective crystal growth of sucrose into a form of candy known as Kompeitoh. We examined the process for the selection of granule size and the number of spikes formed on the crystal surface. We found that the characteristic size of spikes was proportional to the size of granules in the steady-state regime, although the proportionality coefficient was dependent on conditions such as the initial shape of the crystals. A selection process of surface structure during the crystallization appears to have been caused by the distribution process of sucrose solution during the mixing of granules. In addition, a phenomenological model of surface growth based on the obtained experimental results is presented herein.
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