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- Proceedings of the Physico-Mathematical Society of Japan. 3rd Series
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Volume 77, Issue 7
Displaying 1-50 of 59 articles from this issue
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Rinto Anugraha, Yoshiki Hidaka, Noriko Oikawa, Shoichi Kai2008 Volume 77 Issue 7 Pages 073001
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThis Letter reports a transition to spatiotemporal chaos (STC) in an electroconvective system of a homeotropic nematic liquid crystal under a symmetry breaking. The homeotropic system has a continuous symmetry which leads to the occurring of STC at a threshold for convection. When the symmetry is broken by an external field, a periodic pattern appears first and then STC appears at a higher transition point. The transition from the periodic pattern to STC is investigated by order parameters which were obtained from spectra of convective patterns. The results are compared with the recent theoretical researches for the damped Nikolaevskiy equation.View full abstractDownload PDF (196K) -
Masami Tsubota, Satoshi Tsutsui, Daisuke Kikuchi, Hitoshi Sugawara, Hi ...2008 Volume 77 Issue 7 Pages 073601
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe detailed crystal structure of a mixed-valent skutterudite SmOs4Sb12 has been investigated by synchrotron radiation powder diffraction. Although the lattice parameter monotonically decreases with decreasing temperature, Sm–Sb bond length decreases rapidly below 150 K. The temperature dependence of the bond length coincides with that of the change in the valence of the Sm ion. These facts suggest that the hybridization between 4f- and conduction electrons is enhanced at low temperatures. In addition, an isotropic thermal atomic displacement parameter of the Sm ion is much larger than those of the Os and Sb ions. This fact indicates the presence of an anharmonic vibration of Sm ions.View full abstractDownload PDF (128K) -
Akihisa Koga, Takuji Higashiyama, Kensuke Inaba, Seiichiro Suga, Norio ...2008 Volume 77 Issue 7 Pages 073602
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study ultracold fermionic atoms trapped in an optical lattice with harmonic confinement by dynamical mean-field approximation. It is demonstrated that a supersolid state, where an s-wave superfluid coexists with a density-wave state with a checkerboard pattern, is stabilized by attractive onsite interactions on a square lattice. Our new finding here is that a confining potential plays an invaluable role in stabilizing the supersolid state. We establish a rich phase diagram at low temperatures, which clearly shows how an insulator, a density wave and a superfluid compete with each other to produce an interesting domain structure. Our results shed light on the possibility of the supersolid state in fermionic optical lattice systems.View full abstractDownload PDF (366K) -
Yusuke Nakai, Kenji Ishida, Yoichi Kamihara, Masahiro Hirano, Hideo Ho ...2008 Volume 77 Issue 7 Pages 073701
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the iron-based layered LaFeAs(O1−xFx) (x=0.0, 0.04, and 0.11). In the undoped LaFeAsO, 1⁄T1 of 139La exhibits a distinct peak at TN∼142 K below which the spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the 4% F-doped sample, 1⁄T1T exhibits a Curie–Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the 11% F-doped sample, in contrast, pseudogap behavior is observed in 1⁄T1T both at the 75As and 139La site with a gap value of ΔPG∼172 K. The spin dynamics vary markedly with F doping, which is ascribed to the Fermi-surface structure. As for the superconducting properties for the 4 and 11% F-doped samples, 1⁄T1 in both compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures, which suggests unconventional superconductivity with line-nodes. We discuss similarities and differences between LaFeAs(O1−xFx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F doping dependence of Tc and 1⁄T1.View full abstractDownload PDF (251K) -
Yoshihiko Ihara, Kenji Ishida, Hiroto Ohta, Kazuyoshi Yoshimura2008 Volume 77 Issue 7 Pages 073702
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSCo-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on a c-axis-aligned crystalline sample of cobaltate superconductor Nax(H3O)zCoO2·yH2O. The sample properties were characterized in detail by using the NMR and NQR measurements, and the sample was confirmed to exhibit a clear superconducting transition at Tc=4.56 K. The external field direction was controlled by rotating the sample at low temperatures. The detailed analyses of the NMR spectra revealed that the c-axis direction of the crystalline sample was distributed within ±2.5°. The relaxation rate divided by temperature 1⁄T1T and Knight shift were measured in the superconducting state. The Knight shift decreased by approximately 0.015% below Tc, which is almost one order smaller than those reported previously. The value of the decrease was the same order as the superconducting diamagnetic effect. The quantitative discussion is given to the Knight shift in the superconducting state.View full abstractDownload PDF (238K) -
Elena Hassinger, Dai Aoki, Georg Knebel, Jacques Flouquet2008 Volume 77 Issue 7 Pages 073703
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSRecently, coexistence of ferromagnetism (TCurie=2.8 K) and superconductivity (Tsc=0.8 K) has been reported in UCoGe, a compound close to a ferromagnetic instability at ambient pressure P. Here we present resistivity measurements under pressure on a UCoGe polycrystal. The phase diagram obtained from resistivity measurements on a polycrystalline sample is found to be qualitatively different to those of all other ferromagnetic superconductors. By applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No indication of ferromagnetic order has been observed above P≈1 GPa. The resistive superconducting transition is, however, quite stable in temperature and persists up to the highest measured pressure of about 2.4 GPa. Superconductivity would therefore appear also in the paramagnetic phase. However, the appearance of superconductivity seems to change at a characteristic pressure P\\star∼0.8 GPa. Close to a ferromagnetic instability, the homogeneity of the sample can influence strongly the electronic and magnetic properties and therefore bulk phase transitions may differ from the determination by resistivity measurements.View full abstractDownload PDF (320K) -
Gaku Motoyama, Aya Tamura, Yasukage Oda2008 Volume 77 Issue 7 Pages 073704
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA typical magnetic aftereffect is observed in the exchange-enhanced paramagnetic compound TiCo. This indicates that the sample contains a small number of ferromagnetic clusters, the sizes of which are near the critical value for the magnetic aftereffect. The extremely long relaxation time of the magnetization of the ferromagnetic clusters is responsible for the abnormal hysteresis in the temperature dependence of susceptibility reported previously. The size and number of ferromagnetic clusters may be related to the superconducting transition temperature.View full abstractDownload PDF (220K) -
Rikio Settai, Yuichiro Miyauchi, Tetsuya Takeuchi, Florence Lév ...2008 Volume 77 Issue 7 Pages 073705
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe measured low-temperature electrical resistivity in a magnetic field as a function of pressure, and studied the superconducting property of CeIrSi3 with a non-centrosymmetric tetragonal structure. CeIrSi3 is an antiferromagnet with a Néel temperature TN=5.0 K at ambient pressure, but the antiferromagnetic ordering disappears completely at a pressure Pc=2.25 GPa. Superconductivity appears in a wide pressure region from 1.8 to about 3.5 GPa, with a maximum transition temperature Tsc\\simeq1.6 K at Pc*\\simeq2.63 GPa. At around Pc*, the upper critical field Hc2 for the magnetic field H along the [0 0 1] direction is not destroyed by spin polarization based on Zeeman coupling but possesses an upturn curvature below 1 K, revealing a divergent tendency of Hc2 at Pc*, with a huge Hc2(0)\\simeq450 kOe. On the other hand, the upper critical field for H||[110] indicates the tendency of Pauli paramagnetic suppression, with Hc2(0)=95 kOe at 2.65 GPa. This might be a combined phenomenon between the electronic instability at Pc* and the characteristic superconducting property without inversion symmetry in the tetragonal structure.View full abstractDownload PDF (182K) -
Chul-Ho Lee, Akira Iyo, Kunihiro Kihou, Hijiri Kito, Haruhiro Hiraka, ...2008 Volume 77 Issue 7 Pages 073706
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSEvidence of long-range magnetic ordering in underdoped superconducting HgBa2Ca4Cu5O12+δ has been sought by the powder neutron diffraction technique. Within instrumental sensitivity, no clear magnetic Bragg peak was observed. We discuss the possible magnetic ordered state in relation to a recent study of this system by NMR.View full abstractDownload PDF (311K) -
Atsushige Ikeda, Hikaru Kawamura2008 Volume 77 Issue 7 Pages 073707
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe ordering of the Ising model on a pyrochlore lattice interacting via the long-range RKKY interaction, which models a metallic pyrochlore magnet such as Pr2Ir2O7, is studied by Monte Carlo simulations. Depending on the parameter kF representing the Fermi wavevector, the model exhibits rich ordering behaviors.View full abstractDownload PDF (251K) -
Satoshi Yamashita, Tatsuya Fujisaki, Yasuhiro Nakazawa, Masaharu Oguni ...2008 Volume 77 Issue 7 Pages 073708
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA low-temperature thermodynamic measurement of a single crystal of [Mn4(hmp)4(pdm)2{N(CN)2}2](ClO4)2·1.75H2O·2MeCN, which has a two-dimensional coordinating network consisting of Mn4 single-molecule magnets (SMMs), was performed by thermal relaxation calorimetry. Magnetic ordering was observed at an extremely low-temperature of 380 mK at a zero field. We have found that the temperature dependence of heat capacity is strongly affected by applying weak magnetic fields owing to the large Zeeman effect occurring in the constituting SMM unit. When magnetic fields of 0.1–0.3 T are applied, an abrupt decrease in heat capacity is observed at approximately 0.9 K, which phenomenologically resembles the glass formation of molecular or macromolecular systems. The delicate balance between the Zeeman effect in each unit and the cooperative character of a network produces such a nonequilibrium magnetic state in this material.View full abstractDownload PDF (218K) -
Taketo Moyoshi, Yukio Yasui, Yoshiaki Kobayashi, Masatoshi Sato, Kazuh ...2008 Volume 77 Issue 7 Pages 073709
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSIn neutron inelastic measurements on aligned crystals of NaxCoO2·yD2O, two magnetic peaks have been observed. One peak corresponds to the contribution of ferromagnetic fluctuations and another peak, that of antiferromagnetic fluctuations. Both have two-dimensional characteristics. The intensity of ferromagnetic fluctuation decreases with decreasing temperature T and becomes inappreciable below 25 K. In contrast, antiferromagnetic fluctuation remains finite at 5 K. We have also carried out specific heat measurements on several samples with different values of the 59Co-nuclear quadrupole frequency (νQ) within the region 12.0<νQ3≅3νQ<12.9 MHz, where the superconducting, nonsuperconducting and superconducting phases appear in the transition temperature (Tc)–νQ3 phase diagram with varying νQ3, and found that the electronic specific heat coefficient γ does not change so significantly as to indicate a topological change of the Fermi surface with νQ. These results imply that hole pockets, the existence of which is suggested by band calculations near the K points in the reciprocal space, do not exist in the entire superconducting νQ3 region and support that the superconducting pair symmetry does not change with νQ3 in the phase diagram.View full abstractDownload PDF (202K) -
Shoichi Niizeki, Fumiko Yoshikane, Kentaroh Kohno, Kazuyuki Takahashi, ...2008 Volume 77 Issue 7 Pages 073710
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSDielectric response and nonlinear conduction are studied in an organic conductor β-(meso-DMBEDT-TTF)2PF6, which undergoes the metal–insulator transition caused by the checkerboard-type charge ordering (CCO). The formation of the long-range CCO (LR-CCO) was observed as a sudden increase in the dielectric constant below 70 K. Below 70 K, the I–V curve shows a remarkable negative differential resistance with a non-monotonous voltage drop, and its nonlinearity survives up to about 100 K. Time-resolved sample voltage data shows a steep drop followed by a transient plateau and a further drop into the most conductive state. The former steep voltage drop may cause the negative differential resistance in the I–V curve, while the transient plateau implies a metastable state induced by the electric field.View full abstractDownload PDF (477K) -
Hideaki Ujino, Luc Vinet, Tetsu Yajima, Haruo Yoshida2008 Volume 77 Issue 7 Pages 074001
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe maximal super-integrability of a discretization of the Calogero–Moser model introduced by Nijhoff and Pang is presented. An explicit formula for the additional constants of motion is given.View full abstractDownload PDF (76K) -
Yasunobu Nakamura2008 Volume 77 Issue 7 Pages 074002
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study a classical Ising spin system on a soccer ball lattice. The magnetic easy axis of the system is adopted parallel to the radial direction. We apply a magnetic field to this system in several directions. Ferromagnetic and antiferromagnetic nearest-neighbor interaction cases are considered. In the case of the antiferromagnetic interaction, a frustration effect is observed because of a pentagonal interaction loop. We carry out a numerical calculation for the system to obtain the ground states for various magnetic fields. A Monte Carlo simulation is also performed to compute thermodynamic quantities at finite temperatures. The obtained magnetization process has many magnetic phases reflecting the frustration effect. The thermodynamic quantities are characteristic because the Zeeman energy for each spin is different due to the geometrical property of the soccer ball.View full abstractDownload PDF (792K) -
Zonghua Liu, Baowen Li2008 Volume 77 Issue 7 Pages 074003
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study vibrational energy transport in a quasi one-dimensional (1D) harmonic chain with both longitudinal and transverse vibrations. We demonstrate via both numerical simulation and theoretic analysis that for 1D atomic chain connected by three-dimensional (3D) harmonic springs, the coefficient of heat conduction changes continuously with its lattice constant, indicating the qualitative difference from the corresponding 1D case where the coefficient is independent of the lattice constant.View full abstractDownload PDF (135K) -
Takao Ohta, Takahiro Ohkuma2008 Volume 77 Issue 7 Pages 074004
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSLinear response and fluctuation dynamics are formulated in a multi-component stochastic system far from equilibrium starting from the nonlinear Langevin equation with Gaussian white noises. It is shown that the steady probability current plays an important role for the response and time-correlation relation and violation of the time reversal symmetry. When the steady current is absent, the formulas reduce to those near thermal equilibrium.View full abstractDownload PDF (111K) -
Miki Wadati2008 Volume 77 Issue 7 Pages 074005
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA systematic method is presented for the construction of the parity-time (PT) symmetric potentials. The key idea is the transformation between Dirac type and Schrödinger type eigenvalue problems in the inverse scattering method. As a standard example, the modified Korteweg–de Vries (mKdV) equation is considered. There exists a PT symmetric potential corresponding to a soliton solution. One- and two-soliton PT symmetric potentials are given explicitly. The extensions of the theory into other types of solutions and other soliton equations are discussed.View full abstractDownload PDF (84K) -
Takeya Tsurumi2008 Volume 77 Issue 7 Pages 074006
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe propagation of electromagnetic waves in magnetic metamaterials is studied. Magnetic metamaterials are composed of split-ring resonators (SRRs) whose capacitance shows nonlinearities and random fluctuations. Applying reductive perturbation analysis to time evolution equations for voltages in SRRs, the nonlinear Schrödinger equation with a stochastic term is derived. By taking the statistical average of a one-soliton solution, the deformation of a soliton during propagation due to microscopic disorder is investigated.View full abstractDownload PDF (154K) -
Takuya Iwashita, Yasuya Nakayama, Ryoichi Yamamoto2008 Volume 77 Issue 7 Pages 074007
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe present a numerical method that consistently implements thermal fluctuations and hydrodynamic interactions to the motion of Brownian particles dispersed in incompressible host fluids. In this method, the thermal fluctuations are introduced as random forces acting on the Brownian particles. The hydrodynamic interactions are introduced by directly resolving the fluid motions with the particle motion as a boundary condition to be satisfied. The validity of the method has been examined carefully by comparing the present numerical results with the fluctuation–dissipation theorem whose analytical form is known for dispersions of a single spherical particle. Simulations are then performed for more complicated systems, such as a dispersion composed of many spherical particles and a single polymeric chain in a solvent.View full abstractDownload PDF (473K) -
Chong-Sa Lim, Nobuhito Maru, K. Hasegawa2008 Volume 77 Issue 7 Pages 074101
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe calculate one-loop radiative correction to the mass of Higgs identified with the extra space components of the gauge field in a six-dimensional massive scalar QED compactified on a two-sphere. The radiatively induced Higgs mass is explicitly shown to be finite for arbitrary bulk scalar mass M. Furthermore, the remaining finite part also turns out to vanish, at least for the case of small M, thus suggesting that the radiatively induced Higgs mass exactly vanishes, in general. The non-zero “Kaluza–Klein” modes in the gauge sector are argued to have a Higgs-like mechanism and quantum mechanical N=2 supersymmetry, while the Higgs zero modes, as supersymmetric states, have a close relation with monopole configuration.View full abstractDownload PDF (235K) -
Geol Moon, Heung-Sik Noh, Heung-Ryoul Noh2008 Volume 77 Issue 7 Pages 074301
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSIn this study, we examined the effect of pump laser beam diameter on saturated absorption spectra. The rate equations describing the dynamics of the population of each sublevel were solved and the time evolution of the signals was obtained theoretically. With the exception of some signals, the experimental results showed good agreement with the calculated results, which were analyzed using the calculation based on rate equations. Furthermore, the beam diameter dependence of the spectra was examined for several pump beam intensities, and the results matched the calculated results.View full abstractDownload PDF (551K) -
Serge I. Fewo, Claude M. Ngabireng, Timoleon C. Kofane2008 Volume 77 Issue 7 Pages 074401
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWith the help of the Maxwell equations, a basic equation modeling the propagation of ultrashort optical solitons in optical fiber is derived, namely the higher-order complex Ginzburg–Landau equation (HCGLE). Considering this one-dimensional HCGLE, we obtain a set of differential equations characterizing the variation of the pulse parameters called collective variables (CVs), of a pulse propagating in dispersion-managed (DM) fiber optic-links. Equations obtained are investigated numerically in order to observe the behaviour of pulse parameters along the optical fiber. A fully numerical simulation of the one-dimensional HCGLE finally tests the results of the CV theory. A good agreement between both methods is observed. Among various behaviours, chaotic pulses, attenuate pulses and stable pulses can be obtained under certain parameter values.View full abstractDownload PDF (4337K) -
Norihiro Sei, Kawakatsu Yamada, Hiroshi Ogawa2008 Volume 77 Issue 7 Pages 074501
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe measured the bunch length of an electron beam in the macropulse mode of a storage ring free electron laser (SRFEL) with the compact storage ring NIJI-IV. The energy spread was evaluated from measured data of the bunch length. The synchrotron damping time of the electron bunch was evaluated by applying the evolution of the energy spread to an expression based on the one-dimensional theory of bunch heating. The synchrotron damping time evaluated at five electron-beam currents was in accord with that calculated by computer simulation. This finding suggests that the synchrotron damping time can be measured by the new evaluation method in the SRFEL macropulse mode. It was clarified that the synchrotron damping time measured in a Q-switching operation is shorter than that measured in the macropulse mode. This difference would suggest that the peak intensity of the SRFEL micropulse affects the synchrotron damping time.View full abstractDownload PDF (224K) -
Masahiro Ikegami, Hiroshi Sugimoto, Hiromi Okamoto2008 Volume 77 Issue 7 Pages 074502
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSLaser cooling of ion beams generally operates only upon the longitudinal motion of an ion beam. In order to extend this powerful dissipative force to the transverse directions, we consider introducing a Wien filter in a cooing straight section. It is theoretically shown that longitudinal cooling within a Wien filter naturally develops a transverse (mostly horizontal) cooling effect as well. Molecular dynamics simulations demonstrate that this method enables us to reach an ultralow-temperature state of a stored ion beam.View full abstractDownload PDF (196K) -
Man Zhao, Xiaodong Dai, Yixiong Shen, Baixin Liu2008 Volume 77 Issue 7 Pages 074601
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSFor the equilibrium immiscible Ag–Ta system characterized by a positive heat of formation of +23 kJ/mol, a proved realistic extended Finnis–Sinclair potential is applied to study the crystal-to-amorphous transition through molecular dynamics simulations and a glass-forming range (GFR) of the Ag–Ta system is determined to be from 10 to 80 at. % of Ta, within which a disordered state is energetically favored than its crystalline counterpart of solid solution. In experiment, the uniform amorphous phases are indeed obtained, by ion beam mixing of far-from-equilibrium, in the Ag38Ta62, Ag30Ta70 and Ag20Ta80 Ag–Ta multilayered films, which fall within the GFR and thus confirm the relevance of the calculated GFR of the system.View full abstractDownload PDF (954K) -
Masashi Torikai2008 Volume 77 Issue 7 Pages 074602
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA spherocylinder-like molecule with a Lennard-Jones-type interaction is proposed as a model of smectic-A (Sm-A) liquid crystals, which can form a free-standing film. By means of Gibbs ensemble simulations, the isotropic, nematic, and Sm-A phases of the model fluid are found to coexist with a vapor phase; and the coexistence conditions of the liquid crystal phases with the vapor phase are determined. For a set of the interaction-parameters of the model molecule, the Sm-A free-standing film is produced below the bulk isotropic–Sm-A phase transition temperature by using Monte Carlo simulations. The film tension of the Sm-A free-standing film is calculated and its dependencies on the temperature and on the number of molecules are discussed.View full abstractDownload PDF (254K) -
Yu Tian, Hongbing Lu, Duofa Wang, Jinchai Li, Min Shuai, Qiang Fu2008 Volume 77 Issue 7 Pages 074603
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report the realization of uniform zinc oxide (ZnO) hollow spherical structure consisting of highly radial and oriented ZnO nanorods, which results from a facile precursor-templated synthesis through thermal evaporation at a relative low temperature without any catalyst. By optimizing the experimental parameters, the obtained results demonstrate that the morphology of ZnO is very sensitive to Zn powder precursor. Detailed structural analyses confirm that this microstructure exhibits a wurtzite hexagonal phase and those nanorods are preferentially oriented along the c-axis direction. The formation mechanism of the microstructure is proposed to be a vapor–solid process. This method may provide a simple and versatile approach to large-scale production of hollow spherical ZnO structure.View full abstractDownload PDF (2813K) -
Saeed Yeganegi, Azita Amoozad Khalili, Mahshid Hamzehlooian2008 Volume 77 Issue 7 Pages 074604
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSIn this work we have performed HEX-NEMD simulations to calculate thermal diffusion factor (TDF) for binary mixtures of square well particles for a wide range of diameter ratios, well depth ratios and well width ratios for a fixed reduced density and temperature. The results show that dependence of TDF to the potential parameters is resembled to the Lennard-Jonnes mixtures. The TDF decreases with diameter ratio. However, TDF increases as the ratios of well depth, well width and mass of two particles become larger than one.View full abstractDownload PDF (98K) -
Ken-ichi Suga, Akimasa Ohnishi, Mikio Koyano, Minoru Sasaki, Koichi Ki ...2008 Volume 77 Issue 7 Pages 074605
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSMagnetic-field-induced quantum oscillation (FIQO) has been observed for η-Mo4O11 single crystals at high magnetic fields of 20–53 T. According to fast Fourier transformation analysis, we found that oscillatory frequency changes drastically at characteristic magnetic fields of 36 and 49 T. The frequencies are several orders of magnitude greater than those of Shubnikov–de Haas oscillations observed at low magnetic fields below 20 T. We discussed FIQO on the basis of the proposed mechanism in which both inert electron and hole Landau levels and nested Fermi surfaces are revived to be active by charge transfer with magnetic breakdown.View full abstractDownload PDF (331K) -
Wataru Kobayashi, Wataru Tamura, Ichiro Terasaki2008 Volume 77 Issue 7 Pages 074606
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report the thermal conductivity κ and figure of merit Z of thermoelectric rhodium oxides using a modified Harman method. κ and Z are obtained to be 30 mW/(cm·K) and 1×10−4 K−1 at 200 K, respectively, which are comparable to those of thermoelectric-layered cobalt oxides. In particular, Z=2.3×10−4 K−1 is found in the pseudo-one-dimensional Ba1.2Rh8O16 at 75 K, which is the second-best value among oxides below 300 K. We show that the modified Harman method is a convenient and powerful tool for investigating the thermoelectric properties of small crystals.View full abstractDownload PDF (153K) -
Tatsuya Yanagisawa, Pei-Chun Ho, William M. Yuhasz, M. Brian Maple, Yu ...2008 Volume 77 Issue 7 Pages 074607
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe off-center rattling of Nd rare-earth ions in the filled skutterudite compound NdOs4Sb12 has been investigated by ultrasonic measurement. The longitudinal C11 mode for frequencies between 34 and 253 MHz shows a marked frequency dependence in elastic constant and ultrasonic attenuations at two different temperatures centered at around 45 and 15 K. The relaxational frequency dependence of ultrasonic dispersion reveals a thermally activated Γ23-type off-center motion of Nd-ions, involving local charge fluctuations with Γ23 symmetry in the (OsSb3)4 cage. An attempt time τ0,(1)=7.5×10−12 s and an activation energy E1=337 K were obtained from fits to the dispersion at around 45 K. The presence of another dispersion at lower temperatures of around 15 K implies that the rattling in NdOs4Sb12 has an additional low-energy excitation characterized by a lower activation energy E2∼67 K with an attempt time τ0,(2)=5.1×10−11 s.View full abstractDownload PDF (469K) -
Akihito Takeuchi, Gen Tatara2008 Volume 77 Issue 7 Pages 074701
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe demonstrate theoretically that a charge current and a spin current are generated by spin dynamics in the presence of spin–orbit interaction in the perturbative regime. We consider a general spin–orbit interaction including the spatially inhomogeneous case. Spin current due to spin damping is identified as one origin of generated charge current, but other contributions exist, such as the one due to an induced conservative field and the one arising from the inhomogeneity of spin–orbit interaction.View full abstractDownload PDF (315K) -
Shinpei Fujii, Mitsuo Okada, Shoji Ishida, Setsuro Asano2008 Volume 77 Issue 7 Pages 074702
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSFirst-principle total-energy calculations show that a ferrimagnetic state is most stable in Mn2YZ (Y = Cr and Mn) with the Heusler structure and that among them there are highly spin-polarized ones with magnetic moments of 0, 1, and 2μB per formula unit. Electronic structures of nonstoichiometric alloys suggest that partial replacement of constituent atoms in the highly spin-polarized alloys can be made without a decrease in spin polarizaion. Our results predict that in Mn–Cr–Z alloys we may get highly spin-polarized alloys with magnetic moments per formula unit ranging from −0.8 to 2μB.View full abstractDownload PDF (243K) -
Shugo Suzuki, Ming-Fang Li, Toshihiro Ariizumi2008 Volume 77 Issue 7 Pages 074703
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study the structural, electronic, magnetic, optical, and magneto-optical properties of NpN in detail using the fully relativistic full-potential calculations based on the density functional theory within the local spin density approximation. We successfully reproduce the positive sign of the electric field gradient (EFG) at Np nuclei. The positive EFG is in striking contrast to the negative EFG in a Np3+ free ion, indicating the importance of the interplay between spin–orbit coupling and covalent bonding in NpN. Also, the calculated band structure shows large splittings induced by spin polarization and spin–orbit coupling, suggesting that both effects are indispensable for understanding the electronic properties of this material. This results in a large Kerr rotation angle of about 2°, which is comparable to those of uranium calcogenides.View full abstractDownload PDF (242K) -
Mai Yokoi, Yoshiaki Kobayashi, Taketo Moyoshi, Masatoshi Sato2008 Volume 77 Issue 7 Pages 074704
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESS59Co- and 23Na-NMR measurements have been carried out on polycrystalline and c-axis aligned samples of Na0.5CoO2, which exhibits successive transitions at temperatures T=87 K (=Tc1) and T=53 K (=Tc2). 59Co-NMR has also been carried out on c-axis aligned crystallites of K0.5CoO2 with similar successive transitions at Tc1∼60 K and Tc2∼20 K. For Na0.5CoO2, two sets of three NMR lines of 23Na nuclei, explained by considering the quadrupolar frequencies νQ∼1.32 and 1.40 MHz, have been observed above Tc1, as is expected from the crystalline structure. A rather complicated but characteristic variation of the 23Na-NMR spectra has been observed with varying T through the transition temperatures, and the internal fields at two crystallographically distinct Na sites are discussed on the basis of the magnetic structures reported previously. The internal fields at two distinct Co sites observed below Tc1 and the 591⁄T1–T curves of Na0.5CoO2 and K0.5CoO2 are also discussed in a comparative way.View full abstractDownload PDF (944K) -
Koichi Hiraoka, Akihiko Oota, Hiroyuki Jinushi2008 Volume 77 Issue 7 Pages 074705
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSZero-field 59Co NMR, X-ray diffraction (XRD) and magnetization measurements have been made to investigate the mechanical alloying (MA) of ferromagnetic Co75C25 powder as a function of milling time (MT). The MA in Co75C25 proceeds rapidly with increasing MT up to 30 h and more gradually above 30 h by both the processes of dissolving C in the Co matrix and forming a metastable phase of Co3C. XRD patterns show that the sample is in an amorphous state for MT≥50 h, and its amorphization proceeds with further increasing the milling time. NMR results show that there coexist a saturated solid solution formed by dissolving C in Co, Co3C and hcp-Co in the amorphous state and suggest that these phases consist of fine particles. The MA is not completed even for a long milling time of 100 h.View full abstractDownload PDF (212K) -
Dong-Seok Yang, Kyuseung Oh, Yong-Goo Yoo, Seong-Cho Yu2008 Volume 77 Issue 7 Pages 074706
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSFe60Ni40 metastable alloy was fabricated by the mechanical alloying process. The magnetization of the processed powder decreased gradually as the alloying time increased. The formation of the alloy was confirmed by the structural analysis. X-ray diffraction analysis showed that the long range order was remained until 6 h but disappeared after 12 h of milling. EXAFS showed that there was a substantial change in the local structure between 6 and 12 h of milling. The structural analysis showed that alloying was activated in 6 h and completed almost in 24 h. The estimated bond distance of Fe–M (M: Fe or Ni) for the final alloy was about (2.54±0.02) Å.View full abstractDownload PDF (341K) -
Keita Kishigi, Hirotoshi Hanada, Yasumasa Hasegawa2008 Volume 77 Issue 7 Pages 074707
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study the condition to open a finite gap in tight-binding electrons on an extended honeycomb lattice with the next-nearest-neighbor transfer integrals t2a, t2b, t2c, t2d, t2e, and t2f, where t2a, t2b, and t2c are transfer integrals between the sublattice A and t2d, t2e, and t2f are transfer integrals between the sublattice B. If the system has the inversion symmetry in this model, i.e., the sublattices A and B have the same on-site potential (εA=εB), the gap is zero. We find that although the finite gap is generally opened by inversion-symmetry breaking, the gap remains zero if the averaged inversion symmetry, which is defined as the sum of the transfer integrals and the on-site potentials of the sublattices are the same (t2a+t2b+t2c+εA=t2d+t2e+t2f+εB), is conserved.View full abstractDownload PDF (97K) -
Takahiro Onimaru, Yukihiro F. Inoue, Keisuke Shigetoh, Kazunori Umeo, ...2008 Volume 77 Issue 7 Pages 074708
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSElectrical resistivity ρ, magnetic susceptibility χ, magnetization M, and specific heat measurements are reported on a singlecrystalline sample of CePd5Al2, showing successive antiferromagnetic orderings at TN1=4.1 K and TN2=2.9 K. The temperature dependence of ρ shows a Kondo metal behavior with large anisotropy, ρc⁄ρa=3.2 at 20 K, and opening of a superzone gap along the tetragonal c-direction below TN1. Both TN1 and TN2 gradually increase with applying pressure up to 2.5 GPa. The data of χ(T) and M(B) in the paramagnetic state were analyzed using a crystalline electric field (CEF) model. It led to a Kramers doublet ground state with wave functions consisting primarily of |±5⁄2›, whose energy level is isolated from the excited states by 230 and 300 K. This CEF effect gives rise to the large anisotropy in the paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is manifested as Mc⁄Ma=20 in B=5 T and at 1.9 K, and χc⁄χa=25 in B=0.1 T and at 4 K. In powder neutron diffraction experiments, magnetic reflections were observed owing to the antiferromagnetic ordered states below TN1, whereas no additional reflection was found below TN2.View full abstractDownload PDF (779K) -
Kaoru Yamamoto, Shinichiro Iwai, Sergiy Boyko, Akimitsu Kashiwazaki, F ...2008 Volume 77 Issue 7 Pages 074709
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report experimental evidence for the generation of ferroelectric polarization in an organic conductor α-[bis(ethylenedithio)tetrathiafulvalene]2I3 obtained by optical second-harmonic generation. The spontaneous polarization emerges along with a metal-to-insulator transition that is driven by the Wigner crystallization of electrons. The strong optical nonlinearity and its ultrafast photoresponse demonstrated by this study exemplify the nature of the ferroelectric polarization that originates from the electron ordering.View full abstractDownload PDF (492K) -
Yuki Wakisaka, Kou Takubo, Takaaki Sudayama, Jin-Young Son, Takashi Mi ...2008 Volume 77 Issue 7 Pages 074710
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSIn order to understand the nature of chain-driven superconductivity in Pr2Ba4Cu7O15−δ (Pr247), we have studied the electronic structure of as-sintered non-superconducting Pr247 and annealed superconducting Pr247 samples using photoemission spectroscopy. The O 1s, Ba 3d, Pr 4d, and Cu 2p core-level energy shifts by annealing indicate that electrons doped by the annealing mainly fill the localized Fehrenbacher–Rice (FR) state. The photoemission spectra ρ(ω) near the Fermi level (EF) are derived from the metallic Cu–O double chain and can be fitted to the power-law function plus step function Aωα+Bθ(ω). ρ(ω) near EF is indistinguishable between the as-sintered and annealed Pr247 and the exponent α is ∼1.5. These results indicate that the Cu–O double chain provides the spectral weight near EF and that the annealing affects the localized FR state instead of the near-EF state.View full abstractDownload PDF (231K) -
Hisashi Uzu, Arata Tanaka2008 Volume 77 Issue 7 Pages 074711
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSElectronic state and the Verwey transition in magnetite (Fe3O4) are studied using a spinless three-band Hubbard model for 3d electrons on the B sites with the Hartree–Fock approximation and the exact diagonalisation method. Complex-orbital, e.g., (1⁄\\sqrt2)[|zx›+i|yz›], ordered (COO) states having noncollinear orbital moments ∼0.4 μB on the B sites are obtained with the cubic lattice structure of the high-temperature phase. The COO state is a novel form of magnetic ordering within the orbital degree of freedom. It arises from the formation of Hund’s second rule states of spinless pseudo-d molecular orbitals in the Fe4 tetrahedral units of the B sites and ferromagnetic alignment of their fictitious orbital moments. A COO state with longer periodicity is obtained with pseudo-orthorhombic Pmca and Pmc21 structures for the low-temperature phase. The state spontaneously lowers the crystal symmetry to the monoclinic and explains experimentally observed rhombohedral cell deformation and Jahn–Teller like distortion. From these findings, we consider that at the Verwey transition temperature, the COO state remaining to be short-range order impeded by dynamical lattice distortion in high temperature is developed into that with long-range order coupled with the monoclinic lattice distortion.View full abstractDownload PDF (2437K) -
Masashige Matsumoto, Takayuki Shoji, Mikito Koga2008 Volume 77 Issue 7 Pages 074712
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study magnetic excitations for anisotropic spin dimer systems. We present a theory that describes not only the lowest-lying excitation mode but also higher-lying modes of the spin dimers, where the latter modes are important for quantum phase transitions driven by magnetic field and pressure in spin-gapped systems. As the most intriguing application, we calculate electron spin resonance (ESR) intensity in the presence of Dzyaloshinskii–Moriya (DM) interaction, which couples the local triplet with the singlet states of the dimer. The ESR intensities under various configurations of the DM interactions are reported in both disordered and field-induced ordered phases, which are very useful for the analysis of high-field ESR data.View full abstractDownload PDF (683K) -
Nobuya Maeshima, Kenji Yonemitsu2008 Volume 77 Issue 7 Pages 074713
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe discuss photogenerated midgap states of a one-dimensional (1D) dimerized Mott insulator, potassium-tetracyanoquinodimethane (K-TCNQ). Two types of phonon modes are taken into account: intermolecular and intramolecular vibrations. We treat these phonon modes adiabatically and analyze a theoretical model by using the density-matrix renormalization group (DMRG). Our numerical results demonstrate that the intermolecular lattice distortion is necessary to reproduce the photoinduced midgap absorption in K-TCNQ. We find two types of midgap states. One is a usual polaronic state characterized by a localized elementary excitation. The other is superposition of two types of excitations, a doped-carrier state and a triplet-dimer state, which can be generally observed in 1D dimerized Mott insulators, not limited to K-TCNQ.View full abstractDownload PDF (177K) -
Yoshinori Okada, Tsunehiro Takeuchi, Teruhisa Baba, Shik Shin, Hiroshi ...2008 Volume 77 Issue 7 Pages 074714
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe electronic structure of Bi2Sr2−xRxCuOy (R = La, Eu) near (π,0) of the first Brillouin zone was studied by angle-resolved photoemission spectroscopy (ARPES). The temperature T* above which the pseudogap structure in the ARPES spectrum disappears was found to have an R dependence that is opposite to that of the superconducting transition temperature Tc. This indicates that the pseudogap state competes with high-Tc superconductivity, and the large suppression of Tc caused by out-of-plane disorder is due to the stabilization of the pseudogap state.View full abstractDownload PDF (187K) -
Takayuki Tajiri, Hiroyuki Deguchi, Shigemi Kohiki, Masaki Mito, Seishi ...2008 Volume 77 Issue 7 Pages 074715
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSNanocrystals of La1−xSrxMnO3+δ (0<x≤0.51) with a diameter of about 8 nm were synthesized in the pores of the mesoporous silica SBA-15. The crystal structure at all Sr concentrations had a rhombohedral symmetry. The temperature dependence of the magnetization showed ferromagnetic and superparamagnetic behavior, and the magnetization curves indicate the coexistence of a ferromagnetic and an antiferromagnetic component. ESR spectra were observed even at 77 K and were well reproduced by the summation of two absorption lines with either a Gaussian or a Lorentzian profile. The temperature dependence in the ESR spectra suggests the coexistence of two components with two transition temperatures. The magnetic phase of the nanocrystals indicates the coexistence of a ferromagnetic and an antiferromagnetic phase at all Sr concentrations studied (0<x≤0.51), with a smooth Sr dependence of the two transition temperatures. The experimental results suggest the existence of a phase separation into a ferromagnetic and an antiferromagnetic state even in nanocrystals.View full abstractDownload PDF (361K) -
Takashi Hotta2008 Volume 77 Issue 7 Pages 074716
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe discuss microscopic aspects of multipole properties of Sm-based filled skutterudite compounds under a magnetic field by analyzing a seven-orbital Anderson model with the use of a numerical renormalization group method. In order to determine the multipole state, we evaluate the susceptibility for the multipole operator defined in the form of one-body spin-charge density by the Wigner–Eckart theorem. We show our numerical results on entropy, specific heat, and multipole susceptibility of the seven-orbital Anderson model for the case of five f electrons at an impurity site under an applied magnetic field. Here we consider three directions of the magnetic field as [0,0,1], [1,1,0], and [1,1,1]. For all directions, dipoles and higher-rank multipoles with the same Γ4u symmetry are induced, but depending on the direction of the magnetic field, characteristic multipoles are found to be additionally induced. For the [1,1,1] direction, we observe that Γ2u octupole moment is induced, while for [0,0,1] and [1,1,0] directions, Γ3g quadrupole moments are found to be induced. Note that only for [0,0,1], Γ5u octupole is found to dominate dipole and Γ4u octupole. For each direction of the magnetic field, we depict a phase diagram deduced from specific heat and multipole susceptibility. Then, we discuss possible relevance of the present results with experimental ones on Sm-based filled skutterudites. Since higher-rank multipoles do not directly couple with the magnetic field, in general, the multipole Kondo effect is not so sensitive to the magnetic field, which may lead to a basic concept to understand magnetically robust heavy fermion phenomenon.View full abstractDownload PDF (257K) -
Seiichiro Suga2008 Volume 77 Issue 7 Pages 074717
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSMotivated by recent studies on the quasi-one-dimensional (1D) antiferromagnet BaCo2V2O8, we investigate the Tomonaga–Luttinger-liquid properties of the 1D S=1⁄2 XXZ Heisenberg–Ising model in magnetic fields. By using the Bethe ansatz solution, thermodynamic quantities and the divergence exponent of the NMR relaxation rate are calculated. We observe a magnetization minimum as a function of temperature (T) close to the critical field. As the magnetic field approaches the critical field, the minimum temperature asymptotically approaches the universal relation in agreement with the recent results by Maeda et al. We observe T-linear specific heat below the temperature of the magnetization minimum. The field dependence of its coefficient agrees with the results based on conformal field theory. The field dependence of the divergence exponent of the NMR relaxation rate with decreasing temperature is obtained, indicating a change in the critical properties. The results are discussed in connection with experiments on BaCo2V2O8.View full abstractDownload PDF (140K) -
Tetsuya Nakajima, Koji Hukushima2008 Volume 77 Issue 7 Pages 074718
Published: July 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe cumulant generating function φ(n) and rate function Σ(f) of free energy is evaluated in the p-body Sherrington–Kirkpatrick model by the replica method with the finite replica number n. From a perturbational argument, we show that the cumulant generating function is constant in the vicinity of n=0. On the other hand, with the help of two analytic properties of φ(n), the behavior of φ(n) is derived again. However, this is also shown to be broken at a finite value of n, which gives a characteristic value in the rate function near the thermodynamic value of the free energy. Through the continuation of φ(n) as a function of n, we find a way to derive the 1RSB solution at least in this model, which is to fix the replica symmetric (RS) solution to be a monotonically increasing function.View full abstractDownload PDF (144K)