Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 77, Issue 10
Displaying 1-50 of 51 articles from this issue
  • Hiroshi Watanabe
    2008 Volume 77 Issue 10 Pages 103001
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    A Langevin equation with state-dependent random force is considered. When the Helmholtz free energy is a nonincreasing function of time (the H-theorem), a generalized Einstein relation is obtained. A stochastic process of the Nosé–Hoover method is discussed on the basis of the Markovian approximation. It is found that the generalized Einstein relation holds for the Fokker–Planck equation associated with the stochastic Nosé–Hoover equation. The present result indicates that the Nosé–Hoover dynamics coarse-grained with time satisfies the H-theorem and therefore the canonical distribution is guaranteed for the subsystem.
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  • Ryo Tamura, Naoki Kawashima
    2008 Volume 77 Issue 10 Pages 103002
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We study a finite-temperature phase transition in the two-dimensional classical Heisenberg model on a triangular lattice with a ferromagnetic nearest-neighbor interaction J1 and an antiferromagnetic third-nearest-neighbor interaction J3 using a Monte Carlo method. Apart from a trivial degeneracy corresponding to O(3) spin rotations, the ground state for J3≠0 has a threefold degeneracy corresponding to 120° lattice rotations. We find that this model exhibits a first-order phase transition with the breaking of the threefold symmetry when the interaction ratio is J3J1=−3.
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  • Kentaro Goto, Fumihiko Matsui, Tomohiro Matsushita, Yukako Kato, Hiros ...
    2008 Volume 77 Issue 10 Pages 103301
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Two-dimensional angular distribution patterns of Fe 3p and 3d photoelectrons from an Fe(111) surface were measured using circularly polarized soft X-ray at SPring-8. The circular dichroism of rotational shift in forward focusing peaks (FFPs) around the incident-light axis was observed. Shifts of the FFPs in the [111], {110}, and {100} directions were inversely proportional to the distances between the emitter and neighboring atoms in the corresponding directions. These shifts correspond to the parallax in the stereograph of the atomic arrangements. We found that the orbital angular momentum of a valence band can be deduced precisely from the ratio of forward focusing peak shifts between 3p and 3d. The orbital angular momenta of 3d valence electrons are found to be almost equally distributed from −2 to 2.
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  • Takeshi Matsumura, Toshiya Inami, Masashi Kosaka, Yoshiaki Kato, Takak ...
    2008 Volume 77 Issue 10 Pages 103601
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The unresolved phase transition at 80 K in YbAl3C3 has been studied by X-ray diffraction. It has been confirmed that the transition is a structural one with atomic displacement. Superlattice reflections that appear below 80 K show that the crystal structure changes from hexagonal to orthorhombic. From the reflection conditions, we conclude that the space group in the low temperature phase is Pbca, where all the atoms occupy the general 8c site. By fitting the observed intensities, we present two possible models of atomic displacement. The displacement results in the deformation of the triangular lattice of Yb spins, which is considered to be responsible for the formation of a spin-singlet ground state at low temperatures.
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  • Yoshikazu Ito, Akira Miyazaki, Ken-ichi Fukui, Suresh Valiyaveettil, T ...
    2008 Volume 77 Issue 10 Pages 103701
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Single molecular magnets and single-particle magnets have been intensively investigated from the viewpoints of spintronics devices. We employ the giant magnetic moment effect on magnetic impurities embedded in Pd in designing a single-nanoparticle magnet. A transition metal magnetic impurity such as Co has a giant magnetic moment in Pd metal due to the exchange enhancement effect. As the interaction range of the effect is ca. 1 nm from the magnetic impurity center, all Pd atoms are spin-polarized in a Pd nanoparticle having a radius smaller than the range. Here, we unveil this feature experimentally and show that a Pd nanoparticle containing only one Co atom exhibits a single-domain nanomagnet behavior with a blocking temperature of 3 K.
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  • Vladimir P. Mineev
    2008 Volume 77 Issue 10 Pages 103702
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The symmetry approach to the description of the (P,T) phase diagram of ferromagnet superconductors with triplet pairing is developed. Taking into account the recent experimental observations made on UCoGe the case of a crystal with orthorhombic structure and strong spin–orbital coupling is considered. It is shown that formation of a ferromagnet superconducting state from a superconducting state is inevitably accompanied by first-order-type transition.
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  • Soshi Takeshita, Ryosuke Kadono, Masatoshi Hiraishi, Masanori Miyazaki ...
    2008 Volume 77 Issue 10 Pages 103703
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The presence of macroscopic phase separation into superconducting and spin-glass-like magnetic phases in LaFeAs(O1−xFx) is demonstrated by muon spin rotation measurement in a sample near the phase boundary (x=0.06). Both magnetism and superconductivity develop simultaneously below a common critical temperature, Tm\\simeqTc\\simeq18 K. This remarkable accordance strongly suggests that the electronic correlations leading to these two competing ground states share a common origin.
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  • Ayaka Kawabata, Sang Chul Lee, Taketo Moyoshi, Yoshiaki Kobayashi, Mas ...
    2008 Volume 77 Issue 10 Pages 103704
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have prepared the superconducting system LaFe1−yCoyAsO1−xFx (x=0.11) and carried out measurements of their electrical resistivity ρ and superconducting diamagnetism. 75As- and 135La-NMR studies have also been carried out. The Knight shift observed for 75As has been found to be suppressed by the superconductivity; for 135La, the shift is almost insensitive to the superconductivity. This result presents rather strong experimental evidence for singlet pairing. The Co doping effect on the superconducting transition temperature Tc is not so significant as expected for superconductors with nodes, suggesting that the potential scattering does not seem to primarily suppress the superconductivity. Even for superconductors without nodes, it may not be so trivial to expect this small effect, if there are two different (disconnected) Fermi surfaces whose order parameters have opposite signs. As a possible explanation of the observed Tc suppression, which is found to be small, seems to be related with the loss of the itinerant nature of the electrons.
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  • Fanlong Ning, Kanagasingham Ahilan, Takashi Imai, Athena S. Sefat, Ron ...
    2008 Volume 77 Issue 10 Pages 103705
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report an NMR investigation of the superconductivity in BaFe2As2 induced by Co doping (Tc=22 K). We demonstrate that Co atoms form an alloy with Fe atoms and donate carriers without creating localized moments. Our finding strongly suggests that the underlying physics of iron–pnictide superconductors is quite different from the widely accepted physical picture of high Tc cuprates as doped Mott insulators. We also show a crossover of electronic properties into a low temperature pseudo-gap phase with a pseudo-gap ΔPGkB∼560 K, where χspin∼constant and resisitivty ρ∝T. The NMR Knight shift below Tc decreases for both along the c-axis and ab-plane, and is consistent with the singlet pairing scenario.
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  • Shinji Kitao, Yasuhiro Kobayashi, Satoshi Higashitaniguchi, Makina Sai ...
    2008 Volume 77 Issue 10 Pages 103706
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    57Fe Mössbauer spectroscopy was applied to an iron-based layered superconductor LaFeAsO0.89F0.11 with a transition temperature of 26 K and to its parent material LaFeAsO. Throughout the temperature range from 4.2 to 298 K, a singlet pattern with no magnetic splitting was observed in the Mössbauer spectrum of the F-doped superconductor. Furthermore, no additional internal magnetic field was observed for the spectrum measured at 4.2 K under a magnetic field of 7 T. On the other hand, magnetically split spectra were observed in the parent LaFeAsO below 140 K, and this temperature is slightly lower than that of a structural phase transition from tetragonal to orthorhombic phase, which accompanies the electrical resistivity anomaly at around 150 K. The magnetic moment is estimated to be ∼0.35 μB/Fe from the internal magnetic field of 5.3 T at 4.2 K in the orthorhombic phase, and the spin disorder appears to remain in the magnetically ordered state even at 4.2 K. The lack of a magnetic transition in LaFeAsO0.89F0.11 down to 4.2 K suggests that this system exhibits a paramagnetic state or that the magnetic moment is small. The present results show that F doping effectively suppresses the magnetic and structural transitions in the parent material, leading to the emergence of superconductivity in the F-doped system.
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  • Kenji Hirano, Tomoe Fukamachi, Masami Yoshizawa, Riichirou Negishi, Ke ...
    2008 Volume 77 Issue 10 Pages 103707
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    X-ray interference fringes in diffraction beam from side surface of a thin plane-parallel crystal in Bragg–(Bragg)m–Laue case are measured and analyzed by using Wagner’s approach. The origin of the interference fringes is explained by interference between the diffraction beam in Bragg–Laue case and that in Bragg–Bragg–Laue case. A part of the beams from side surface cannot be explained by the interference effect, but can be explained by the effect of confined beam.
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  • Bin Chen, Chishiro Michioka, Yutaka Itoh, Kazuyoshi Yoshimura
    2008 Volume 77 Issue 10 Pages 103708
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The itinerant-electron ferromagnet Ni3Al and its carbon-intercalated compounds Ni3AlCx (x=0.01, 0.02, 0.04, 0.05, 0.08, and 0.1) were synthesized and investigated by magnetization measurements between 2 and 300 K with the magnetic field H up to 5 T and 27Al NMR measurements at H=7.4847 T. The Curie temperature is suppressed and disappears only by the carbon intercalation with x=0.02. For the samples with x≤0.02, the T4⁄3-temperature dependence of Ms2 (Ms: spontaneous magnetization) and χ0−10: initial susceptibility) are newly observed, being consistent with the predication of the self-consistent renormalization theory of spin fluctuations for weak itinerant ferromagnets. The coupling constant between the 27Al Knight shift and the bulk susceptibility of Ni3AlC0.1 is three times larger than that of Ni3Al, suggesting the drastic change of the electronic state by the carbon intercalation.
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  • Dariusz Wardecki, Radoslaw Przenioslo, Izabela Sosnowska, Yurii Skours ...
    2008 Volume 77 Issue 10 Pages 103709
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The magnetization of polycrystalline ceramic BiFeO3 has been studied with pulsed magnetic fields up to 58 T. We observe a magnetic transition in both, increasing and decreasing magnetic fields. The critical field of the transition decreases with temperature. It is observed at 18.1 T at 80 K and 16.1 T at 235 K for increasing fields, whereas with decreasing fields the transition is observed at about 1.5 T below these values. The observed transition is the same as that reported in BiFeO3 single crystals at 10 K [Kadomtseva et al.: JETP Lett. 79 (2004) 571]. It was attributed to the destruction of the modulated magnetic ordering in BiFeO3.
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  • Atsushi Harada, Hidekazu Mukuda, Yoshio Kitaoka, Arumugam Thamizhavel, ...
    2008 Volume 77 Issue 10 Pages 103710
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report a 73Ge nuclear-quadrupole-resonance (NQR) study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the 73Ge-NQR spectrum and the nuclear spin–lattice relaxation rate (1⁄T1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Néel temperature TN exhibits its maximum at 8.5 K. The superconducting transition temperature TSC has been found to be enhanced with increasing TN, before reaching the quantum critical point at which the AFM order collapses. Above TSC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T∼2 K, accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the PT phase diagram.
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  • Takashi Hotta
    2008 Volume 77 Issue 10 Pages 103711
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    By employing a numerical renormalization group technique, we evaluate electronic specific heat coefficient γ of the Anderson model coupled with local anharmonic phonons for the oscillation of a caged atom. For the rattling-type cage potential with a flat and wide region in the bottom, we find that phonon-mediated attraction is largely enhanced. When the potential shape is deformed from the rattling type, there occurs a cancellation between Coulomb repulsion and the phonon-mediated attraction. In such a situation, spin and charge fluctuations are comparable to each other, leading to the realization of exotic electron–phonon complex state with large and magnetically robust γ.
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  • Yoshihiro Aiura, Koji Sato, Hideaki Iwasawa, Yosuke Nakashima, Hiroaki ...
    2008 Volume 77 Issue 10 Pages 103712
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Photoemission spectroscopy with low-energy tunable photons on oxygen-deficient iron-based oxypnictide superconductors NdFeAsO0.85 (Tc=52 K) reveals a distinct photon-energy dependence of the electronic structure near the Fermi level (EF). A clear shift of the leading-edge can be observed in the superconducting states with 9.5 eV photons, while a clear Fermi cutoff with little leading-edge shift can be observed with 6.0 eV photons. The results are indicative of the superconducting gap opening not on the hole-like ones around Γ(0,0) point but on the electron-like sheets around M(π,π) point.
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  • Yuichi Ito, Kazunari Matsuda, Yoshihiko Kanemitsu
    2008 Volume 77 Issue 10 Pages 103713
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report reversible and irreversible spectral changes during the photoluminescence (PL) blinking of single CdSe/ZnS core/shell semiconductor nanocrystals on glass and gold substrates. Under prolonged intense light illumination, time traces of spectrally resolved PL can be classified into reversible and irreversible periods before the PL is completely quenched. During the irreversible PL blinking period, very large spectral shifts occur during on times and after off times, compared with the reversible PL period. The clear blueshift of the PL peak energy is also observed on glass and gold substrates in air. The PL blinking mechanism and photodegradation of nanocrystals are discussed in light of the spectral shift during PL blinking.
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  • Philip M. R. Brydon, Dirk Manske, Manfred Sigrist
    2008 Volume 77 Issue 10 Pages 103714
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We study the appearance of a Josephson spin current in a model triplet superconductor junction with a magnetically-active tunneling barrier. We find three distinct mechanisms for producing a spin current, and we provide a detailed discussion of the symmetry properties and the physical origins of each. By combining these three basic mechanisms, we find that it is possible to exercise fine control over the spin currents. In particular, we show that unlike the charge current, the spin currents on either side of the barrier need not be identical.
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  • Tatsuo Fukuda, Alfred Q. R. Baron, Shin-ichi Shamoto, Motoyuki Ishikad ...
    2008 Volume 77 Issue 10 Pages 103715
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The lattice dynamics of LaFeAsO1−xFx (x=0,0.1) and PrFeAsO1−y (y∼0.1) are investigated using inelastic x-ray scattering and ab-initio calculation. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO1−y. A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by reducing the strength of the Fe–As bond by 30%.
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  • Yukito Iba, Koji Hukushima
    2008 Volume 77 Issue 10 Pages 103801
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The idea of rare-event sampling by the multicanonical Monte Carlo is applied to the estimation of the performance of error correcting codes. The essence of the idea is importance sampling of the pattern of noise in the channel by the multicanonical Monte Carlo, which enables efficient estimation of the tails of the distribution of bit errors. The proposed method is successfully tested with a convolutional code.
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  • Akira Shimizu
    2008 Volume 77 Issue 10 Pages 104001
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    For a multi-component system, general formulas are derived for the dimension of a coexisting region in the phase diagram in various state spaces.
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  • Kutsal Bozkurt
    2008 Volume 77 Issue 10 Pages 104201
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The dipole response function of nuclear matter at finite temperature is investigated by employing a linearized Landau–Vlasov equation with pairing correlations. We calculate the giant dipole resonance strength function with and without quasiparticle collisional effects. Calculations are carried out for nuclear dipole vibrations of finite nuclei by employing the Steinwedel–Jensen model, and their results are compared with experimental results for 120Sn.
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  • Su-Hui Liang, Jia-Hao Li, Bai-Xin Liu
    2008 Volume 77 Issue 10 Pages 104301
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    An n-body potential of the Cu–Zr system is constructed under the formalism of the second moment approximation of tight-binding. Applying the proven relevant Cu–Zr potential, solid-state amorphization has been observed in the Cu–Zr system by molecular dynamics simulations using the solid solution and sandwich models. Simulations using the solid solution models not only reproduce the experimentally observed crystal-to-amorphous transition in the system, but also clarify that the physical origin of the transition is the crystalline lattice collapsing while the solute atoms are exceeding the critical solid solubilities, 8 at. % of Cu and 10 at. % of Zr in the hcp Zr-based and fcc Cu-based solid solutions, respectively, which matches well with that observed in experiments. Simulations using the Cu/Zr/Cu sandwich models indicate that the amorphization is initiated by the mutual diffusion of the atoms and that the Cu–Zr amorphous layer grows in a layer-by-layer kinetics featuring a so-called asymmetric-growth behavior. The growth of the amorphous interlayer can be divided into three stages: the fast nucleating stage, the diffusion-growing stage and the steady finishing stage.
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  • Suhas Ganesh Tagare, Yadagiri Rameshwar, Shakira Sultana
    2008 Volume 77 Issue 10 Pages 104401
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Küppers–Lortz instability is considered for rotating thermohaline convection with finite Prandtl number. The threshold Taylor number Tac and critical angle ψc for the onset of Küppers–Lortz instability are studied as a function of the salinity Rayleigh number R2 and Lewis number L (ratio of saline diffusivity κS to thermal diffusivity κT) for stress-free boundary conditions. We determine the effect of the Lewis number and salinity Rayleigh number on the threshold Taylor number and the critical angle for the onset of Küppers–Lortz instability when R2>0 and R2<0, L=0.1 and 0.25, and for finite Prandtl numbers (1.5≤Pr≤150).
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  • Makoto Morinaga
    2008 Volume 77 Issue 10 Pages 104402
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We propose and experimentally demonstrate a novel scheme to magneto-optically trap neutral atoms in a ring shaped trap which could be used for efficient loading of atoms into a circular magnetic trap. Two sets of anti-Helmholz coils having a common center and oriented coaxially are used to generate a circle of zero magnetic field. Six laser beams of proper frequency and polarization then trap atoms onto this circle.
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  • Kanako Sato, Yukito Tanabe, Eiichi Hanamura
    2008 Volume 77 Issue 10 Pages 104403
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The reciprocity theorem is observed to break down in the Raman scattering of Eg-mode phonons in the TiO2 crystal; however, A1g and B1g modes obey the theorem within experimental error. The origin of this violation is theoretically traced to the contribution of the wave-vector-dependent term of the Raman tensor.
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  • Hidenori Hasimoto
    2008 Volume 77 Issue 10 Pages 104601
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    A doubly periodic fundamental solution of a Poisson equation is given in terms of the Weierstrass elliptic function and its difference from the Fourier series solution S1 [H. Hasimoto: J. Fluid Mech. 5 (1959) 317] is given as an explicit constant.
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  • Rikiya Yoshida, Hiroyuki Okazaki, Mitsutoshi Tajima, Takayuki Muro, Iz ...
    2008 Volume 77 Issue 10 Pages 104701
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have performed x-ray photoemission spectroscopy on the system of noncentrosymmetric superconductor, Li2(PdxPt1−x)3B. For Li2Pt3B, we found two major peaks with two other weak components, and the band calculations were in agreement with the observation. The assignment of valence band features using the calculated partial density of states determined that Pt 5d and B 2p contribute to the density of states at the Fermi level. The effect of antisymmetric spin–orbit coupling on the band structure might have been probed, and the analysis on the effect of Pt incorporation into the system indicates the smooth evolution of electronic structures. We presented the measurements of core levels (Pd 3d, Pt 4f, and B 1s) and discussed the chemical bonding states and electronic structures from them.
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  • Takuya Yoshioka, Akihisa Koga, Norio Kawakami
    2008 Volume 77 Issue 10 Pages 104702
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the bandwidth-controlled Mott transition in the Hubbard model on the checkerboard lattice at half filling using the path-integral renormalization group (PIRG) method. It is demonstrated that the system undergoes a first-order phase transition to the plaquette-singlet insulating phase at a finite Hubbard interaction. This conclusion is drawn via a detailed analysis of the spin and charge correlations around the phase transition point by means of the PIRG method aided with a new iteration scheme introduced in this paper.
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  • Yoichi Nishiwaki, Tota Nakamura, Akira Oosawa, Kazuhisa Kakurai, Norik ...
    2008 Volume 77 Issue 10 Pages 104703
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Powder and single-crystal neutron diffraction measurements were performed on RbCoBr3. The magnetic phase transitions of this compound are well explained by the Ising spin model for a distorted triangular lattice. Magnetic peaks of powder diffraction patterns at 34 and 20 K closely fit a partial disordered phase and a ferrimagnetic phase, respectively. The temperature dependences of the (h,h,1) scan profile and magnetic Bragg peak heights at (1,1,1), (1⁄3,1⁄3,1), and (2⁄3,2⁄3,1) were measured for a single-crystal sample. We conclude that the ferrimagnetic phase only exists below 30.5 K. The partial disordered phase is identified between 30.5 (=TN2) and 37.2 K (=TN1). We found a characteristic linear increase in the (1,1,1) peak height below TN2 with decreasing temperature. These results show that a lattice distortion couples to the spin system. Numerical simulations are also performed to estimate magnetic interaction parameters.
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  • Hiroyasu Koizumi
    2008 Volume 77 Issue 10 Pages 104704
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We study spin-wave excitations in an effectively half-filled Hubbard model, where the effectively half-filled situation is realized when all holes doped in the exactly half-filled parent compound become self-trapped lattice polarons, and their hopping rate is much slower than the neutron scattering time of magnetic excitation measurements. It is further assumed that the doped holes become stabilizing centers of spin vortices; thus, the spin texture is not necessarily that of an antiferromagnet. We derive a new spin Hamiltonian that is suitable for this situation by extending the usual antiferromagnetic Heisenberg model. It is shown that two modes of spin-wave excitations exist in this new spin Hamiltonian: the first is the one exhibits antiferromagetic dispersion in high energy excitations; the other shows a sharp commensurate peak at the excitation energy maximum, and a broadened dispersion at energies below. It is shown that the sum of these two modes form an hourglass-shaped magnetic excitation spectrum observed in the underdoped cuprate.
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  • Makoto Yoshida, Nobuyuki Ogata, Masashi Takigawa, Taro Kitano, Hiroshi ...
    2008 Volume 77 Issue 10 Pages 104705
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report nuclear magnetic resonance (NMR) studies in the antiferromagnetic state of the quasi-two-dimensional (CuBr)LaNb2O7. The NMR spectra at zero magnetic field and 4.2 K indicate a unique Cu and Br sites with an internal field of 5.7 T (at Cu) and 16.4 T (at Br), confirming a magnetic order. For the large internal field at the Br sites to be compatible with the collinear antiferromagnetic order observed by neutron diffraction experiments, the Br atoms must move significantly off the center of the square of the Cu sublattice so that the Br nuclei couple predominantly to two parallel Cu moments. While invalidating the frustrated J1J2 model defined on a C4-symmetric square lattice, our results are compatible with the structural model proposed for (CuCl)LaNb2O7 by Yoshida et al.
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  • Shoji Ishibashi, Kiyoyuki Terakura
    2008 Volume 77 Issue 10 Pages 104706
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We perform a systematic study of electronic structures and potential profiles based on the ab initio calculations for LaAlO3/SrTiO3 (001)-stacking thin films [(TiO2–SrO)2(AlO2–LaO)n and (SrO–TiO2)2(LaO–AlO2)n (n=1,2,3,4,5)] with and without atomic position relaxation. To eliminate artifacts from periodic boundary condition, the exact Coulomb cutoff technique [Rozzi et al.: Phys. Rev. B 73 (2006) 205119] is applied. Without atomic position relaxation, the system is a metal for all the 10 cases. In contrast, with atomic position relaxation, systems with n≤3 have finite band gaps though those with n=4,5 are metals. However, careful inspection reveals that, even for n=4 and 5, the n-type interface (LaO–TiO2) is conducting while the p-type interface (SrO–AlO2) is insulating. Screening mechanisms are discussed for cases with and without atomic position relaxation.
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  • Yoshihiro Ishibashi, Makoto Iwata
    2008 Volume 77 Issue 10 Pages 104707
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Lattice vibrations in finite systems with the boundary conditions given as the extrapolation lengths are studied on the basis of the continuum model. The system may be symmetric or asymmetric regarding the extrapolation lengths, which can be positive, negative, or of mixed signs. In general, even cosine modes and odd sine modes appear alternately from the low-frequency side, but the lowest cosine mode changes to the cosh mode and the second-lowest sine mode may change to the sinh mode when the extrapolation lengths at both boundaries are negative. On the other hand, it is not possible to assign the sin (sinh) mode or cos (cosh) mode to the lowest-frequency mode in the case of mixed-sign extrapolation lengths. Orthogonality between the normal modes can be proved using the boundary conditions in spite of the fact that the wavenumbers Ki of the normal modes are mutually incommensurate.
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  • Hiromi Kashiwaya, Tetsuro Matsumoto, Hajime Shibata, Satoshi Kashiwaya ...
    2008 Volume 77 Issue 10 Pages 104708
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The switching dynamics of current-biased Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions (IJJs) was studied to clarify the effects of d-wave superconductivity and the stack structure on switching properties. High-quality IJJs were fabricated, and then the temperature dependence of the switching probability distribution was measured for the first and second switchings. Although the standard deviation of the distribution detected for both switchings showed similar saturation characteristics with decreasing temperature, the temperature at saturation was about thirteenfold higher for the second switching than for the first switching. The properties of the first switching can be explained in terms of a conventional underdamped JJ, that is, macroscopic quantum tunneling below the crossover temperature, and thermal activation with a quality factor of 70±20 above the crossover temperature. In contrast, the relatively higher effective temperature for the second switching evaluated from the switching probability distribution suggests a predominant thermal activation process under the influence of the self-heating effect even at sufficiently low temperatures.
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  • Yoko Miura, Yukio Yasui, Taketo Moyoshi, Masatoshi Sato, Kazuhisa Kaku ...
    2008 Volume 77 Issue 10 Pages 104709
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Magnetic excitation spectra of quantum spins of Na3Cu2SbO6 with a distorted honeycomb structure have been measured by neutron inelastic scattering. The intensity distribution and the dispersion curves of the excitations indicate that the spin system can be well understood by considering one-dimensional spin chains formed of Cu2+ ions on a lattice of alternating the shorter and longer spacings along the b-axis. The exchange interactions between the neighboring spins with the shorter and longer spacings correspond to ferromagnetic and antiferromagnetic interactions, respectively. These findings are consistent with those we reported previously on the basis of macroscopic measurements. The observed gap ΔG is 8.9 meV and the energies of the antiferromagnetic and ferromagnetic interactions have been found to be 13.9 and −12.5 meV, respectively.
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  • Yuji Takeda, Nguyen Duc Dung, Yasunori Nakano, Tatsurou Ishikura, Shug ...
    2008 Volume 77 Issue 10 Pages 104710
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Specific heat measurements on a series of ternary compound RCu2Si2 (R: La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) single crystals have been performed by the quasi-adiabatic heat pulse method in the wide temperature range from 0.1 to 80 K. Almost all the compounds show antiferromagnetic orderings at low temperatures. We found the first-order like very sharp specific heat peaks in RCu2Si2 with R=Gd, Tb, Dy, Ho, and Er. Especially, the antiferromagnetic ordering in DyCu2Si2 is found to be a first-order transition. From the analyses of the temperature dependence of magnetic entropy, we confirmed that the total splitting energy of the crystalline electric field (CEF) scheme of R3+ ion in RCu2Si2 is about 100 K in all the compounds studied here, except for YbCu2Si2. In addition, we observed the nuclear specific heat at low temperatures and estimated the magnitude of internal effective magnetic field Heff at the nucleus.
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  • Hazuki Kawano-Furukawa, Seiko Ohira-Kawamura, Hitomi Tsukagoshi, Chiya ...
    2008 Volume 77 Issue 10 Pages 104711
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Recently Nakai et al. reported a theoretical HT phase diagram of flux line lattice (FLL) structure in which successive transitions from a triangular, a square (\\squarev), a triangular and another square (\\squareg) occur with increasing a magnetic field. Here \\squarev and \\squareg indicate the FLL structures reflecting anisotropies in the Fermi velocity and the superconducting gap, respectively. In the case of YNi2B2C, \\squarev and \\squareg should rotate by 45°. The low field transition from triangular to \\squarev is observed in RENi2B2C (RE=Er, Tm, Lu, and Y). However, there is no experimental evidence for the appearance of \\squareg phase so far. We studied the FLL structure of YNi2B2C in the higher field region by small-angle neutron scattering. Our results show that a large area of the HT phase diagram is occupied by \\squarev phase and there is no evidence for the appearance of \\squareg lattice.
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  • Akitaka Nakanishi, Takahiro Ishikawa, Hitose Nagara, Kouichi Kusakabe
    2008 Volume 77 Issue 10 Pages 104712
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    By means of first-principles calculations, we studied stable lattice structures and estimated superconducting transition temperature of CaSi2 at high pressure. Our simulation shows stability of the AlB2 structure in a pressure range above 17 GPa. In this structure, doubly degenerated optical phonon modes, in which the neighboring silicon atoms oscillate alternately in a silicon plane, show prominently strong interaction with the conduction electrons. In addition there exists a softened optical mode (out-of-plan motion of silicon atoms), whose strength of the electron–phonon interaction is nearly the same as the above mode. The density of states at the Fermi level in the AlB2 structure is higher than that in the trigonal structure. These findings and the estimation of the transition temperature strongly suggest that higher Tc is expected in the AlB2 structure than the trigonal structures which are known so far.
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  • Satoru Ohno, Yojiro Oba, Shin Yabuuchi, Tetsuya Sato, Hiroyuki Kageshi ...
    2008 Volume 77 Issue 10 Pages 104713
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Magnetism of single-walled carbon nanotubes (SWNTs) filled with Pd in pseudo one-dimension is investigated based on the electronic structure obtained using the first-principle calculation. In addition, the stability of Pd nanowire inside SWNT is evaluated through the calculation of binding energy. The Pd monostrand nanowire with the inter-atomic distance of 2.49 Å, which shows ferromagnetism in the free-standing state, has the ferromagnetic moment also in the armchair type SWNTs with the diameter lager than 6.9 Å although the magnetic moment is smaller than that of the corresponding free-standing Pd nanowire. The pseudo one-dimensional fcc Pd nanowire with the cross section of the (111) plane in the (14,0) SWNT has ferromagnetic moment, where the inter-atomic distance is elongated by 28% along the longitudinal axis of SWNT compared with the equilibrium distance, so as to adjust the unit cell size of SWNT. However, the Pd(100) nanowire in (8,8) SWNT does not show ferromagnetism although it has almost the same inter-atomic distance as that of the (111) nanowire in (14,0) SWNT. This can be interpreted by means of the magnetism of planar Pd clusters whose laminating composes the nanowire.
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  • Takayuki Shibata, Fumiya Nakada, Hayato Kamioka, Yutaka Moritomo
    2008 Volume 77 Issue 10 Pages 104714
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    Magnetics and electronic properties has been investigated for the Prussian blue type cyano-bridged transition metal compound, Na0.72−δNi[Fe(CN)6]0.68·5.1H2O (0.0≤δ≤0.58), as a function of the hole concentration δ of the d-electron system. Mother compound (δ=0) takes Ni2+ (t2g6eg2: S=1)–Fe2+ (t2g6: S=0) configuration, and is paramagnetic down to zero temperature. Holes are selectively introduced on the Fe site. Ferromagnetic transition appears at δ=0.26, and the transition temperature TC increases from 11 K at δ=0.26 to 21 K at δ=0.58. We further systematically investigated the absorption spectra in the infrared–violet region against δ. We compared these magnetic and electronic properties of the valence-controlled Ni–Fe compound with those of an isostructural valence-controlled Co–Fe compound.
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  • Ichihiro Yamauchi, Masayuki Itoh, Touru Yamauchi, Yutaka Ueda
    2008 Volume 77 Issue 10 Pages 104715
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The 51V nuclear spin–lattice relaxation rate 1⁄T1 has been measured in various magnetic fields H to study the spin dynamics in the metallic phase of the quasi-one-dimensional conductor β-Na0.33V2O5, which undergoes the metal–insulator transition at TMI∼135 K. We observe an H dependence of 1⁄T1T owing to the spin diffusion that is expected to appear in one-dimensional magnetic systems. The H dependence allows us to separate 1⁄T1T into the q∼0 and q∼2kF contributions. The q∼0 and q∼2kF contributions at the V2 site are suppressed by the Na order–disorder transition at TNa∼242 K, whereas the dominant q∼2kF contributions at the V3 site are not suppressed at TNa. We discuss the spin dynamics based on the Luttinger liquid theory.
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  • Kotaro Iwata, Yoshiyuki Yoshida, Masashi Kosaka, Susumu Katano
    2008 Volume 77 Issue 10 Pages 104716
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have investigated the structural, magnetic, and electronic properties of single-crystalline Sr3−xCaxRu2O7 (0≤x≤3) grown by a floating-zone method. The results of X-ray diffraction, magnetic susceptibility, specific heat, and electrical resistivity measurements reveal that this system shows a novel phase diagram. With increasing Ca content, the enhanced paramagnetism of Sr3Ru2O7 is suppressed, and a phase with a ferromagnetic correlation (0.5\\lesssimx\\lesssim1.2) emerges. This phase adjoins an antiferromagnetic two-dimensional metallic phase (1.2\\lesssimx≤3.0). At the border between these two phases, discontinuous changes in the lattice parameters are observed. In the ferromagnetically correlated phase, the density of states is significantly enhanced. In the antiferromagnetic phase, the magnetic easy axis changes continuously from the c-axis to the ab-plane with increasing Ca content. These magnetic and electronic properties are strongly coupled with structural distortions such as the rotation and tilting of the RuO6 octahedra of this system.
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  • Jae-Yeap Lee, Eun-Mi Choi, Hyun-Sook Lee, Moo-Hyun Cho, Å. A. F. ...
    2008 Volume 77 Issue 10 Pages 104717
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The origin of the magnetic flux noise in MgB2 thin films is believed to be a thermo-magnetic instability, where the local dissipation created by vortex motion leads to reduced pinning, and forms a positive feedback loop which can develop into a thermo-magnetic runaway. However, only the lower threshold field (Hl) for the appearance of this noise was investigated by the magneto-optics (MO) technique due to the field limit of the MO indicator. In this paper, we report the upper threshold field, (Hu) which is successfully obtained by different technique using a vibrating sample magnetometer while varying temperature and the field interval. After the analysis of magnetic hysteresis curves, we found that Hu is strongly depends on sample geometry and temperature. This is consistent with the phenomenological model mentioned above.
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  • Hazuki Kawano-Furukawa, Takashi Nagata, Haruko Takeshita, Mai Matsumot ...
    2008 Volume 77 Issue 10 Pages 104718
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    A stable and microscopic coexistence state between weak ferromagnetism (WFM) and superconductivity (SC) is realized in the type II superconductor ErNi2B2C (Tc=10.5 K) below its WFM transition temperature, TWFM∼2.3 K. An internal magnetic field (Hint) mediated by WFM moments seems to be slightly higher than its lower critical magnetic field (Hc1), and thus a spontaneous vortex phase is expected to be realized. However, since TcTWFM, a pinning effect makes it difficult to verify the spontaneous vortex phase experimentally. To find a system with TcTWFM, we investigated magnetism and superconductivity in Er1−xTbxNi2B2C by magnetization, resistivity and neutron diffraction measurements. In contrast to our expectations, the results show that Tc drops steeply even in a small Tb doping region, where TWFM also decreases due to a magnetic competition in anisotropy, and the relationship Tc>TWFM is always reserved. In the system with x=0.2, an upper critical field (Hc2) shows hysteresis behavior below ∼1 K, which was attributed to the WFM order below it.
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  • Vu Van Hung, Kinichi Masuda-Jindo, Nguyen Thi Hoa
    2008 Volume 77 Issue 10 Pages 104801
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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    The elastic properties of cubic metals have been studied using the analytic free energy formulas derived from the quantum statistical moment method (SMM). The three independent elastic constants C11, C12, and C44 of cubic metals are calculated as a function of the temperature taking into account the anharmonicity of thermal lattice vibrations, and compared with the available experimental results. The particular attention has been paid to the understanding of the anharmonicity effects of thermal lattice vibrations on the elastic properties and thermodynamic crystalline stabilities of the metals in comparison with those by classical treatments of SMM.
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  • Wataru Sato, Yasufumi Komeno, Minoru Tanigaki, Akihiro Taniguchi, Sato ...
    2008 Volume 77 Issue 10 Pages 105001
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Mitsuharu Nagasawa, Tokiko Nagasawa, Koichi Ichimura, Kazushige Nomura
    2008 Volume 77 Issue 10 Pages 105002
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Hirofumi Matsuhata, Chul-Ho Lee, Kunihiro Kihou, Hiroshi Eisaki, Hijir ...
    2008 Volume 77 Issue 10 Pages 105003
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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  • Hideto Fukazawa, Nao Takeshita, Takehiro Yamazaki, Kenji Kondo, Kenji ...
    2008 Volume 77 Issue 10 Pages 105004
    Published: October 15, 2008
    Released on J-STAGE: December 28, 2011
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