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Volume 74, Issue 2
Displaying 1-45 of 45 articles from this issue
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Ay\\c{s}e Karasu-Kalkanli, Sergei Sakovich2005 Volume 74 Issue 2 Pages 505-507
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe (2+1)-dimensional spherical Kadomtsev–Petviashvili (SKP) equation of J.-K. Xue [Phys. Lett. A 314 (2003) 479] fails the Painlevé test for integrability at the highest resonance, where a nontrivial compatibility condition for recursion relations appears. This compatibility condition, however, is sufficiently weak and thus allows the SKP equation to possess an integrable (1+1)-dimensional reduction, which is found by the method of truncated singular expansion.View full abstractDownload PDF (61K) -
Melike Abliz, Tomohito Nakano, Echur Varadadesikan Sampathkumaran, Jea ...2005 Volume 74 Issue 2 Pages 508-510
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe intermetallic compound, CeCuAs2, crystallizing in a HfCuSi2-type tetragonal structure, has recently been shown to exhibit a negative temperature (T) coefficient of electrical resistivity (ρ) in the entire T-range of investigation (45 mK to 300 K). Here, we report that an application of external pressure (up to 10 GPa) profoundly influences ρ(T) behavior, reversing the sign of dρ⁄dT at pressures above 8 GPa, presumably arising from increasing 4f hybridization or changes in pseudo-gap. Such a behavior is uncommon among Ce-based intermetallic compounds.View full abstractDownload PDF (220K) -
Naoya Tajima, Jun-ichi Fujisawa, Nobuko Naka, Teruya Ishihara, Reizo K ...2005 Volume 74 Issue 2 Pages 511-514
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSPhoto-switching between a charge-ordered insulating (CO) state and a metallic (M) state has been successfully realized in an organic conductor α-(BEDT-TTF)2I3 at low temperatures. The large photocurrent induced by the pulsed laser excitation with a photon energy of 2.6 eV had two components. The fast-decaying component had a life time of 120 ns. The subsequent one rose slowly (after about 0.7 μs) and remained as long as an electric field above 470 V/cm was applied. The dependences of these two components on laser power, applied voltage, and the onset of pulsed voltage were examined. It has been clearly demonstrated that the second component has prominent thresholds for both laser power and voltage. For each component, the resistivity decreased by about seven orders of magnitude from about 4 MΩ·cm to less than 0.4 Ω·cm at 4 K.View full abstractDownload PDF (442K) -
Keivan Esfarjani, Amir A. Farajian, Yoshiyuki Kawazoe, Siu Tat Chui2005 Volume 74 Issue 2 Pages 515-518
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe nonlinear capacitance in doped nanotube junctions is calculated self consistently. A negative differential capacitance is observed when the applied bias becomes larger than the pseudogap of the metallic armchair nanotube. For this device, one can deduce a relaxation time of approximately 0.1 fs. Because of its negative differential resistance (NDR), a switching time of less than a femtosecond, i.e., at least three orders smaller than present-day switching times, can also be estimated. This effect is important in designing ultrafast nano-electronic components.View full abstractDownload PDF (97K) -
Toshihiro Kubo, Yasuhiro Tokura2005 Volume 74 Issue 2 Pages 519-522
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe effects of electron–electron interaction on tunneling in a semiconductor nanowhisker are studied in a magnetic quantum limit. We consider the system with which bulk and edge states coexist. In bulk states, the temperature dependence of the transmission probability is qualitatively similar to that of a one-dimensional electron system. We investigate the contributions of edge states on transmission probability in bulk states. Those contributions can be neglected within our approximation which takes into account only the most divergent terms at low temperatures.View full abstractDownload PDF (121K) -
Kikuo Harigaya2005 Volume 74 Issue 2 Pages 523-526
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSElectronic structures and optical excitations in Möbius conjugated polymers are studied theoretically. Periodic and Möbius boundary conditions are applied to the tight binding model of poly(para-phenylene), taking exciton effects into account. We discuss that oligomers with a few structural units are more effective than polymers for observations of effects of discrete wave numbers that are shifted by the change in boundary condition. Next, calculations of optical absorption spectra are reported. Certain components of optical absorption for an electric field perpendicular to the polymer axis mix with absorption spectra for an electric field parallel to the polymer axis. Therefore, the polarization dependences of an electric field of light enable us to detect whether conjugated polymers have the Möbius boundary.View full abstractDownload PDF (105K) -
Hirono Kaneyasu, Kosaku Yamada2005 Volume 74 Issue 2 Pages 527-530
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSOn the basis of a two-dimensional t–t′ Hubbard model in ferromagnetic and paramagnetic states, the triplet superconducting mechanism is investigated by the third-order perturbation theory with respect to the on-site Coulomb interaction U. In general, the superconducting state is more stable in the paramagnetic state than in the ferromagnetic state. As a special case, the dominant ferromagnetic superconductivity is obtained by the electron correlation between the electronlike majority and holelike minority bands. Furthermore, it is pointed out that in some cases the two bands play an essential role for the coexistence of superconductivity and ferromagnetism.View full abstractDownload PDF (494K) -
Minoru Kawamura, Hiroshi Yaguchi, Naoki Kikugawa, Yoshiteru Maeno, Hid ...2005 Volume 74 Issue 2 Pages 531-534
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr2RuO4–Ru. Electric contacts to individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien.View full abstractDownload PDF (232K) -
Yukio Saito, Hiroyuki Hyuga2005 Volume 74 Issue 2 Pages 535-537
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSA cluster growth model is proposed to study chiral symmetry breaking in stirred crystallization from an achiral element. Achiral monomers are assumed to coagulate to form chiral clusters from dimers to hexamers. Due to the stirring, the hexamers break into dimers. The coagulation of two dimers into a tetramer also occurs. The fixed point analysis of coupled rate equations of cluster densities and their numerical integrations show that the chiral symmetry becomes broken if dimers are critical and able to dissociate back to achiral monomers. The chirality selection is understood by showing that, in a quasi-steady approximation, the rate equations reduce to those of dimers with nonlinear autocatalysis and decomposition.View full abstractDownload PDF (97K) -
Atsunari Katsuki, Hiraku Nishimori, Noritaka Endo, Keisuke Taniguchi2005 Volume 74 Issue 2 Pages 538-541
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe collision processes of two crescentic dunes called barchans are systematically studied using a simple computer simulation model. The simulated processes, coalescence, ejection and reorganization, qualitatively correspond to those observed in a water tank experiment. Moreover we found the realized types of collision depend both on the mass ratio and on the lateral distance between barchans under initial conditions. A simple set of differential equations to describe the collision of one-dimensional (1D) dunes is introduced.View full abstractDownload PDF (211K) -
Hang-yu Ruan, Hui-jun Li2005 Volume 74 Issue 2 Pages 543-546
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe study new types solitary wave solutions of the higher order nonlinear Schrödinger equation (HONLSE) with variable coefficients, that is, the generalized higher order nonlinear Schrödinger equation (GHONLSE). The GHONLSE describes the propagation of ultrashort light pulses in optical fibers. Using the generalized Lie group reduction method (GLGRM), the abundant solitary wave solutions of GHONLSE are obtained from the known solutions of HONLSE. Some results that are applied to design of optical pulse compressor and solitary wave based communications links also have been studied.View full abstractDownload PDF (100K) -
Takasi Endo, Yutaka Hirayoshi, Kouichi Toyoshima2005 Volume 74 Issue 2 Pages 547-549
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSAn infinitely long transmission line appears to have an ohmic conductance even when loss in circuit elements approaches zero. We show that the real part of the admittance of the transmission line derives from a dense distribution of resonance absorption lines.View full abstractDownload PDF (111K) -
Toyonori Munakata, Daisuke Suzuki2005 Volume 74 Issue 2 Pages 550-553
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe rectification efficiency, recently formulated based on the Langevin equation without the overdamping approximation for the flashing ratchet model, is generalized and applied to the Feynman ratchet which is in contact with two reservoirs with different temperatures. By numerical simulations of the Langevin equation, we examine the dynamics at various temperature differences from the viewpoint of rectification efficiency and find that the direction and the mechanism of the ratchet movement is controlled by the temperature difference of the two reservoirs.View full abstractDownload PDF (96K) -
Kumi Miwa, Tetsuo Deguchi2005 Volume 74 Issue 2 Pages 554-560
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe study gelation process of chemical gels through simulation of a cluster–cluster-aggregation (CCA) model, and discuss the time development of scattering intensity I(q). With respect to the functionality of monomers, we consider two cases: the four-functional case in which all monomers have four bonds, and the mixed-functional case in which monomers with two bonds and four bonds coexist on the lattice. The structures of gels are quite different for the four-functional and mixed-functional cases. Furthermore, clusters grow faster for the four-functional case than for the mixed-functional case, with a given initial concentration investigated. However, the scattering profiles and their time evolutions are similar for the two cases. At the final stage, the peak intensity of the four-functional case is larger than that of the mixed-functional case, which should be consistent with experiments on speckle patterns.View full abstractDownload PDF (427K) -
Keiji Kosaka2005 Volume 74 Issue 2 Pages 561-567
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe local-scaling density functional theory [J. Phys. Soc. Jpn. 72 (2003) 1926; J. Phys. Soc. Jpn. 73 (2004) 882] is extended to that for systems in magnetic fields of arbitrary strength. Formally exact expressions of the exchange-correlation scalar potential and the vector one are derived. The differential virial theorem provided by Holas and March [Phys. Rev. A 56 (1997) 4595] is also obtained, whose exchange-correlation part is satisfied by the present expressions of exchange-correlation potentials. Furthermore, the integral form of the virial theorem derived by Erhard and Gross [Phys. Rev. A 53 (1996) R5] is discussed briefly, too.View full abstractDownload PDF (115K) -
Takao Wada, Toshiaki Kaneko2005 Volume 74 Issue 2 Pages 568-576
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe multiple ionization process is investigated for the molecular targets on the basis of the recently developed contracted independent electron model (CIEM), where the impact-parameter-dependent ionization probability plays a key role. We found that the multiple ionization cross sections strongly depend on the angle between the incident beam direction and the molecular axis. Also the molecular effect is found that the ionization cross section for a molecular target is not equal to the sum of those for the constituent isolated atoms. Moreover, we proved the sum rule on the net ionization cross section. Numerical estimation shows that the multiple ionization cross sections for N2 and CO molecules, bombarded by the ions at the energies of more than 100 keV/u, are in better agreement with the experimental data than the other models.View full abstractDownload PDF (326K) -
Shunji Nojima2005 Volume 74 Issue 2 Pages 577-586
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSPhotonic mode behaviors are theoretically investigated for rotating and revolving microsystems (microdisks). The present calculation clarifies the extraordinary behaviors of photonic modes, which are induced by the rotating motion of the microdisk. First, whispering gallery modes with twofold degeneracy in the microdisk at rest split off due to the onset of rotation. This rotation also excites a number of extra modes that are interpreted as being generated as those circulating in the direction opposite to the microdisk rotation. These modes reveal anticrossing and merging-regeneration phenomena in the dispersion curves of photon frequency as the rotation speed increases. The light intensity distributions in the microdisk exhibit a variety of metamorphoses according to the variations of rotation center position as well as rotation speed. All of these phenomena can be explained as being caused by the coupling of photonic modes to the rotating motion of the microdisk and the resultant coupling between different photonic states.View full abstractDownload PDF (366K) -
Numerical Simulation of Vortex Crystals and Merging in N-Point Vortex Systems with Circular BoundaryTakeshi Yoshida, Mitsusada M. Sano2005 Volume 74 Issue 2 Pages 587-598
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSIn two-dimensional (2D) inviscid incompressible flow, low background vorticity distribution accelerates intense vortices (clumps) to merge each other and to array in the symmetric pattern which is called “vortex crystals”; they are observed in the experiments on pure electron plasma and the simulations of Euler fluid. Vortex merger is thought to be a result of negative “temperature” introduced by Onsager [Nuovo Cimento 6 (1949) 279]. Slight difference in the initial distribution from this leads to “vortex crystals”. We study these phenomena by examining N-point vortex systems governed by the Hamilton equations of motion. First, we study a three-point vortex system without background distribution. It is known that a N-point vortex system with boundary exhibits chaotic behavior for N≥3. In order to investigate the properties of the phase space structure of this three-point vortex system with circular boundary, we examine the Poincaré plot of this system. Then we show that topology of the Poincaré plot of this system drastically changes when the parameters, which are concerned with the sign of “temperature”, are varied. Next, we introduce a formula for energy spectrum of a N-point vortex system with circular boundary. Further, carrying out numerical computation, we reproduce a vortex crystal and a vortex merger in a few hundred point vortices system. We confirm that the energy of vortices is transferred from the clumps to the background in the course of vortex crystallization. In the vortex merging process, we numerically calculate the energy spectrum introduced above and confirm that it behaves as k−α (α≈2.2–2.8), at the region 100<k<101 after the merging.View full abstractDownload PDF (639K) -
Ruyan Zhang, Makiko Kan, Tetuya Kawamura2005 Volume 74 Issue 2 Pages 599-604
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSTransverse dunes and linear dunes are simulated numerically in order to make clear the mechanism of the formation of two kinds of typical sand dunes. The numerical method employed in this study can be divided into three parts: (i) Calculation of the air flow above the sand dunes; (ii) Estimation of the sand transfer caused by the flow through the friction; (iii) Determination of the shape of the sand ground. Since the computational area has been changed due to the last step, these procedures are repeated until typical shapes of the sand dunes are formed. One kind of the simulated dunes, which is formed by one wind direction, becomes essentially parallel straight ridges at right angle to the wind direction with only one slip-face on the lee side, which is known as the transverse dunes; The other one, which is formed by two directional wind, becomes essentially parallel straight ridge at the converging direction with two slip-faces on both sides, which is known as linear dunes.View full abstractDownload PDF (290K) -
Kiyoyuki Yambe, Sadao Masamune, Hideki Arimoto, Koichi Sato2005 Volume 74 Issue 2 Pages 605-612
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSA plasma biasing experiment using an insertable electrode has been carried out in the STP-3(M) reversed field pinch. The profiles of electron density ne, electron temperature Te and plasma potential Vs were measured with an electrostatic probe array in the edge region of the plasma. The effect of biasing is observed as an increase of edge electron density and suppression of fluctuation amplitudes in ne, Te and Vs. As a result, both the electrostatic particle and energy fluxes are reduced and confinement improvement is observed, which is caused by the formation of E×B velocity shear layer. The reduction in both fluctuation amplitudes and coherence between fluctuating quantities contributes to this improvement. The formation of velocity shear layer is dependent on the insertion depth of the electrode, which is possibly related to the location where additional power is deposited through biasing. The extension of plasma lifetime is also observed in the biased discharges.View full abstractDownload PDF (839K) -
Ryoji Kiyanagi, Akiko Kojima, Hiroyuki Kimura, Masashi Watanabe, Yukio ...2005 Volume 74 Issue 2 Pages 613-620
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe antiferroelectric material with an isolated hydrogen-bond, h-MeHPLN (5-methyl-9-hydroxyphenalenon), was structurally investigated by X-ray and neutron diffraction experiments in the low-temperature phase (Tc=42 K). The formation of a superlattice of 2×b was found below Tc, and the space group was identified to be P21/c transformed from C2/c. Accordingly, the number of crystallographically independent molecules became two. The electron density distribution and the nuclear density distribution revealed some significant features below Tc. One of the independent molecules exhibits an ordering of the hydrogen atom in the hydrogen-bond region, a conformational ordering of the methyl group and a molecular rotation around the a-axis. Moreover, a static electronic dipole moment is found in the hydrogen-bond region in this molecule. In contrast, the other molecule shows a disordered hydrogen atom, disordered conformation of the methyl group, no molecular rotation and a disordered electronic dipole moment. These features can be described simply in terms of a modulation wave of an order parameter.View full abstractDownload PDF (481K) -
Fuyuki Shimojo, Kozo Hoshino, Y. Zempo2005 Volume 74 Issue 2 Pages 621-625
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe temperature dependences of the structural and electronic properties of liquid As2S3 are investigated by means of ab initio molecular-dynamics simulations. It is shown that the three-dimensional network structure is transformed into a two-fold chain-like structure with increasing temperature, as was seen in the liquid As2Se3. We discuss the microscopic mechanism of the charge transfer from sulfur to arsenic atoms accompanied with the semiconductor–metal transition in these liquid mixtures.View full abstractDownload PDF (234K) -
Yuuki Ono, Koichi Kusakabe, Naoshi Suzuki2005 Volume 74 Issue 2 Pages 626-630
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSMechanical properties of fullerene encapsulated nanotubes called peapods are theoretically investigated. We compared two models of the peapods in which inter-molecular forces are estimated by the ab initio calculation or by the Lennard-Jones potential. The former model concludes stiffening in every vibrational normal mode, but the latter shows softening. Although stiffness change depends on the model, we are able to extract general tendency of each specific mode. The encapsulation tends to stiffen the compressing modes and radial breathing mode (RBM), while the bending mode and the stretching mode may be softened by the encapsulation, if fullerenes and a tube attract with each other.View full abstractDownload PDF (106K) -
Masaru Sugiyama, Haruki Suzumura2005 Volume 74 Issue 2 Pages 631-637
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThermodynamic quantities of elastic solids such as elastic constants, specific heats, coefficients of thermal expansion and Grüneisen parameters are analyzed and discussed by using the linearized macroscopic basic equations proposed in the former paper of the present series. Furthermore some coefficients which relate thermal vibrations of constituent atoms to temperature variation and strain are studied. Then the Helmholtz free energy of elastic solids is formulated explicitly.View full abstractDownload PDF (154K) -
Yoshitaka Michihiro, Md. Mahbubar Rahman, Koichi Nakamura, Tatsuo Kana ...2005 Volume 74 Issue 2 Pages 638-641
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe comparative study is done on the dipole and deformation dipole polarization. With the local density approximation, the values of the dipole polarizability and the deformation dipole tensor of the ions in the rock-salt structure alkali iodide crystals are calculated. The Szigeti effective charge is obtained from the deformation dipole tensor. The crystalline potential is treated by the spherical solid model. The response to the perturbation is calculated by the self-consistent field potential. The calculated results are compared with those in other alkali halide crystals. The ease of the ionic migration is discussed by using the deformation dipole tensor.View full abstractDownload PDF (81K) -
Youhei Fujitani2005 Volume 74 Issue 2 Pages 642-647
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSA lipid-raft—a non-caveolar microdomain enriched with sphingolipids and cholesterol—is thought to be unable to grow beyond a certain size in the biomembrane in vivo. The membrane can accommodate two-dimensional flow, which could break up a larger raft. As a fundamental problem of this mechanism, a small raft-deformation in the stagnation flow is studied in this paper. The capillary number—a relevant dimensionless factor in this problem—involves viscosity of the surrounding fluids for a large enough raft, and instead that of the membrane for a small enough raft. Discussing the breakup condition of a raft, we also show that an estimate of the critical raft-size is consistent with previous observations in vivo.View full abstractDownload PDF (121K) -
Shinji Ono, Michisuke Kobayashi2005 Volume 74 Issue 2 Pages 648-652
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThe electronic states of silver halides and sodium halides are calculated by the DV-Xα cluster method to get more microscopic evidence for the p–d hybridization in noble metal halides. The calculations are carried out for the (A13B14)− (A=Ag+ and Na+, B = halogen ion) clusters. It is found that both components of anti-bonding and bonding exist in the diagram of overlap population (DOP) for AgX (X=halogen) and these two components are made up of the 4d band of Ag+ and the p band of halogen ion, which form the p–d hybridization. On the other hand, the DOP of alkali halides is occupied by almost only bonding component. It is inferred that the origin of AgI type superionic conductor is in the weakness of p–d hybridization. The hypothetical rock-salt AgI is also discussed to investigate the unstableness of rock-salt AgI.View full abstractDownload PDF (211K) -
Kozo Okada, Akio Kotani2005 Volume 74 Issue 2 Pages 653-660
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSCarrier doping effects on the Cu 2p photoemission in low-dimensional cuprates are discussed on the basis of large-cluster model calculations. The result shows that the carrier doping causes a significant change in the line shape of the main structure in the Cu 2p spectrum. It is closely related to the change in the electronic structure near the Fermi energy of the system.View full abstractDownload PDF (280K) -
Yoshihiro Shimomura, Shin Miyahara, Nobuo Furukawa2005 Volume 74 Issue 2 Pages 661-669
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe investigate a detail of a dodecamer cluster ordering in a double-exchange spin ice model on a kagomé lattice. In frustrated systems, ordinary spin orderings are suppressed and macroscopic degeneracy remains down to low temperatures. In some frustrated systems, the degeneracy is lifted due to residual interactions and cluster orderings are stabilized. In the present model, the spin ice state is first formed at intermediate temperatures, and further entropies are released at lower temperatures as the dodecamer phase emerges. Since the spin symmetry is not broken in the dodecamer phase, there still exists macroscopic degeneracy. At further low temperatures, a possible spin ordering due to inter-dodecamer interactions is proposed. We discuss that such a multiple-site clustering larger than a bond-pair might be generic to frustrated systems where macroscopic degeneracy is lifted by residual interactions.View full abstractDownload PDF (243K) -
Yukito Tanabe, Eiichi Hanamura2005 Volume 74 Issue 2 Pages 670-678
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSSymmetry of the magnons at high symmetry points of the Brillouin zone boundary in α-Fe2O3 has been determined. Selection rules for the two-magnon absorption are newly derived taking acount of the four-sublattice structure of the system. Electric dipole moment proportional to the vector product of spins is introduced and is found to be able to bring about one- and three-magnon excitation.View full abstractDownload PDF (168K) -
Syuma Yasuzuka, Shinya Uji, Hiroshi M. Yamamoto, Jun-Ichi Yamaura, Chi ...2005 Volume 74 Issue 2 Pages 679-685
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSThis paper reports the measurements of Shubnikov–de Haas (SdH) and angular-dependent magnetoresistance oscillations (AMROs) for new layered organic conductors ET3Cl(DFBIB) and ET3Br(pBIB), where ET, DFBIB, and pBIB stand for bis(ethylenedithio)tetrathiafulvalene, 1,4-difluoro-2,5-bis(iodoethynyl)benzene, and p-bis(iodoethynl)benzene, respectively. Each of them has only a two-dimensional Fermi surface (FS), whose cross sectional area corresponds to about 50% of the first Brillouin zone. No significant difference between them is found in the size and shape of the cross-section of the FS. In spite of the similarity of the electronic state, the sharp peaks in the magnetoresistance are clearly observed for ET3Cl(DFBIB) under in-plane magnetic fields, while anomalous broad peaks for ET3Br(pBIB). The results suggest that the anion structure play an important role in the interlayer transport.View full abstractDownload PDF (450K) -
Nobuhiro Kusuno, Tohru Kawamoto, Koichi Kusakabe, Naoshi Suzuki2005 Volume 74 Issue 2 Pages 686-689
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSTo determine efficient molecular junction configurations for use in switches, we analyzed the conductance of a model representing a molecular junction with a ring-shaped molecule weakly connected with two one-dimensional electrodes, taking into account resonance and interference effects. We considered a model in which the center molecule changes in shape from a ring to a chain and the Fermi energy lies at the center of the molecular eigenstates. We discovered that requirements for switching, which include particular atomic contacts relative to the reaction site, single out the following two cases as the most effective junctions. The large conductance through a 4m-membered ring due to the resonance effect becomes small when the conduction path becomes a chain. A less-conductive 4m+2-membered ring in the off-resonance state is switched on by the resonance effect in the final chain-shaped path.View full abstractDownload PDF (95K) -
David M.-T. Kuo, Yia-Chung Chang2005 Volume 74 Issue 2 Pages 690-699
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe present theoretical studies on the spontaneous emission spectrum of a single self-assembled InAs/GaAs quantum dot (SAQD) embedded in a p–n junction under bias via Keldysh’s non-equilibrium Green’s function method. For this open system, the emission spectrum can display four coexisting peaks, corresponding to the recombination of exciton, positive and negative trions, and biexciton, even though there is only a single quantum dot. The integrated intensities of the exciton and biexciton peaks increase, respectively, linearly and quadratically with tunnelling rates.View full abstractDownload PDF (224K) -
Kenji Kawashima, Akihiko Kawano, Takahiro Muranaka, Jun Akimitsu2005 Volume 74 Issue 2 Pages 700-704
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe discovered superconductivity in W7Re13X (X=B and C) (Tc=7.1 K and 7.3 K, respectively), and their superconducting properties are discussed. The crystal structure of W7Re13X is β-Mn-type (cubic, space group: P4132), and Re atoms form a tilted octahedron. The magnetization (M–H) curves show typical type-II superconducting behavior, and the lower critical field Hc1(0), the upper critical field Hc2(0) and the Ginzburg–Landau (GL) parameter κ are 7.7 mT, 11.4 T and 54 for X=B and 4.0 mT, 12.6 T and 80 for X=C, respectively. From the specific heat measurement, the superconducting gap magnitudes are estimated to be 2Δ⁄kBTc=4.28 and 4.02, respectively.View full abstractDownload PDF (563K) -
H. Kotegawa, A. Harada, S. Kawasaki, Y. Kawasaki, Y. Kitaoka, Y. Haga, ...2005 Volume 74 Issue 2 Pages 705-711
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe report on the itinerant ferromagnetic superconductor UGe2 through 73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum signals a first-order transition from the low-temperature (T) and low-P ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical pressure of Px∼1.2 GPa. The superconductivity exhibiting a maximum value of Tsc=0.7 K at Px∼1.2 GPa, was found to take place in connection with the P-induced first-order transition. The nuclear spin–lattice relaxation rate 1⁄T1 has probed the ferromagnetic transition, exhibiting a peak at the Curie temperature as well as a decrease without the coherence peak below Tsc. These results reveal the uniformly coexistent phase of ferromagnetism and unconventional superconductivity with a line–node gap. We remark on an intimate interplay between the onset of superconductivity and the underlying electronic state for the ferromagnetic phases.View full abstractDownload PDF (739K) -
Hiromasa Yoshimura, Dai S. Hirashima2005 Volume 74 Issue 2 Pages 712-721
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSMagnetic and superconducting properties of electron-doped high-temperature superconductors are studied with fluctuation exchange approximation applied to the Hubbard model on a square lattice. In contrast to hole-doped cases, the hot spots, the intersections of the magnetic Brillouin zone boundary and the Fermi surface, are located near the diagonals of the Brillouin zone. This is found to result in (1) a weaker coupling between the antiferromagnetic spin fluctuations and quasiparticles and (2) a peculiar deviation of the angular dependence of the order parameter from a simple form of coskxa−coskya. The latter is consistent with the implication from Raman scattering experiments, and can be direct evidence of superconductivity caused by antiferromagnetic spin fluctuations.View full abstractDownload PDF (271K) -
Yuki Fuseya, Hiroshi Kohno, Kazumasa Miyake2005 Volume 74 Issue 2 Pages 722-730
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSA mechanism of the quasi-one-dimensional (q1d) superconductivity is investigated by applying the renormalization group techniques to the pairing interaction. With the renormalized pairing interaction, the transition temperature Tc and corresponding gap function are calculated by solving the linearized gap equation. For reasonable sets of parameters, Tc of p-wave triplet pairing is higher than that of d-wave singlet pairing due to the one-dimensionality of interaction. These results can qualitatively explain the superconducting properties of q1d organic conductor (TMTSF)2PF6 and the ladder compound Sr2Ca12Cu24O41.View full abstractDownload PDF (248K) -
Kenji Ohoyama, Kentaro Indoh, Aya Tobo, Koji Kaneko, Aya Hino, Hideya ...2005 Volume 74 Issue 2 Pages 731-734
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSDetailed neutron diffraction measurements were performed on a single crystalline sample of Er11B2C2. We observed magnetic diffuse scattering, which consists of three components, just above the transition temperatures. This scattering is also observed in anomalous antiferroquadrupolar ordering compounds,TbB2C2 and HoB2C2. The results of the experiments indicate that the antiferroquadrupolar interaction is not essential for the origin of the magnetic diffuse scattering.View full abstractDownload PDF (138K) -
Osamu Suzuki, Shintaro Nakamura, Mitsuhiro Akatsu, Yuichi Nemoto, Teru ...2005 Volume 74 Issue 2 Pages 735-741
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe have investigated the elastic properties of the cubic dense Kondo compound Ce0.75La0.25B6 by means of ultrasonic measurements. We have obtained magnetic fields vs temperatures (H–T) phase diagrams under magnetic fields along the crystallographic [001], [110] and [111] axes. An ordered phase IV showing the elastic softening of c44 locates in low temperature region between 1.6 and 1.1 K below 0.7 T in all field directions. The phase IV shows an isotropic nature with regard to the field directions, while the antiferro-magnetic phase III shows an anisotropic character. A remarkable softening of c44 and a spontaneous trigonal distortion εyz+εzx+εxy recently reported by Akatsu et al. [J. Phys. Soc. Jpn. 72 (2003) 205] in the phase IV favor a ferro-quadrupole (FQ) moment of Oyz+Ozx+Oxy induced by an octupole ordering.View full abstractDownload PDF (227K) -
Md. Mahmudur Rahman, Masanori Kisaku, Tomoya Kishi, Tanglaw Abat Roman ...2005 Volume 74 Issue 2 Pages 742-745
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe investigate the electric and magnetic properties of a (3,3) single-walled carbon nanotube filled with a linear Co nanowire. We carry out first-principle calculations based on the spin-polarized density functional theory, and find that in the stable structure, it shows half metallic ferromagnetic behavior, i.e., the majority-spin electrons show metallic behavior while the minority-spin electrons have a semiconducting bandgap.View full abstractDownload PDF (220K) -
C. Stock, S. Wakimoto, R. J. Birgeneau, S. Danilkin, J. Klenke, P. Sme ...2005 Volume 74 Issue 2 Pages 746-752
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe present neutron elastic scattering results at high magnetic fields for Mg-doped CuGeO3. For low magnesium concentrations, where a spin-Peierls phase is present, we find an enhancement of the long range antiferromagnetic order in the structural incommensurate phase induced by a high magnetic field. In the incommensurate phase, the Néel temperature increases with field leading to a gain in the magnetic Bragg peak intensity at low temperatures. We also find that the magnetic Bragg peaks remain commensurate even though the structure is incommensurate at high magnetic fields due to the formation of solitons. We interpret these results in terms of the solitons formed at high-magnetic fields effectively acting as doped impurities. Our results point to a strongly disordered ground state with the antiferromagnetic order localized around impurity sites.View full abstractDownload PDF (353K) -
Kotaro Ishiji, Hironori Yamasaki, Takahito Masui, Hiroo Hashizume2005 Volume 74 Issue 2 Pages 753-757
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSMagnetic polarizations of delocalized electrons in spacer layers are detected in exchange-coupled Co/CuNi multilayers by a measurement of X-ray magnetic circular dichroic absorptions. The size of the Cu K-edge dichroism shows a variation closely related to the oscillatory exchange coupling as a function of the spacer CuNi thickness. The magnetic polarization of the CuNi 4p electrons is locally minimal at the spacer thickness where the magnetoresistance reaches a local maximum, indicating that the integrated local spin density in the spacer layer oscillates with the spacer thickness with the same period as, but in 180° phase with, the indirect coupling of the Co moments across the CuNi layer.View full abstractDownload PDF (229K) -
Satoshi Miyashita, Norio Kawakami2005 Volume 74 Issue 2 Pages 758-764
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSWe investigate ground-state properties of a one-dimensional S=1 spin–orbital model with or without uniaxial single-ion anisotropy. By means of the density matrix renormalization group method, we compute the ground-state energy, the magnetization curves and the correlation functions. We discuss how the ground-state properties depend on the two exchange couplings for orbital and spin sectors. The phase diagramobtained is compared with that for the S=1⁄2 model. We also address the effect of uniaxial single-ion anisotropy.View full abstractDownload PDF (191K) -
Tatsuya Nagao, Jun-ichi Igarashi2005 Volume 74 Issue 2 Pages 765-772
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSBased on a localized crystal electric field model for the U4+ in the (5f)2-configuration, we analyze the resonant x-ray scattering spectra around U MIV and MV edges in URu2Si2, taking full Coulomb and spin–orbit interactions into account. We consider two level schemes, a singlet model of Santini and Amoretti and a doublet model of Ohkawa and Shimizu [J. Phys.: Condens. Matter 11 (1999) L519], and assume the antiferroquadrupolar (AFQ) order and the antiferrooctupolar (AFO) order as candidates for the ambient pressure phase as well as the antiferromagnetic (AFM) order as that for the high pressure phase. It is found that the spectral shapes as a function of photon energy are independent of the assumed level scheme, but are quite different between the AFQ and AFM phases, while the AFO phase shows no scattering intensity. This may be useful to determine the character of the ordered phase.View full abstractDownload PDF (171K) -
R. A. Clemente, A. M. Saleh2005 Volume 74 Issue 2 Pages 773-775
Published: February 15, 2005
Released on J-STAGE: November 20, 2007
JOURNAL RESTRICTED ACCESSA simple phenomenological model for the crystallization kinetic of two step phase transformations is proposed. The treatment assumes that an amorphous or undercooled liquid material begins to transform into a transient metastable phase which starts to grow, at the same time the final phase starts to grow inside the metastable one, consuming it but without exceeding it. The starting material and the different phases are all assumed of the same chemical composition and the transformation processes are assumed interface controlled. As a result the starting material completely transforms to the final phase and no trace of the transient one will remain. The model properly take into acount the impingement of growing grains and can be applied to a number of transformations like solidification of undercooled liquid metallic alloys and divritification of glasses and amorphous solids.View full abstractDownload PDF (69K)
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