Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 76, Issue 3
Displaying 1-42 of 42 articles from this issue
  • Jong-Hoon Huh
    2007 Volume 76 Issue 3 Pages 033001
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We report on noise-induced patterns and threshold characteristics for the ac-driven electrohydrodynamic system in nematic liquid crystals. The wave number-dependence of the threshold for the stochastic system was experimentally investigated with controlling intensity rate of noise. The results are discussed in comparison with the previous experimental and theoretical ones. Moreover, unexpected patterns as well as pre-transitional ones are presented.
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  • Katsuya Honda, Fumiki Agata
    2007 Volume 76 Issue 3 Pages 033002
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We consider two types of van der Pol equations with a delay time r to study the Hopf bifurcation due to delay. It is pointed out analytically that, even in the case that a parameter is chosen so as the rest state is stable if r=0, the state becomes unstable when r>rc with a threshold rc. Beyond rc in one type of van der Pol equation, a limit cycle occurs, but it does not appear in the other type.
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  • Akihide Fujisawa, Akihiro Shimizu, Haruhisa Nakano, Shinsuke Ohshima, ...
    2007 Volume 76 Issue 3 Pages 033501
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Electric field fluctuations are directly measured using twin heavy-ion-beam probes in Compact Helical System. The spectrum of the electric field fluctuation reveals the existence of a zonal flow at a frequency of less than 1 kHz, coherent modes with a long correlation length (conjectured as geodesic acoustic modes), and background turbulence. Analyses using a wavelet elucidate nonlinear interactions between these fluctuation components in disparate scales. The highlighted findings are that the turbulent fluctuations should be modulated in response to the direction of zonal flow, and should be suppressed, on average, by the zonal flow. This is the first observation that demonstrates the causal linkage between zonal flow and turbulence in toroidal plasmas at a high temperature.
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  • Yoshitaka Naitoh, Kohji Momotani, Hikaru Nomura, Yan Jun Li, Masami Ka ...
    2007 Volume 76 Issue 3 Pages 033601
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We investigated NC-AFM imaging mechanism on a Si(111)7×7 surface under the strong interaction condition working between dangling bonds on the tip and the surface atoms. The surface adatom appeared in the image as a bright spot, which became larger with stronger interaction condition. Upon further strong interaction, we could detect the rest atoms in the unfaulted half unit of the 7×7 surface image as prominent sharp bright dots with 1 Å width. Besides, the dot appeared with the lateral shift by 2 Å as compared to the surface adatom image. We found the strong covalent interaction between the dangling bonds on the tip atom and the surface atoms influenced onto the image variation.
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  • Kazuyuki Matsubayashi, Keiichiro Imura, Hiroyuki S. Suzuki, Genfu Chen ...
    2007 Volume 76 Issue 3 Pages 033602
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We measured the thermal expansion and heat capacity of the mixed-valence compound SmS that shows an insulator to metal phase transition under pressure. We report a convincing evidence for the existence of not only an electronic specific heat coefficient γ but also a Schottky like gap Δ in the “metal” phase, generally referred to as golden phase. As the pressure increases, γ steeply increases while Δ monotonically decreases. Nevertheless, the product γΔ⁄N is kept constant, where N denotes the number of Sm3+ ion. We argue that a novel bound state is formed in golden phase.
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  • Syuma Yasuzuka, Keizo Murata, Taro Arimoto, Reizo Kato
    2007 Volume 76 Issue 3 Pages 033701
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We have measured the resistivity of the organic conductor TTF-TCNQ under high pressure up to 8.0 GPa using a cubic anvil apparatus. Below 3 GPa, the pressure dependence of the charge-density-wave (CDW) transition temperature, TCDW, is consistent with previous results, except for the observation of the “49 K-transition” at around 1 GPa. Above 3 GPa, TCDW decreases with increasing pressure but the CDW state survives even at 8.0 GPa. At 8.0 GPa, however, the resistivity shows metallic behavior below 25 K after the CDW transition with TCDW=31 K. The origin of suppression is discussed in terms of the imperfect nesting originating from the increase in the interchain transfer integral, the significant deviation from the third-order commensurability, as well as the bandwidth broadening for both TTF and TCNQ stacks. The complete suppression of the CDW phase is expected near 9 GPa.
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  • Ken-ichi Sasaki, Jie Jiang, Riichiro Saito, Seiichiro Onari, Yukio Tan ...
    2007 Volume 76 Issue 3 Pages 033702
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We present a new mechanism of carbon nanotube superconductivity that originates from edge states which are specific to graphene. Using on-site and boundary deformation potentials which do not cause bulk superconductivity, we obtain an appreciable transition temperature for the edge state. As a consequence, a metallic zigzag carbon nanotube having open boundaries can be regarded as a natural superconductor/normal metal/superconductor junction system, in which superconducting states are developed locally at both ends of the nanotube and a normal metal exists in the middle. In this case, a signal of the edge state superconductivity appears as the Josephson current which is sensitive to the length of a nanotube and the position of the Fermi energy. Such a dependence distinguishs edge state superconductivity from bulk superconductivity.
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  • Ryusuke Kondo, Momoka Higa, Seiichi Kagoshima
    2007 Volume 76 Issue 3 Pages 033703
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Non-ohmic transport was studied by pulse method in the charge-ordered state of the organic conductor θ-(BEDT-TTF)2CsZn(SCN)4 as controlling the electronic state by uniaxial strain method. It was discovered that the non-ohmic conduction under high electric fields lead to the meta-stable state with a structural modification, where the ohmic resistance was reduced to be smaller than the original. The response of the CO state to pulsed electric fields suggested a possible internal deformation of the ordered charge’s lattice.
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  • Yasuyuki Ishii, Masafumi Tamura, Reizo Kato
    2007 Volume 76 Issue 3 Pages 033704
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Static magnetic measurements have been applied for the pressure-induced superconducting state in the P21m phase of EtMe3P[Pd(dmit)2]2 (Et = C2H5, Me = CH3 and dmit2− = 1,3-dithiol-2-thione-4,5-dithiolate, C3S52−), which exhibits valence bond (VB) ordering with a spin gap at ambient pressure. Evidence for bulk superconductivity is given. The pressure dependence of the transition temperature (Tc) is obtained in the pressure range 0.2–0.5 GPa. A possible relation between the VB order and the superconductivity is suggested on the basis of the phase diagram. The nonlinear magnetization process is analyzed to determine the behavior of the lower critical field (Hc1).
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  • Yoko Miura, Yukio Yasui, Masatoshi Sato, Naoki Igawa, Kazuhisa Kakurai
    2007 Volume 76 Issue 3 Pages 033705
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    A new-type structural transition has been found in Li2RuO3 with a honeycomb lattice of edge-sharing RuO6 octahedra. With decreasing temperature T, the electrical resistivity exhibits an anomalous increase at T=Tc∼540 K, suggesting the (metal-to-insulator)-like transition, and the magnetic susceptibility also shows a sharp decrease. Detailed structure analyses have revealed that the high-temperature space group C2⁄m changes to P21m at Tc. The most striking fact is that a significant reduction of the bond lengths is found between two of the six Ru–Ru pairs of the hexagon in the low-temperature phase, indicating a new-type phase transition driven by the formation of the molecular orbits of these Ru–Ru pairs.
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  • Y. Muro, M. Ishikawa, K. Hirota, Z. Hiroi, N. Takeda, N. Kimura, H. Ao ...
    2007 Volume 76 Issue 3 Pages 033706
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We have studied the crystalline electric-field effect of the noncentrosymmetric heavy-fermion antiferromagnet CeRhSi3 by measuring the magnetic susceptibility χ(T), specific heat Cp(T) and inelastic neutron scattering. The 4f level scheme determined from χ agrees with a magnetic excitation observed in the inelastic neutron spectra and the Schottky anomaly in the magnetic part of Cp. Moreover, we have measured Cp under various magnetic fields B up to 8 T and observed that the Néel temperature TN decreases proportionally to B2 for B||a-axis while the B dependence of TN is rather small for B||c-axis. This anisotropic behavior suggests that the antiferromagnetically ordered moments lie in the tetragonal c-plane.
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  • J. T. Okada, T. Ekino, Y. Yokoyama, T. Takasaki, Y. Watanabe, S. Nanao
    2007 Volume 76 Issue 3 Pages 033707
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Theoretical studies have predicted that quasicrystals (QCs) have conspicuously fine electronic structures near the Fermi level (EF); the density of states (DOS) consists of sharp peaks and deep valleys with several 10 meV intervals. These fine electronic structures are believed to explain the unusual sensitivity of the electrical conductivity to slight changes in the chemical composition of QCs. We have investigated the DOS around the EF on single grains of icosahedral (i-)AlCuFe, i-AlPdMn, and decagonal (d-)AlCuCo QCs by break-junction tunneling spectroscopy at 4.2 K. Well-defined and reproducible pseudogaps at the EF are observed for these alloys. This is a direct experimental result that confirms the fine electronic structure existing in the vicinity of the EF.
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  • Shigeru Takagi, Shu Ishihara, Satoru Saitoh, Hiko-ichiro Sasaki, Hiros ...
    2007 Volume 76 Issue 3 Pages 033708
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The still unidentified hidden order (HO) phase below T0=17.5 K in the heavy-electron superconductor URu2Si2 has been investigated by 29Si NMR on a single crystal under external magnetic field Hext||c-axis and ambient pressure P. For a previously proposed model of the small-moment antiferromagnetism (SMAF), in which tiny-moment antiferromagnetism (AF) under ambient P is ascribed to spatially homogeneous AF with an ordered moment μSMAF=0.02–0.04 μB, splitting of the line would be expected on the basis of a scaling from the corresponding splitting in the P-induced AF. However, we observed at T=4.5 K no splitting of the line. This clearly indicates that the SMAF model cannot describe the ambient-P properties. Below T0 down to ∼14 K, the 29Si NMR line shows additional broadening over the paramagnetic width. The additional contribution, however, disappears below ∼14 K, which indicates that the HO itself produces almost zero internal field at the 29Si site along the c-axis at low temperatures in the HO phase.
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  • Ryogo Hirota, Yasuhiro Ohta
    2007 Volume 76 Issue 3 Pages 034001
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We discretize a new type of soliton equations, in which the phase shifts induced by collisions of solitons depend on the mutual positions of solitons at initial time. N-soliton solution to the discrete equations is given in the form of pfaffian.
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  • Ikuko N. Motoike
    2007 Volume 76 Issue 3 Pages 034002
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    In the present paper, I propose a simple generic discretized model for the formation of various patterns based on a reaction–diffusion model of the growth patterns of bacterial colonies. Bacterial colonies show several patterns, with a characteristic pattern being a branching dendritic one with various branch densities. In addition to living systems, these branching patterns can also be observed in physical and chemical systems. Several reaction–diffusion models have been proposed to describe their formation. The model proposed here is a simplified discretized one based on previous models and involves three variables; namely, activators, inactivators, and the substrate. By changing only the mobility of the activators and the initial substrate, the proposed model can reproduce different patterns that are based on the branching patterns. I also investigate the characteristics of the shape and growth rate of the pattern formation.
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  • Yoshimasa Matsuno
    2007 Volume 76 Issue 3 Pages 034003
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We show that the analytic N-soliton solution of the Camassa–Holm (CH) shallow-water model equation converges to the nonanalytic N-peakon solution of the dispersionless CH equation when the dispersion parameter tends to zero. To demonstrate this, we develop a novel limiting procedure and apply it to the parametric representation for the N-soliton solution of the CH equation. In the process, we use Jacobi’s formula for determinants as well as various identities among the Hankel determinants to facilitate the asymptotic analysis. We also provide a new representation of the N-peakon solution in terms of the Hankel determinants.
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  • K. Yakubo, M. Mitobe
    2007 Volume 76 Issue 3 Pages 034004
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We study statistical fluctuations of fractality of infinitely spanning clusters in bond percolation systems at the percolation threshold pc formed on two-dimensional square lattices by introducing a quantity Γ representing non-fractality of a given cluster. The distribution function of Γ reveals that most of critical clusters do not take fractal structures in the thermodynamic limit while typical structure in all possible clusters having various values of Γ is fractal (Γ=0). The existence of non-fractal critical clusters is also supported by the system size dependence of the strength of the fluctuations in fractal dimensions of clusters. It is plausible that such a large fluctuation in fractality is a common feature of disorder-induced critical phenomena.
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  • Yousuke Takeuchi, Hiroyuki Mori
    2007 Volume 76 Issue 3 Pages 034401
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We numerically investigated the collapse of one-dimensional boson–fermion mixtures with fermion–boson attractive interactions. With Monte Carlo simulations, we observed spatial distributions of the particles and the behavior of several physical quantities to find the evidence of the collapse. With strong fermion–boson attractions and weak interboson repulsions, almost all the bosons and a part of the fermions were found to gather in a small space. In this collapse process we identified the role of each microscopic parameter such as boson number density, total number densities of the fermions and the bosons, and the interboson repulsion. We show a phase diagram to locate the collapsed phase in the parameter space of the interactions.
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  • Kenji Miyamoto, Akiyoshi Hatayama, Kazuyuki Furuya
    2007 Volume 76 Issue 3 Pages 034501
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The effect of fast plasma flows on volume recombination including molecular activated recombination (MAR) in detached divertor plasma is theoretically investigated by solving particle balance equations for plasma, neutral particles, and ions. In the calculation model, the divertor region is divided into two regions, namely, region I with a high electron temperature of 10 eV and region II with a low electron temperature of 1 eV. The ion temperatures are assumed to be equal to the electron temperatures. When the plasma flows are not sufficiently slowed, for example, for plasma Mach numbers of M=0.7 in region I and M=0.5 in region II, the plasma sink due to volume recombination is less than 10% of the ion flux into region II. This means that volume recombination cannot contribute to the sink of ion fluxes even with the effect of MAR. The effects of the characteristic length of region II and the H2 temperature on MAR are also discussed.
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  • Seiji Hiramatsu, Yasushi Ishii
    2007 Volume 76 Issue 3 Pages 034601
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Vibrational spectra of realistic structural models for ternary Al–Ni–Co decagonal quasicrystals are studied. A bunch of dispersion-less modes is obtained above a few meV, which is extremely low in comparison with usual optic modes. Analyzing the local vibrational density of states at an individual atomic site, we identify several Al sites where low- and high-frequency vibrations are localized. The localized vibrations are attributed to the strong Al–TM interaction and the local atomic arrangements realized in the complex structures. Low-frequency dispersion-less modes are of special interest in relation to the phason degrees of freedom in QC but no signature of large atomic motion causing the phasonic tile flip is obtained in the low-frequency localized vibrational modes.
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  • Hiroshi Kawai, Osamu Narikiyo, Kensuke Matsufuji
    2007 Volume 76 Issue 3 Pages 034602
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The phase transition between c(4×2) and p(2×2) structures on heavily doped n-type Si(001) substrates at low temperatures under observation by the scanning tunneling microscopy is theoretically investigated. The model potential of the dimer system on the Si(001) surface is improved with an additional term which depends on temperature and the surface electric field. We show that the torque applied by the additional surface electric field introduced by the scanning tunneling microscopy causes the transformation of the c(4×2) phase, that is realized in the absence of the observation, to the p(2×2) phase on the Si(001) substrates. At higher temperatures, the c(4×2) phase is recoverd by the reduction of the additional surface electric field. The broad phase transition between the c(4×2) and p(2×2) phases is reproduced by the Monte Carlo simulations on a system with the type-C defects. We show that the broad temperature range of the phase transition is induced by the type-C defects.
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  • Sachiko T. Nakagawa
    2007 Volume 76 Issue 3 Pages 034603
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    In order to analyze atomistic defects or resultant phase transitions caused by an external or an internal disturbance, we have proposed a numerical methodology termed pixel mapping (PM) on the basis of crystallography. This method was first used for a diamond-type crystal [Phys. Rev. B 66 (2002) 094103], to quantify the mesoscopic or macroscopic structural changes in crystals from microscopic information about atomistic redistribution, which is supplied in the form of digital data obtained by a molecular dynamics simulation. We have analyzed point defects, agglomerated defects, and crystalline-to-amorphous transitions by defining a long-range-order parameter that characterizes the degree of perfection of a crystal. The major advantage of the PM method is a coarse-grained methodology by which the Miller indices of planar defects are defined. In this study, we have extended the PM method to cover the 24 prototypes of cubic crystals listed in the StrukturBericht database and we present the PM Table for those prototypes. Because of the great variety of prototypes, it is possible to discover the emergence of a new crystalline structure and antiphase domains in compound crystals, in addition to the phase transitions discussed for monatomic crystals. The use of the PM method to detect planar or linear defects with low Miller indices is presented to illustrate the power of the technique.
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  • Dai S. Hirashima
    2007 Volume 76 Issue 3 Pages 034701
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Dynamical spin susceptibilities in the chiral p-wave superconducting state, the most probable pairing state in Sr2RuO4, are calculated taking proper account of contributions from collective excitations. It is found that a spin wave mode appears in dynamical transverse susceptibility. The spin wave mode is gapped by spin–orbit interaction, but its frequency in the long wavelength limit can remain at the order of gap frequency when the anisotropy caused by spin–orbit interaction is small. The observability of the spin wave mode in a neutron scattering experiment is discussed.
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  • Y. H. Matsuda, T. Inami, K. Ohwada, Y. Murata, H. Nojiri, Y. Murakami, ...
    2007 Volume 76 Issue 3 Pages 034702
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The magnetic field-induced valence transition in YbInCu4 has been studied by X-ray absorption spectroscopy at the Yb LIII-edge up to 41 T. The field-induced valence transition is clearly observed as a significant change in the absorption spectra. Magnetic field dependences of Yb valence at low temperatures are directly determined for the first time. It is found that the valence above the metamagnetic transition recovers from Yb2.84+ to Yb2.96+ which is identical to that in the high-temperature phase. Variation of the valence is also obtained in the BT (magnetic field-temperature) plane at 0<B<41 T and 5<T<50 K.
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  • Nobuaki Takahashi, Bold Gombojav, Takehisa Yoshinari, Yoshio Takahashi ...
    2007 Volume 76 Issue 3 Pages 034703
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The dry powder of β-cyclodextrin including a pyrene single molecule and that of γ-cyclodextrin including twin molecules were prepared under vacuum. The luminescence spectra of pyrene single molecules, twin molecules and single crystals, and their temperature dependences were measured with great care in the process of cooling the samples. It is found that the features of luminescence spectra at 2 K are quite different from each other. Pyrene twin molecules in γ-cyclodextrin show an excimer luminescence similar to that of single crystal. The vibronic luminescence in the range of 3.0–3.5 eV comes from the ground-excited-state complex, or in other words, from the vibronic exciton, in contrast to the hitherto-assigned luminescence from another type of selftrapped exciton or metastable B-state which is the precursor of selftrapped excitons.
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  • Shigenori Utsumi, Daisuke Yoshiba, Nobuyuki Momozawa
    2007 Volume 76 Issue 3 Pages 034704
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Neutron diffraction experiments were carried out on single crystals of (Ba1−xSrx)2Zn2Fe12O22 at 8 K, where x is the Sr concentration ranging from 0 to 1.0. Competition of three superexchange interactions exists among Fe magnetic moments present in the 4th, 5th, and 8th layers of Sr-rich crystals. This competition leads to a distorted helimagnetic structure consisting of large and small ferrimagnetic bunches. The relations between exchange integrals J45, J48, and J58 are determined by using the molecular field approximation as J45J58=0.3657+0.0190x+0.0617x2 and J48J58=0.5047+0.0104x+0.0116x2 at 8 K. These relations provide a clear interpretation for the magnetic structure of the (Ba1−xSrx)2Zn2Fe12O22 system. Zn ion distributions in the tetrahedral sites and a local lattice deformation around Sr ions are also discussed in detail.
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  • Hiroki Nakano, Yoshinori Takahashi, Masatoshi Imada
    2007 Volume 76 Issue 3 Pages 034705
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The Drude weight of the Hubbard model on the two-dimensional square lattice is studied by the exact diagonalizations applied to clusters up to 20 sites. We carefully examine finite-size effects by consideration of the appropriate shapes of clusters and the appropriate boundary condition beyond the limitation of employing only the simple periodic boundary condition. We successfully capture the behavior of the Drude weight that is proportional to the squared hole doping concentration. Our present result gives a consistent understanding of the transition between the Mott insulator and doped metals. We also find, in the frequency dependence of the optical conductivity, that the mid-gap incoherent part emerges more quickly than the coherent part and rather insensitive to the doping concentration in accordance with the scaling of the Drude weight.
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  • Yukio Yasui, Yusuke Kobayashi, Minoru Soda, Taketo Moyoshi, Masatoshi ...
    2007 Volume 76 Issue 3 Pages 034706
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    For the fictitious spin-1/2 kagomé staircase system Co3V2O8, magnetic field–temperature (HT) phase diagrams have been constructed for the fields along three principal directions up to 5 T, using results of various macroscopic measurements on single crystal samples and also using neutron diffraction data taken on both powder and single crystal samples under H along c. In zero magnetic field, the system exhibits three transitions at temperatures Tc1∼11.2 K, Tc2∼8.8 K and Tc3∼(6.0–7.0) K. The single crystal data present clear evidence for the noncollinear nature of the magnetic structures in all magnetically ordered phases below Tc1. The sinusoidal nature of the incommensurate modulation of the ordered moment reported in the former work has been confirmed between Tc1 and Tc2, that is, no higher harmonics of the modulation have been detected even for the present large single crystal. Even in the phase of commensurate modulation between Tc2 and Tc3, we have not detected any higher harmonics of the modulation. The phase diagrams show that the magnetically ordered phases sensitively change to other phases with H, indicating that the geometrical frustration inherent in this system is important for the determination of the phase diagram. No evidence for ferroelectric transitions has been observed in the measurements of the dielectric constant (ε) applying the electric fields along three crystallographic axes, a, b, and c. Only small dielectric anomalies closely connected with the magnetic phase transitions have been found.
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  • Hideki Kumazaki, Dai S. Hirashima
    2007 Volume 76 Issue 3 Pages 034707
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The effects of impurities on the magnetism of electrons on a half-filled honeycomb lattice are studied using the self-consistent T-matrix approximation and an exact diagonalization analysis. Staggered susceptibility is found to be enhanced by vacancies; it logarithmically diverges as T→0 even in the absence of electron–electron interaction. It is found that this strong enhancement of staggered susceptibility is brought about by resonance states at zero energy (zero modes) induced by vacancies. Possible magnetic states induced by vacancies are discussed.
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  • Eiji Tsuchida
    2007 Volume 76 Issue 3 Pages 034708
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We present a novel algorithm which can overcome the drawbacks of the conventional linear scaling method with minimal computational overhead. This is achieved by introducing additional constraints, thus eliminating the redundancy of the orbitals. The performance of our algorithm is evaluated in ab initio molecular-dynamics simulations as well as in a model system.
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  • Momoka Higa, Ryusuke Kondo, Seiichi Kagoshima, Hiroyuki Nishikawa
    2007 Volume 76 Issue 3 Pages 034709
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We performed the crystal structure analyses of the pressure-induced organic superconductor β″-(DODHT)2PF6 (DODHT denotes (1,4-dioxane-2,3-diyldithio)dihydrotetrathiafulvalene) at the hydrostatic pressures of 0.75 GPa and 1.9 GPa in order to investigate the key parameter for inducing the superconductivity. At ambient pressure, β″-(DODHT)2PF6 undergoes an insulator-to-insulator transition at 255 K accompanied by charge ordering. By applying pressure, this charge-ordering transition is suppressed and superconductivity is generated at around 3 K above 1.32 GPa. Using the obtained atomic coordinates, we estimated the transfer integrals t and intermolecular nearest-neighbor Coulomb interaction energies V between conduction electrons and found that one of V⁄|t| ratios perpendicular to charge-ordering stripes plays an important role in suppressing the charge-ordering phase.
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  • Masaki Miura, Seiji Higashitani, Katsuhiko Nagai
    2007 Volume 76 Issue 3 Pages 034710
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We discuss the electronic Raman spectra of the quasi-two-dimensional spin-triplet superconductor Sr2RuO4. The order parameter is assumed to have the orbital symmetry kx±iky and sinkx±isinky. The Raman spectra are calculated using the Keldysh Green’s function theory taking into account the order parameter collective mode. We also take into account the effect of impurity scattering. The order parameter collective modes in the two paring states give sizable contribution to the Raman spectra for the B1g and B2g modes. In the kx±iky state, since the energy gap is isotropic, the B1g and B2g spectra are the same. In the sinkx±isinky state, the anisotropy of the gap yields significant mode dependence in the Raman spectra. The impurity scattering gives rise to considerable modification of the contribution from the quasiparticle excitations to the Raman spectra and simultaneously to the broadening of the collective-mode resonance peak and the shift of the peak position.
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  • Akito Kobayashi, Shinya Katayama, Yoshikazu Suzumura, Hidetoshi Fukuya ...
    2007 Volume 76 Issue 3 Pages 034711
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    The electronic states in two-dimensional organic conductor α-(BEDT-TTF)2I3 have been investigated to show the noticeable property of the massless fermions, i.e., the linear dispersion which exists on the contact point between the conduction band and the valence band. These fermions are well known in bismuth and graphite, where the former are described by the Dirac equation and the latter obeys the Weyl equation corresponding to the massless fermion. In the present study, we show that the effective Hamiltonian describing the massless fermions in α-(BEDT-TTF)2I3 contains intrinsically new terms of Pauli matrices σz and σ0 in addition to the Weyl equation which consists of σx and σy. The new massless fermions are robust against the charge disproportionation, and induce the anomalous momentum-dependence in the charge density.
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  • Satoshi Fujimoto
    2007 Volume 76 Issue 3 Pages 034712
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We present the microscopic Fermi liquid theory for magnetic properties and transport phenomena in interacting electron systems without inversion symmetry both in the normal state and in the superconducting state. Our argument is mainly focused on the application to noncentrosymmetric heavy fermion superconductors. The transport coefficients for the anomalous Hall effect, the thermal anomalous Hall effect, the spin Hall effect, and magnetoelectric effects, the existence of which is a remarkable feature of parity violation, are obtained by taking into account electron correlation effects in a formally exact way. Moreover, we demonstrate that the temperature dependence of the spin susceptibility which consists of the Pauli term and van-Vleck-like term seriously depends on the details of the electronic structure. We give a possible explanation for the recent experimental result obtained by the NMR measurement of CePt3Si [Yogi et al.: J. Phys. Soc. Jpn. 75 (2006) 013709], which indicates no change of the Knight shift below the superconducting transition temperature for any directions of a magnetic field.
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  • Takashi Hotta
    2007 Volume 76 Issue 3 Pages 034713
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    In order to clarify possible multipole states of Sm-based filled skutterudite compounds, we investigate multipole susceptibility of a multiorbital Anderson model dynamically coupled with Jahn–Teller phonons by using a numerical renormalization group method. Here we take a procedure to maximize the multipole susceptibility matrix to determine the multipole state. When the electron–phonon coupling term is simply ignored, it is found that the dominant multipole state is characterized by 2u octupole for the Γ67 quartet ground state, while the low-temperature phase is governed by magnetic fluctuations for the Γ5 doublet ground state. When we include the coupling between f electrons in degenerate Γ67 (eu) orbitals and Jahn–Teller phonons with Eg symmetry, the mixed multipole state with 4u magnetic and 5u octupole moments is found to be dominant with significant 3g quadrupole fluctuations at low temperatures.
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  • Masatomo Uehara, Takahiro Yamazaki, Tatsuya Kôri, Takeshi Kashid ...
    2007 Volume 76 Issue 3 Pages 034714
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    CdCNi3 is a newly synthesized superconductor with Tc=2.5–3.2 K. The crystal has the same perovskite-type structure as MgCNi3 but the lattice constant is ∼1% larger than that of MgCNi3. For this material, superconducting parameters, lower critical field Hc1(0), upper critical field Hc2(0), coherence length ξ(0), penetration depth λ(0), Ginzburg–Landau parameter κ(0), electronic specific heat coefficient γ, and Debye temperature ΘD have been experimentally determined. Also, full-potential augmented plane wave band calculation has been performed for CdCNi3. From experimental and band calculation results, it has been suggested that the smaller density of states at the Fermi energy and enhanced ferromagnetic correlation reduce the Tc of CdCNi3, compared with that of MgCNi3.
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  • Takeshi Nakanishi, Takeo Kato
    2007 Volume 76 Issue 3 Pages 034715
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    Thermoelectric power due to coherent electron transmission through a quantum dot is theoretically studied. In addition to the known features related to resonant peaks, we show that a novel significant structure appears between the peaks. This structure arises from the so-called transmission zero, which is characteristic of coherent transmission through several quantum levels. Because of sensitivity to the phase-breaking effect in quantum dots, this novel structure indicates the degree of coherency in the electron transmission.
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  • Yusuke Fujihara, Akihisa Koga, Norio Kawakami
    2007 Volume 76 Issue 3 Pages 034716
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We investigate the one-dimensional Hubbard model with a confining potential, which may describe cold fermionic atoms trapped in an optical lattice. Combining the variational Monte Carlo simulations with the new stochastic reconfiguration scheme proposed by Sorella, we present an efficient method to systematically treat the ground state properties of the confined system with a site-dependent potential. By taking into account intersite correlations as well as site-dependent on-site correlations, we are able to describe the coexistence of the metallic and Mott insulating regions, which is consistent with other numerical results. Several possible improvements of the trial states are also addressed.
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  • Hiroshi Sakai, Katsunori Wakabayashi, Yositake Takane
    2007 Volume 76 Issue 3 Pages 034717
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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    We have numerically studied the electronic transport properties of quantum wires with symplectic symmetry based on the tight-binding model. The asymptotic behavior of the conductance crucially depends on the even–odd effect of the conducting channel, since one perfectly conducting channel exists only in the odd-channel system. The decay length of the conductance and the distribution of the largest transmission eigenvalues clearly show the even–odd difference. Our results are in excellent agreement with the random-matrix theory.
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  • K. H. Chang, K.-G. Park, K.-D. Ahan, Soo Yong Kim, Deock-Ho Ha, Kyungs ...
    2007 Volume 76 Issue 3 Pages 035001
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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  • K. S. Kim
    2007 Volume 76 Issue 3 Pages 035002
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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  • Takafumi Kita
    2007 Volume 76 Issue 3 Pages 038001
    Published: March 15, 2007
    Released on J-STAGE: August 12, 2010
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