Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 77, Issue 11
Displaying 1-50 of 60 articles from this issue
  • Harry Kojima, Hidehiko Ishimoto
    2008 Volume 77 Issue 11 Pages 111001
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Under applied magnetic field, the originally single superfluid 3He transition near 3 mK in zero field splits into two transitions between which a new A1 phase emerges. The two second order transitions are marked by abrupt changes in viscosity, zero sound attenuation and nuclear magnetic resonance. To date, the maximum magnetic field for producing A1 phase is 15 T. The A1 phase has been identified with a spin-polarized (ferromagnetic) superfluid system which breaks the relative symmetry between spin, orbit and gauge spaces. A superfluid mass current in A1 is simultaneously a spin current resulting in the propagation of spin-entropy wave. Experiments with spin-entropy wave provide measurements of anisotropic superfluid density and strong coupling parameters, spin diffusion coefficient and texture transformations. Owing to the spin-polarized nature, superflows may be generated by applied magnetic field gradients and measured from the induced magnetic fountain pressure. The mechanical spin density detector is developed to measure the spin relaxation in A1 phase. The observed unexpected temperature dependence of the spin relaxation time gives evidence that the A1 phase contains a small amount of the predicted minority spin condensate from dipolar interaction energy.
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  • William P. Halperin, Hyoungsoon Choi, John P. Davis, Johannes Pollanen
    2008 Volume 77 Issue 11 Pages 111002
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The discovery of superfluid 3He in high porosity silica aerogels, and subsequent experimental and theoretical work, have led to a better general understanding of quasiparticle scattering from impurities in unconventional pairing systems. It is immensely helpful for understanding impurity effects in the case of superfluid 3He that the structure of its order parameter is well-established. An overview of impurity effects is presented with emphasis on those experiments which have a quantitative interpretation in terms of theoretical models for homogeneous and inhomogeneous scattering. The latter can account successfully for most experimental results.
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  • Katsuhiko Nagai, Yasushi Nagato, Mikio Yamamoto, Seiji Higashitani
    2008 Volume 77 Issue 11 Pages 111003
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We discuss on the surface bound states in superfluid 3He and their observation by transverse acoustic impedance measurement from a theoretical view point. We use a quasi-classical Green’s function theory with random S matrix model for treating rough surface effects. We show that the transverse impedance quite nicely reflects the density of states of the surface bound states.
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  • Kimitoshi Kono, Hiroki Ikegami, Yuriy P. Monarkha
    2008 Volume 77 Issue 11 Pages 111004
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    A quasiparticle scattering model developed by Monarkha and Kono is explored further to include magnetic field effects on superfluid 3He. It successfully explains the absence of magnetic field effects in superfluid 3He-A and normal 3He. Both an explicit magnetic-field-dependent term in the Bogoliubov quasiparticle energy and the distortion of energy gap are the origin of anisotropic properties of superfluid 3He-B in magnetic field. In order to quantitatively compare the model with experimental observation, the energy gap distortion has been numerically evaluated by taking into account Landau’s Fermi liquid effect up to F0a. The Leggett rotation is considered in an ad hoc fashion in 3He-B. The experimental data can be satisfactorily interpreted by assuming that the rotation considered to be realized only in the vicinity of the free surface extends to the bulk. The numerical value of the Landau parameter is important in obtaining quantitative agreement. This might provide a new experimental possibility for determining Landau parameters under zero pressure.
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  • D. Ian Bradley, Shaun N. Fisher, Anthony M. Guénault, Richard P ...
    2008 Volume 77 Issue 11 Pages 111005
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The structure of the order parameter in superfluid 3He mimics closely the analogous structure of the “metric” of the Universe. Since the superfluid may exist in several phases we can, using a magnetic field gradient, set up coherent phase boundaries in the superfluid which are the closest laboratory analogues we have to cosmological branes. We find that if we annihilate two such branes (an AB and a BA interface) then we find that the annihilation leaves relic defects in the superfluid texture. These results can help to “validate” those braneworld scenarios where brane annihilation is thought similarly to lead to the formation of topological defects such as cosmic strings.
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  • Makoto Tsubota
    2008 Volume 77 Issue 11 Pages 111006
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The present article reviews the recent developments in the physics of quantum turbulence. Quantum turbulence (QT) was discovered in superfluid 4He in the 1950s, and the research has tended toward a new direction since the mid 90s. The similarities and differences between quantum and classical turbulence have become an important area of research. QT is comprised of quantized vortices that are definite topological defects, being expected to yield a model of turbulence that is much simpler than the classical model. The general introduction of the issue and a brief review on classical turbulence are followed by a description of the dynamics of quantized vortices. Then, we discuss the energy spectrum of QT at very low temperatures. At low wavenumbers, the energy is transferred through the Richardson cascade of quantized vortices, and the spectrum obeys the Kolmogorov law, which is the most important statistical law in turbulence; this classical region shows the similarity to conventional turbulence. At higher wavenumbers, the energy is transferred by the Kelvin-wave cascade on each vortex. This quantum regime depends strongly on the nature of each quantized vortex. The possible dissipation mechanism is discussed. Finally, important new experimental studies, which include investigations into temperature-dependent transition to QT, dissipation at very low temperatures, QT created by vibrating structures, and visualization of QT, are reviewed. The present article concludes with a brief look at QT in atomic Bose–Einstein condensates.
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  • Matthew S. Paoletti, Ralph B. Fiorito, Katepalli R. Sreenivasan, Danie ...
    2008 Volume 77 Issue 11 Pages 111007
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We discuss an experimental technique to visualize motion in the bulk of superfluid 4He by tracking micron-sized solid hydrogen tracers. The behavior of the tracers is complex since they may be trapped by the quantized vortices while also interacting with the normal fluid via Stokes drag. We discuss the mechanism by which tracers may be trapped by quantized vortices as well as the dependencies on hydrogen volume fraction, temperature, and flow properties. We apply this technique to study the dynamics of a thermal counterflow. Our observations serve as a direct confirmation of the two-fluid model as well as a quantitative test of the normal fluid velocity dependence on the applied heat flux.
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  • Humphrey J. Maris
    2008 Volume 77 Issue 11 Pages 111008
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    An electron injected into liquid helium forces open a small cavity that is free of helium atoms. This object is referred to as an electron bubble, and has been studied experimentally and theoretically for many years. At first sight, it would appear that because helium atoms have such a simple electronic structure and are so chemically inert, it should be very easy to understand the properties of these electron bubbles. However, it turns out that while for some properties theory and experiment are in excellent quantitative agreement, there are other experiments for which there is currently no understanding at all.
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  • Yuichi Okuda, Ryuji Nomura
    2008 Volume 77 Issue 11 Pages 111009
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The new aspects of crystal growth in solid 4He at low temperatures are revealed by manipulating the crystal with a radiation pressure of acoustic waves. The acoustic radiation pressure is generally a tiny nonlinear effect, but it has given unexpected effect on the surface of 4He owing to the markedly high growth rate of the crystal. Radiation pressure induces crystallization or melting. Owing to the strong temperature dependences of the growth rate of an atomically rough surface, which increases divergingly towards T=0, and the numerical value of the ratio of the sound velocities in both phases, the crystal melts at high temperatures when the sound wave is applied from the solid side, while it grows at low temperatures under the same conditions. We found a new type of growth mechanism of a c-facet driven by a strong radiation pressure. The growth rate of a c-facet was found to be much higher than the conventional screw-dislocation-mediated mechanism. Theoretical analysis that treated elementary steps as quantum mechanical quasi-particles reproduced the observed important feasures. The superflow around steps was taken into account as the kinetic energy of the steps. Finally, it was demonstrated that the use of radiation pressure enables the creation of negative crystals or superfluid bubbles in the crystal. Various interesting motions and shapes of the negative crystal were observed and interpreted using a simple model.
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  • Davide Emilio Galli, Luciano Reatto
    2008 Volume 77 Issue 11 Pages 111010
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The possibility of a supersolid state of matter, i.e., a crystalline solid exhibiting superfluid properties, first appeared in theoretical studies about forty years ago. After a long period of little interest due to the lack of experimental evidence, it has attracted strong experimental and theoretical attention in the last few years since Kim and Chan (Penn State, U.S.A.) reported evidence for nonclassical rotational inertia effects, a typical signature of superfluidity, in samples of solid 4He. Since this “first observation”, other experimental groups have observed such effects in the response to the rotation of samples of crystalline helium, and it has become clear that the response of the solid is extremely sensitive to growth conditions, annealing processes, and 3He impurities. A peak in the specific heat in the same range of temperatures has been reported as well as anomalies in the elastic behaviour of solid 4He with a strong resemblance to the phenomena revealed by torsional oscillator experiments. Very recently, the observation of unusual mass transport in hcp solid 4He has also been reported, suggesting superflow. From the theoretical point of view, powerful simulation methods have been used to study solid 4He, but the interpretation of the data is still rather difficult; dealing with the question of supersolidity means that one has to face not only the problem of the coexistence of quantum coherence phenomena and crystalline order, exploring the realm of spontaneous symmetry breaking and quantum field theory, but also the problem of the role of disorder, i.e., how defects, such as vacancies, impurities, dislocations, and grain boundaries, participate in the phase transition mechanism.
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  • Keiya Shirahama, Keiichi Yamamoto, Yoshiyuki Shibayama
    2008 Volume 77 Issue 11 Pages 111011
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    4He confined in nanoporous media is an excellent model boson system in a confinement potential. We have studied the superfluid and thermodynamic properties of 4He confined in a porous glass that has nanopores of 2.5 nm diameter. It is shown that the confinement of 4He in nanopores produces a new quantum state, the localized Bose–Einstein condensation (LBEC) state, and markedly alters the pressure–temperature (PT) phase diagram. In the LBEC state the global phase coherence is destroyed by strong atomic correlation or by the random potential of a substrate. The formation of LBEC leads to an anomalous reduction of the superfluid transition temperature Tc, determined by the torsional oscillator technique, and the behavior of a quantum phase transition near 0 K. The contributions of roton and phonon excitations to the heat capacity provide definitive evidence of the LBEC state.
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  • Nobuo Wada, Milton W. Cole
    2008 Volume 77 Issue 11 Pages 111012
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The 4He and 3He quantum fluids in various dimensions and with interactions different from those of the bulk fluids have been realized under the new extreme conditions constituted in nanopores. The 4He fluid films adsorbed in one-dimensional (1D) nanopores form nano-quantum fluid. The 4He films formed in 1D and 3D nanopores manifest 1D and 3D phonon states, respectively, at sufficiently low temperatures. Their superfluid onsets show an obvious dependence on the pore connectivity. The 2D Kosterlitz–Thouless superfluid transition was studied at extremely high frequencies where the vortex diffusion length in a period is as small as the core diameter. In the 1D and 3D nanopores preplated with 4He films, the 3He gases at dilute densities show dimensional crossovers from the 2D Boltzmann gas to the 1D and 3D gas states, respectively, with decreasing temperature. The degenerate states of 3He in nanopores are expected to depend on the dimensionality and the interactions, which are different from those of the bulk liquids. Zero-dimensional fluids, i.e., quantum clusters, are likely to be realized in nanocages of the Y-type zeolite.
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  • Hiroshi Fukuyama
    2008 Volume 77 Issue 11 Pages 111013
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Recent studies of nuclear magnetism of monolayer helium three (3He) adsorbed on graphite are reviewed. This system provides us a fascinating testing ground for physics of highly frustrated quantum spins of two dimensions (2D) such as spin liquids. Particular emphasis is devoted to the gapless spin liquid state observed in the low-density commensurate phase (4/7 phase) in the second layer. Existing experiments on heat capacity in zero magnetic field and magnetization in low fields of this phase show unambiguously the gapless excitations down to three orders of magnitude lower temperatures than the relevant exchange interactions (≈1 mK). This is a new class of spin liquid, and recently electronic counterparts are found in quasi-1D and -2D conductors. On the other hand, measured magnetic properties of the incommensurate phase at much higher densities can be described as a nearly ideal 2D S=1⁄2 ferromagnet on a triangular lattice. We propose the existence of a new ferromagnetic commensurate phase at a density in between the 4/7 and incommensurate phases based on new heat capacity data. None of these phases show signatures of finite temperature phase transitions being consistent with the Mermin–Wagner theorem. The exchange interactions among 3He nuclear spins originate from atom-atom tunnel exchanges due to the large zero-point motions. Because of the steric hindrance, higher order exchanges like three-, four-, five-, and six-spin ring exchanges are expected to compete each other in similar strengths (MSE model). The applicability of the MSE model to the experimental magnetic properties of this system including its density variation is discussed. It is satisfactory except the fact that the model does not reproduce the gapless nature of the 4/7 phase, which recently stimulates different theoretical approaches such as the Hubbard model.
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  • Yukio Saito, Hiroyuki Hyuga
    2008 Volume 77 Issue 11 Pages 113001
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    To study the establishment of homochirality observed in the crystal growth experiment of chiral molecules from a solution under grinding, we extend the lattice gas model of crystal growth as follows. A lattice site can be occupied by a chiral molecule in R or S form, or can be empty. Molecules form homoclusters by nearest neighbor bonds. They change their chirality if they are isolated monomers in the solution. Grinding is incorporated by cutting and shuffling the system randomly. It is shown that Ostwald ripening without grinding is extremely slow to select chirality, if possible. Grinding alone also cannot achieve chirality selection. For the accomplishment of homochirality, we need an enhanced chirality change on crystalline surface. With this “autocatalytic effect” and the recycling of monomers due to grinding, an exponential increase of crystal enantiomeric excess to homochiral state is realized.
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  • Hidenori Suzuki, Ken’ichi Takano
    2008 Volume 77 Issue 11 Pages 113701
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the J1J2 spin chain consisting of spins with magnitude 1/2. The nearest-neighbor and next-nearest-neighbor exchange interactions are ferromagnetic and antiferromagnetic, respectively, and induce strong frustration. Both these interactions involve the bond alternation. We find exact solutions for all the degenerate ground states at the phase boundary of the ferromagnetic phase. The degeneracy remains irrespective of the two parameters representing the bond alternation. The exact solutions are of recursion formulae in general and of closed forms for no bond alternation in the nearest-neighbor interaction. The exact solutions are applicable to the Δ chain as a special case.
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  • Yuichi Shimakawa, Hiroshi Shiraki, Takashi Saito
    2008 Volume 77 Issue 11 Pages 113702
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Very unusual transitions from ferromagnetic CaCu3Ge4O12 to antiferromagnetic CaCu3Ti4O12 to ferromagnetic CaCu3Sn4O12 are observed in solid solutions of the A-site ordered perovskites. The effective magnetic interaction between Cu2+ spins changes gradually and systematically from ferromagnetic to antiferromagnetic to ferromagnetic in the solid solution. At intermediate compositions the perfect balance of the competing interactions causes unusual instability. The ferromagnetic-to-antiferromagnetic switching is different from the known change by the bond angles mechanism of the superexchange interaction and has not been observed previously in any ferromagnetic-antiferromagnetic compounds. The present solid solutions provide a unique system where either ferromagnetism or antiferromagnetim arises within the simple A-site cubic S=1⁄2 spin sublattice.
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  • Hisashi Kotegawa, Satoru Masaki, Yoshiki Awai, Hideki Tou, Yoshikazu M ...
    2008 Volume 77 Issue 11 Pages 113703
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report the results of 77Se-nuclear magnetic resonance (NMR) in α-FeSe, which exhibits a similar crystal structure to the LaFeAsO1−xFx superconductor and shows superconductivity at 8 K. The nuclear-spin lattice relaxation rate 1⁄T1 shows T3 behavior below the superconducting transition temperature Tc without a coherence peak. The T1T=const. behavior, indicative of the Fermi liquid state, can be seen in a wide temperature range above Tc. The superconductivity in α-FeSe is also an unconventional one as well as LaFeAsO1−xFx and related materials. The FeAs layer is not essential for the occurrence of the unconventional superconductivity.
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  • Takafumi Mizuno, Takuya Iizuka, Shin-ichi Kimura, Kazuyuki Matsubayash ...
    2008 Volume 77 Issue 11 Pages 113704
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report the pressure-dependent optical reflectivity spectra of a strongly correlated insulator, samarium monosulfide (SmS), in the far- and middle-infrared regions to investigate the origin of the pressure-induced phase transition from the black phase to the golden phase. The energy gap becomes narrow with increasing pressure in the black phase. A valence transition from Sm2+ in the black phase to mainly Sm3+ in the golden phase accompanied by spectral change from insulator to metal were observed at the transition pressure of 0.65 GPa. The black-to-golden phase transition occurs when the energy gap size of black SmS becomes the same as the binding energy of the exciton at the indirect energy gap before the gap closes. This result indicates that the valence transition originates from an excitonic instability.
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  • Yuichi Otsuka, Hitoshi Seo, Yukitoshi Motome, Takeo Kato
    2008 Volume 77 Issue 11 Pages 113705
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Finite-temperature phase transitions in quasi-one-dimensional quarter-filled systems are investigated using the extended Hubbard model with electron–lattice coupling. By a quantum Monte Carlo method combined with interchain mean-field approximation, we clarify competing and coexisting behaviors among charge ordering, dimer Mott, and spin-Peierls states. It is pointed out that an anharmonicity of lattice distortions plays an important role in multicritical behaviors. The results are compared with experimental data for quasi-one-dimensional molecular conductors such as DCNQI and TMTTF compounds.
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  • Tetsuya Takimoto
    2008 Volume 77 Issue 11 Pages 113706
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We examine static spin susceptibilities χαβ(q) of spin components Sα and Sβ in the non-centrosymmetric tetragonal system. The anomalous susceptibility, which vanish in centrosymmetric systems, remains showing a momentum dependence like χxx(q)−χyy(q)∼qx2qy2 and χxy(q)+χyx(q)∼qxqy. A characteristic property of the non-centrosymmetric system is the non-vanishing anomalous susceptibility, whose momentum dependence is not invariant to some symmetry operations of the system. As the direct probe of the anomalous spin susceptibility, we propose a polarized neutron scattering experiment, especially, around an ordering wave vector.
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  • Satoru Masubuchi, Ken-ichi Suga, Masashi Ono, Koichi Kindo, Shojiro Ta ...
    2008 Volume 77 Issue 11 Pages 113707
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report on the magnetotransport measurement on a single-layer graphene in pulsed magnetic fields up to B=53 T. With either electron- or hole-type charge carriers, the Hall resistance RH is quantized into RH=(he2−1 with ν=±2, ±6, and ±10, which demonstrates the observation of a half-integer quantum Hall effect (QHE). At B=50 T, the half-integer QHE is even observed at room temperature in spite of a conventional carrier mobility μ=4000 cm2 V−1 s−1.
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  • Katsunori Wakabayashi, Manfred Sigrist
    2008 Volume 77 Issue 11 Pages 113708
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The electronic transport properties in graphene quantum point contacts are numerically studied. The constriction of the quantum point contact induces the zero-conductance Fano resonances in the low-energy single channel transport region near the Dirac point, i.e., perfect reflection. Randomly distributed impurities which alter the resonance energies cause large conductance fluctuation comparable to the ensemble averaged dimensionless conductance. Our results identify a further intriguing effect of impurity scattering in the electronic transport properites of graphene.
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  • Satoru Matsuishi, Yasunori Inoue, Takatoshi Nomura, Masahiro Hirano, H ...
    2008 Volume 77 Issue 11 Pages 113709
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have synthesized a quaternary fluoroarsenide SrFeAsF with the ZrCuSiAs-type structure (P4⁄nmm, a=0.3999 and c=0.8973 nm), which is composed of an alternately stacked (FeAs)δ− and (SrF)δ+ layers, analogous to the FeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction with the anomaly at ∼180 K. The partial replacement of the Fe with Co suppresses the anomaly and induces the superconductivity, while the maximal Tc (4 K for SrFe0.875Co0.125AsF) is much lower than that of the Co-substituted LaFeAsO. Replacement of (LaO)δ+ layers with (SrF)δ+ layers results in a enlargement of the c-axis length (+2.6%). These results suggest the importance of interlayer interaction as a critical Tc-controlling factor in FeAs-based superconductors.
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  • Yuko Senga, Hiroshi Kontani
    2008 Volume 77 Issue 11 Pages 113710
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    To understand the impurity effect on Tc in FeAs superconductors, we analyze a simple two-band BCS model with a repulsive interband interaction. The realized fully gapped superconducting state with sign reversal, which is predicted by spin fluctuation theories in this compound, is suppressed by impurities due to the interband hopping of Cooper pairs, if the interband impurity scattering I′ is equal to the intraband one I. When |I′⁄I|<1, in high contrast, Tc is almost unchanged by strong impurity scattering since interband scattering is almost prohibited by the multiple scattering effect. Since |I′⁄I|∼0.5 is expected, the robustness of superconductivity against impurities in FeAs superconductors is naturally understood in terms of the sign-reversing fully gapped state.
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  • Hitoshi Sugawara, Rikio Settai, Yusuke Doi, Hiroshi Muranaka, Keisuke ...
    2008 Volume 77 Issue 11 Pages 113711
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have succeeded in observing the de Haas–van Alphen (dHvA) effect in LaFePO, the first reported iron-based superconductor in the iron–oxypnictide family. The four detected dHvA frequencies, which correspond to the cross-sectional areas of Fermi surfaces, approximately follow the 1⁄cosθ dependence, where θ is the field-tilted angle from the [001] direction to the [100] and [110] directions in the tetragonal structure. This indicates that all the Fermi surfaces are nearly cylindrical, with the two-dimensional electronic state. The cyclotron effective mass, which was determined from the temperature dependence of the dHvA amplitude, is relatively large, ranging from 1.82 to 2.34m0. The result of energy band structure calculation revealed that the conduction bands mainly consist of 3d electrons of Fe atoms.
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  • Hironari Okada, Kazumi Igawa, Hiroki Takahashi, Yoichi Kamihara, Masah ...
    2008 Volume 77 Issue 11 Pages 113712
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Electrical resistivity measurements under high pressures up to 29 GPa were performed for oxypnictide compound LaFeAsO. We found a pressure-induced superconductivity in LaFeAsO. The maximum value of Tc is 21 K at ∼12 GPa. The pressure dependence of the Tc is similar to those of LaFeAsO1−xFx series reported previously.
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  • Ganapathy Baskaran
    2008 Volume 77 Issue 11 Pages 113713
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We suggest that LaFeAsO is basically a spin-1 Mott insulator that has become an antiferromagnetically ordered bad metal with reduced sublattice moment, by a self (under) doping of an equal and small density (y<<1) of electron and hole carriers. External doping in LaFeAsO1−xFx kills long range antiferromagnetic order and stabilises a liquid of quantum singlet strings (spin-1 Haldane chain). We view this state as two spin-1/2 resonating valence bond (RVB) system, coupled by a weak Hund coupling and bond charge repulsions, leading to an AKLT (Affleck, Kennedy, Lieb, and Tasaki) type spin pairing. A pair of doped holes (electrons) creates an open string and remain at the ends as holon (doublon). Charge ± 2e singlet strings condense to produce high Tc superconductivity. Higher Tc’s are likely in our Mott insulator based scenario, when competing orders are taken care of. As Fe–Fe distance increases from LaFePO to LaFeAsO, we suggest that REFeSb) and REFeBiO (RE: rare earth) and also the chalogenide α-FeTe, if synthesized might be spin-1 Mott insulators, with a prospect for higher superconducting Tc.
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  • Hirotaka Uemura, Hiroyuki Matsuzaki, Yukihiro Takahashi, Tatsuo Hasega ...
    2008 Volume 77 Issue 11 Pages 113714
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Ultrafast charge dynamics in one-dimensional Mott insulators was investigated by femtosecond reflection spectroscopy on three organic molecular compounds, K–tetracyanoquinodimethane (TCNQ), Rb–TCNQ, and bis(ethylenedithio)tetrathiafulvalene (ET)–difluorotetracyanoquinodimethane (F2TCNQ) with different magnitudes of electron–lattice (e–l) interaction. In K– and Rb–TCNQ, photocarriers are localized as polarons with ∼70 fs and recombine with a few ps. In ET–F2TCNQ, photocarriers lead to a metallic state and decay with ∼200 fs. Such differences of the charge dynamics are reasonably interpreted by taking into account the magnitudes of the e–l interactions.
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  • Masa-aki Taniguchi, Masako Bando, Akihiro Nakayama
    2008 Volume 77 Issue 11 Pages 114001
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We propose a dynamical model for business cycle based on an optimal diffusion index (DI) model. In the model there exists a conserved quantity, which corresponds to the total energy in a dynamical system. We found that the business cycle with the period 5–8 years is favorably reproduced, since the model predicts a periodic motion in the conservative system.
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  • Hiroshi Ueda, Tomotoshi Nishino, Koichi Kusakabe
    2008 Volume 77 Issue 11 Pages 114002
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report a means of wave function estimation for the density matrix renormalization group (DMRG) method applied to quantum systems, which has two-site modulation, when the system size extension is necessary in both the finite and infinite algorithms. The estimation is performed by renormalization group (RG) transformation applied to the ground-state wave function, which is represented by a matrix product. This RG scheme is known as the product wave function renormalization group (PWFRG) method. In order to treat two-site modulation, the operation of the RG transformation is shifted by two lattice sites. It turns out that this two-site shift algorithm enables better wave function estimation in the thermodynamic limit, than the previously known PWFRG algorithm.
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  • Jun Yu, Zhi-kun Xie, Li-xian Yu
    2008 Volume 77 Issue 11 Pages 114003
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The dynamical behavior of the extended Duffing–Van der Pol oscillator is investigated numerically in some detail. Different routes to chaos such as period-doubling bifurcation and intermittency, as well as various shapes of strange attractors and rich dynamical phenomena: crisis, transient chaos, are all observed by using bifurcation diagrams, phase projections and Poincaré maps. To characterize chaotic behavior of this oscillator system, the spectrum of Lyapunov exponent and Lyapunov dimension of the strange attractor are also employed.
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  • Kouichi Okunishi
    2008 Volume 77 Issue 11 Pages 114004
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We calculate the vector spin chirality for S=1⁄2 zigzag spin chains having U(1) symmetry, using the density matrix renormalization group combined with unitary transformation. We then demonstrate the occurrence of the chiral order for the zigzag XY chain and discuss the associated phase transition. The results are consistent with the analysis based on the bosonization and the long distance behaviour of the chirality correlation function. For the S=1⁄2 zigzag Heisenberg chain in a magnetic field, we also verify the chiral order that is predicted by the effective field theory and the chirality correlation function, and then determine its magnetic phase diagram.
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  • Atsuko Odahara, Yasuyuki Gono, Tomonori Fukuchi, Yasuo Wakabayashi, Hi ...
    2008 Volume 77 Issue 11 Pages 114201
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Decays of high-spin isomers (HSIs) with Iπ=49⁄2+ in 143Nd and 147Gd are studied in terms of shape isomerism. Observed large hindrance factors of the electric dipole (E1) transition deexciting HSI in 143Nd and the electric quadrupole (E2) transition deexciting HSI in 147Gd are analyzed by using configurations and deformations obtained by deformed independent particle model calculations. It is pointed out that the strongly hindered decays of HSIs indicate a clear manifestation of the shape differences between HSIs and feeding states by their decays.
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  • Ikuo Fukuda, Yasushige Yonezawa, Haruki Nakamura
    2008 Volume 77 Issue 11 Pages 114301
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We investigate the charge-neutralized summation method proposed by Wolf et al. for evaluating in a very simple manner the electrostatic interaction of a point particle system. We argue conceptional and problematic aspects encountered in the application of this method to molecular dynamics calculation. A novel molecular-dynamics formulation for this method is then proposed and we describe how it resolves formal and practical difficulties in previous approaches. Theoretically consistent force, pairwise potential, and the total energy including a suitable energy correction accompanied by a potential-function deformation are given. To clarify the new concept, the relationship between the charge neutrality and the mirror-image charge expression is discussed.
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  • Masaki Shimizu, Shigeo Kida
    2008 Volume 77 Issue 11 Pages 114401
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The flow in a circular pipe of radius a driven by a constant and uniform axial force is investigated over a range of Reynolds numbers, including the critical value for laminar–turbulent transition. The Navier–Stokes equation for an incompressible viscous fluid is solved numerically by a spectral method as the initial value problem with the no-slip boundary condition on the pipe wall and periodic boundary conditions with period 16πa in the axial direction. The initial condition is given by the Hagen–Poiseuille flow (corresponding to the external force) superimposed with perturbations of finite amplitude. The long-term behaviour of the flow is qualitatively different depending on the Reynolds number Re=Ua⁄ν, where U is the centerline velocity of the above Hagen–Poiseuille flow and ν is the kinematic viscosity of the fluid. For intermediate Reynolds numbers (3300≤Re≤4000) we find a locally turbulent region, called a “puff”, which is advected downstream with velocity close to the mean axial velocity. The velocity fluctuations in the puff change quasi-periodically in time. The upstream boundary, called the “trailing edge” of the puff, sharply divides the laminar and turbulent regions. The mean shape of the trailing edge is determined by the least-squares method using the cross-axial velocity fluctuations in the puff. This will be useful as a reference when the flow structure and/or generation mechanism of a turbulent puff are analysed.
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  • Yoshihiko Nagashima, Sanae-I. Itoh, Shunjiro Shinohara, Masayuki Fukao ...
    2008 Volume 77 Issue 11 Pages 114501
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Spatiotemporal structures of fluctuations with frequencies lower than the ion cyclotron frequency in a cylindrical magnetized plasma are investigated. Drift-wave and low-frequency zonal flow coexist. Electrostatic potentials of the zonal flow and the drift-wave are distributed widely in radius. The radial wave number profile of the zonal flow has a shear structure at the radial location where the drift-wave has a maximal normalized fluctuation amplitude. On the other hand, the radial wave number profile of the drift-wave shows vortex tilting, resulting in the generation of stationary turbulence Reynolds stress gradient per mass density. The envelope and bispectral analyses indicate significant nonlinear interactions between the zonal flow and the drift-wave.
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  • Takashi Sakuma, Xianglian, Norifumi Shimizu, Khairul Basar, Haruyuki ...
    2008 Volume 77 Issue 11 Pages 114601
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The crystal structure of γ-Ag3SBr0.6I0.4 is investigated by X-ray diffraction at 16 K. The low-temperature γ-phase of Ag3SBr0.6I0.4 belongs to an orthorhombic system with the space group C2v7-Pnm21. From the results of Rietveld analysis, it is found that the γ-phase includes an ordered arrangement of Ag atoms. Silver atoms around S atoms construct a distorted octahedron in the crystal. The tetrahedron constructed by anions around Ag atoms is highly distorted.
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  • Atsushi Ito, Hiroaki Nakamura, Arimichi Takayama
    2008 Volume 77 Issue 11 Pages 114602
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report the chemical interaction between a single hydrogen atom and graphene via a classical molecular dynamics simulation using a modified Brenner empirical bond order potential. Three interactions, that is, adsorption, reflection, and penetration, are observed in our simulation. The rates of the interactions depend on the incident energy of the hydrogen atom and the graphene temperature. This dependence can be explained by the following mechanisms: (1) The hydrogen atom experiences a repulsive force due to π electrons. (2) The graphene adsorbs the hydrogen atom and transforms its structure to an “overhang” configuration such as the sp3 state. (3) The expansion of the six-membered ring causes the loss of the kinetic energy of the hydrogen atom during penetration.
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  • Keiichiro Inaura, Youhei Fujitani
    2008 Volume 77 Issue 11 Pages 114603
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We calculate the relaxation rate of the critical concentration fluctuation in a two-component fluid membrane by considering hydrodynamics of the surrounding fluids. Results are compared with the previous results obtained by Seki, Komura, and Imai (2007), who treated the momentum flux from the membrane to its environments using the friction coefficient.
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  • Daisuke Tahara, Masatoshi Imada
    2008 Volume 77 Issue 11 Pages 114701
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Variational wave functions used in the variational Monte Carlo (VMC) method are extensively improved to overcome the biases coming from the assumed variational form of the wave functions. We construct a highly generalized variational form by introducing a large number of variational parameters to the Gutzwiller–Jastrow factor as well as to the one-body part. Moreover, the projection operator to restore the symmetry of the wave function is introduced. These improvements enable to treat fluctuations with long-ranged as well as short-ranged correlations. A highly generalized wave function is implemented by the Pfaffians introduced by Bouchaud et al., together with the stochastic reconfiguration method introduced by Sorella for the parameter optimization. Our framework offers much higher accuracy for strongly correlated electron systems than the conventional variational Monte Carlo methods.
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  • Yoshiro Kakehashi, Takafumi Shimabukuro, Chitoshi Yasuda
    2008 Volume 77 Issue 11 Pages 114702
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    A new wavefunction which improves the Gutzwiller-type local ansatz method has been proposed to describe the correlated electron system. The ground-state energy, double occupation number, momentum distribution function, and quasiparticle weight have been calculated for the half-filled band Hubbard model in infinite dimensions. It is shown that the new wavefunction improves the local-ansatz approach (LA) proposed by Stollhoff and Fulde. Especially, calculated momentum distribution functions show a reasonable momentum dependence. The result qualitatively differs from those obtained by the LA and the Gutzwiller wavefunction. Furthermore, the present approach combined with the projection operator method CPA is shown to describe quantitatively the excitation spectra in the insulator regime as well as the critical Coulomb interactions for a gap formation in infinite dimensions.
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  • Kenji Ohoyama, Kentaro Indoh, Hiroki Yamauchi, Aya Tobo, Eiichi Matsuo ...
    2008 Volume 77 Issue 11 Pages 114703
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Neutron scattering experiments were performed on the single-crystalline DyB2C2 under magnetic fields in order to elucidate the magnetic structures of field-induced phases. The measurements in the a*c* reciprocal lattice plane under the magnetic fields along the [010] direction resulted in finding a new magnetic reflection of 1 0 3⁄4 in a field-induced phase (phase II′′) in addition to the magnetic reflections that are common to those in the phase under a zero magnetic field (phase III). The magnetic unit cell in phase II′′ has dimensions of a×a×4c, where all the Dy magnetic moments on the AFQ structure have advantageous directions to the magnetic field, and their AFQ couplings with the neighbouring moments along the c-axis are partly broken. This magnetic structure model for phase II′′ well explains the magnetisation process at 5 K up to 14 T.
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  • Georg Knebel, Dai Aoki, Jean-Pascal Brison, Jacques Flouquet
    2008 Volume 77 Issue 11 Pages 114704
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The pressure–temperature phase diagram of CeRhIn5 has been studied under high magnetic field by resistivity measurements. Clear signatures of a quantum critical point has been found at a critical pressure of pc≈2.5 GPa. The field induced magnetic state in the superconducting state is stable up to the highest measured field. At pc the antiferromagnetic ground-state under high magnetic field collapses very rapidly. Clear signatures of pc are the strong enhancement of the resistivity in the normal state and of the inelastic scattering term. No clear T2 temperature dependence could be found for pressures above Tc. From the analysis of the upper critical field within a strong coupling model we present the pressure dependence of the coupling parameter λ and the gyromagnetic ratio g. No signatures of a spatially modulated order parameter could be evidenced. A detailed comparison with the magnetic field–temperature phase diagram of CeCoIn5 is given. The comparison between CeRhIn5 and CeCoIn5 points out the importance to take into account the field dependence of the effective mass in the calculation of the superconducting upper critical field Hc2. It suggests also that when the magnetic critical field HM(0) becomes lower than Hc2(0), the persistence of a superconducting pseudo-gap may stick the antiferromagnetism to Hc2(0).
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  • Daisuke Kikuchi, Hitoshi Sugawara, Kenya Tanaka, Hidekazu Aoki, Miki K ...
    2008 Volume 77 Issue 11 Pages 114705
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The electronic properties in SmFe4P12 have been investigated by means of the de Haas–van Alphen effect, transverse magnetoresistance, Hall effect, and band structure calculation. We have found a markedly large anisotropy in the cyclotron effective mass of the 47th band Fermi surface despite its nearly spherical shape. Moreover, this mass enhancement in SmFe4P12 is robust against magnetic field. The transverse magnetoresistance increases nearly quadratically with magnetic field for all field directions; this is unexpected for an ordinary uncompensated metal. The Hall coefficient is found to be 4-fold enhanced at low temperature compared with that at room temperature. These anomalies in transport properties are ascribed to the stronger enhancement of the cyclotron effective mass of the 48th band Fermi surface.
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  • Eiichi Matsuoka, Daichi Usui, Yuta Sasaki, Hironori Nakao, Hiroshi Shi ...
    2008 Volume 77 Issue 11 Pages 114706
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Neutron powder diffraction experiments have been performed on CePd3S4 as well as measurements of magnetic and transport properties on a single-crystalline sample. Magnetic susceptibility increases markedly below TC=6.3 K and a spontaneous magnetization appears below TC. The logarithmic temperature dependence of electrical resistivity implies that CePd3S4 is classified into a Kondo-lattice compound whose Kondo temperature is comparable to TC. Magnetic susceptibility is analyzed satisfactorily with a crystalline electric field model that the 4f ground state of Ce3+ is the Γ8 quartet with the excited Γ7 doublet located at 630 K. The magnetic structure of CePd3S4 was determined to be a canted structure with a canting angle of 51°. Such a canted structure is a result of the ferromagnetic (FM) ordering and simultaneous [100]-type antiferroquadrupolar (AFQ) ordering at TC. The smaller magnetization values and an unexpectedly high TC can be explained by the simultaneous occurrence of AFQ and FM order.
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  • Koichi Ichimura, Makoto Takami, Kazushige Nomura
    2008 Volume 77 Issue 11 Pages 114707
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    Conducting and lateral surfaces of two-dimensional organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br were studied by electron tunneling using scanning tunneling microscopy. The V-shape tunneling conductance curve was observed at the conducting plane in the superconducting phase, attributed to the d-wave pairing symmetry. Tunneling spectra were successfully obtained at various lateral surfaces of crystals. The tunneling conductance curve varies systematically depending on tunneling direction. The conductance curve and its directional dependence are explained by the d-wave with nodes along the direction near π⁄4 from the ka- and kc-axes. The pairing symmetry is of the dx2y2-wave. (If we take the same convention for the magnetic Brillouin zone as high-Tc cuprates with the dx2y2-symmetry, the pairing symmetry of κ-(BEDT-TTF)2Cu[N(CN)2]Br is the dxy-symmetry.) This is the same symmetry as that in the superconducting gap of κ-(BEDT-TTF)2Cu(NCS)2. The zero bias conductance peak (ZBCP) was observed at the tunneling along near π⁄4 from the a- and c-axes. This ZBCP result reinforces the conclusion of the dx2y2-wave symmetry.
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  • Takao Morinari
    2008 Volume 77 Issue 11 Pages 114708
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The effect of fluctuations about the π-flux mean field state for the undoped high-temperature superconductors is investigated. It is shown that fluctuations of the mean fields lead to a self-energy correction that doubles the band width of the fermion dispersion in the lowest order. The dynamical mass generation is associated with the self-energy effect due to the interaction mediated by the Lagrange multiplier field, which is introduced to impose the constraint on the fermions. A self-consistent picture about the mass generation and the propagation of the Lagrange multiplier field without damping is proposed. The antiferromagnetic long-range ordering is described without introducing an additional repulsive interaction. The theory suggests a natural framework to study spin disordered systems in which fermionic excitations are low-lying excitations.
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  • Kentaro Kitagawa, Naoyuki Katayama, Kenya Ohgushi, Makoto Yoshida, Mas ...
    2008 Volume 77 Issue 11 Pages 114709
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We report results of 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown single crystal of BaFe2As2. A first-order antiferromagnetic (AF) transition near 135 K was detected by the splitting of NMR lines, which is accompanied by simultaneous structural transition as evidenced by a sudden large change of the electric field gradient tensor at the As site. The NMR results lead almost uniquely to the stripe spin structure in the AF phase. The data of spin–lattice relaxation rate indicate development of anisotropic spin fluctuations of the stripe-type with decreasing temperature in the paramagnetic phase.
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  • Yasuhiro Saiga, Takashi Sugibayashi, Dai S. Hirashima
    2008 Volume 77 Issue 11 Pages 114710
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    The dynamical mean field theory combined with exact diagonalization is used to study the valence instability in an extended periodic Anderson model. It is found that at fixed total electron number, the f-electron number is rapidly decreased against the f-electron level εf(0) in the presence of the repulsive interaction Ucf between a conduction electron and an f electron. This implies the enhancement of valence fluctuations due to Ucf. In addition, a first-order valence transition is likely to occur, provided the cf mixing is small and Ucf is large enough to be comparable to the band width of conduction electrons. The quantum critical point of valence transition is identified in the εf(0)Ucf plane. Implications for the valence fluctuations of the related Ce compounds are also discussed.
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  • Hironari Okada, Keiichi Koyama, Masashi Nakatake, Kenya Shimada, Hirof ...
    2008 Volume 77 Issue 11 Pages 114711
    Published: November 15, 2008
    Released on J-STAGE: December 28, 2011
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    We have performed photoemission spectroscopy studies of single-crystalline CuV2S4 using synchrotron radiation, in order to clarify the electronic structure changes across the charge density wave (CDW) transitions in a spinel type compound. Photo-energy-dependent studies show a peak structure just below the Fermi level (EF), which undergoes resonant enhancement at an excitation energy hν=54.5 eV. This energy corresponds to the V 3p–3d threshold energy, thus suggesting that the density of states (DOS) at EF is mainly composed of V 3d states. From temperature-dependent measurements, we observe a reduction in spectral DOS at and near EF, leading to the formation of a pseudogap across CDW transition temperatures. The pseudogap energy scale of ∼0.05 eV, identified at the top of the valence band, is significantly larger than the value expected from a BCS-like transition.
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