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Volume 75, Issue 8
Displaying 1-50 of 50 articles from this issue
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Yoshitaka Tanimura2006 Volume 75 Issue 8 Pages 082001
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSHalf century has past since the pioneering works of Anderson and Kubo on the stochastic theory of spectral line shape were published in J. Phys. Soc. Jpn. 9 (1954) 316 and 935, respectively. In this review, we give an overview and extension of the stochastic Liouville equation focusing on its theoretical background and applications to help further the development of their works. With the aid of path integral formalism, we derive the stochastic Liouville equation for density matrices of a system. We then cast the equation into the hierarchy of equations which can be solved analytically or computationally in a nonperturbative manner including the effect of a colored noise. We elucidate the applications of the stochastic theory from the unified theoretical basis to analyze the dynamics of a system as probed by experiments. We illustrate this as a review of several experimental examples including NMR, dielectric relaxation, Mössbauer spectroscopy, neutron scattering, and linear and nonlinear laser spectroscopies. Following the summary of the advantage and limitation of the stochastic theory, we then derive a quantum Fokker–Planck equation and a quantum master equation from a system–bath Hamiltonian with a suitable spectral distribution producing a nearly Markovian random perturbation. By introducing auxiliary parameters that play a role as stochastic variables in an expression for reduced density matrix, we obtain the stochastic Liouville equation including temperature correction terms. The auxiliary parameters may also be interpreted as a random noise that allows us to derive a quantum Langevin equation for non-Markovian noise at any temperature. The results afford a basis for clarifying the relationship between the stochastic and dynamical approaches. Analytical as well as numerical calculations are given as examples and discussed.View full abstractDownload PDF (6260K) -
Naoki Kobayashi, Kaoru Kohyama, Yo Sasaki, Mitsugu Matsushita2006 Volume 75 Issue 8 Pages 083001
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSFragment-size distribution has been studied experimentally by masticating raw carrot. For a few chews a single lognormal distribution well fits the entire region for masticated food fragments. Furthermore, the fragment-size distribution changes from a single lognormal structure to a double-size-group structure of lognormal with a power-law tail as the number of chews increases. The most of the fragments belong to the smaller size region characterized by the lognormal distribution, whereas the larger size region showed a power-law distribution. The excellent data fitting by the lognormal and power-law distributions implies that two functions of mastication, a sequential fragmentation with cascade and randomness, and a lower threshold for fragment size, affect the size distribution of masticated food fragments.View full abstractDownload PDF (165K) -
Takeshi Ogasawara, Sadayoshi Toh2006 Volume 75 Issue 8 Pages 083401
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSTurbulent relative dispersion is theoretically studied using the probability distribution function (PDF) of the relative separation of two passive particles in the inertial range of homogeneous, isotropic, and stationary turbulence. Taking into account a finite separation speed and finite correlation of relative velocity by multiple-scale consideration, a telegraph equation with scale-dependent coefficients, which has a similarity solution, is derived. The tail of the solution falls off to zero at a maximum separation due to the finite separation speed. For slowly separating particle pairs, the equation is approximated by Richardson’s diffusion equation with a drift term. The drift term plays an important role in the description of the main part of the separation PDF and tail part of the exit-time PDF. The relationship between the drift term and coherent structures is discussed for two 2D turbulence cases.View full abstractDownload PDF (179K) -
Hirokazu Tsunetsugu, Mitsuhiro Arikawa2006 Volume 75 Issue 8 Pages 083701
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSSpin nematic order is investigated for an S=1 spin model on a triangular lattice with bilinear–biquadratic interactions. We particularly studied an antiferro nematic order phase with a three-sublattice structure, and magnetic properties are calculated at zero temperature by bosonization. Two types of bosonic excitations are found and we calculated dynamic and static spin correlations. One is a gapless excitation with linear energy dispersion around k∼0, and this leads to a finite spin susceptibility at T=0 and would have a specific heat C(T)∼T2 at low temperatures. These behaviors can explain many of the characteristic features of a recently discovered spin liquid state in the triangular magnet, NiGa2S4.View full abstractDownload PDF (325K) -
Katsunori Kubo, Takashi Hotta2006 Volume 75 Issue 8 Pages 083702
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe propose a concept of superconductivity controlled by orbital degree of freedom taking CeMIn5 (M=Co, Rh, and Ir) as typical examples. A microscopic multiorbital model for CeMIn5 is analyzed by fluctuation exchange approximation. Even though the Fermi-surface structure is unchanged, the ground state is found to change significantly among paramagnetic, antiferromagnetic, and d-wave superconducting phases, depending on the dominant orbital component in the band near the Fermi energy. We show that our picture naturally explains the different low-temperature properties of CeMIn5 by carefully analyzing the crystalline electric field states.View full abstractDownload PDF (142K) -
Takahiro Yabuuchi, Takahiro Matsuoka, Yuki Nakamoto, Katsuya Shimizu2006 Volume 75 Issue 8 Pages 083703
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe pressure dependence of the superconducting transition temperature Tc in calcium was measured up to 161 GPa. Tc increased significantly with pressure and reached 25 K at 161 GPa, which is the highest observed Tc for all elements. Compared with the result obtained in a recent structural experiment, Tc increases within the simple cubic structure phase and becomes rather stable but still increases in the Ca-IV and Ca-V phases.View full abstractDownload PDF (321K) -
Satoshi Fujimoto2006 Volume 75 Issue 8 Pages 083704
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe argue the emergence of nodal excitations due to coupling with static antiferromagnetic order in fully gapped superconducting states in both cases with and without inversion symmetry. This line node structure is not accompanied by a sign change of the superconducting gap, in contrast to that of usual unconventional Cooper pairs with higher angular momenta. In the case without inversion symmetry, the stability of the nodal excitations crucially depends on the direction of the antiferromagnetic staggered magnetic moment. A possible realization of this phenomenon in CePt3Si is discussed.View full abstractDownload PDF (382K) -
Takahiro Misawa, Youhei Yamaji, Masatoshi Imada2006 Volume 75 Issue 8 Pages 083705
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSDivergent carrier-density fluctuations equivalent to the critical opalescence of gas–liquid transition emerge around a metal–insulator critical point at a finite temperature. In contrast to the gas–liquid transitions, however, the critical temperatures can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau, and Wilson is violated because of its topological nature. It offers a clear insight into the criticalities of metal–insulator transitions (MIT) associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order MIT and must shed new light on remarkable phenomena found in correlated metals such as unconventional cuprate superconductors. It indeed accounts for the otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to accurately measure enhanced dielectric fluctuations at small wave numbers.View full abstractDownload PDF (121K) -
S. Akbar Jafari, Takami Tohyama, Sadamichi Maekawa2006 Volume 75 Issue 8 Pages 083706
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe formulate the third harmonic generation (THG) within the dynamical mean field theory (DMFT) approximation of the Hubbard model. In the limit of large dimensions, where DMFT becomes exact, the vertex corrections to current vertices are identically zero. Hence, the calculation of the THG spectrum reduces to a time-ordered convolution, followed by an appropriate analytic continuation. We present a typical THG spectrum of the Hubbard model obtained by this method. Within our DMFT calculation, we observe a nontrivial approximate scaling function describing the THG spectra in all Mott insulators, independent of the gap magnitude.View full abstractDownload PDF (116K) -
Takeshi Ogasawara, Kenya Ohgushi, Hiroshi Okamoto, Yoshinori Tokura2006 Volume 75 Issue 8 Pages 083707
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe photoinduced dynamics of sublattice magnetization in ferrimagnetic compounds, FeCr2S4 and CoCr2S4, was investigated by time-resolved magneto-optical Kerr spectroscopy probing element-specific optical transitions. In FeCr2S4, the non-collinear dynamics of the sublattice magnetizations was observed. Upon irradiation of a 200 fs laser pulse, the Cr sublattice magnetization starts to precess, whereas the Fe sublattice magnetization starts to decrease without precession. In CoCr2S4, by contrast, Co and Cr sublattice moments show the same precession, retaining the collinear relation after photoexcitation. The versatile collinear/noncollinear spin dynamics can be accounted for in terms of the relative magnitude of the magnetocrystalline anisotropy at the Fe/Co site to the exchange interaction between Cr and Fe/Co spins.View full abstractDownload PDF (180K) -
Tadashi Machida, Yusuke Kamijo, Keiji Harada, Tetsurou Noguchi, Ryo Sa ...2006 Volume 75 Issue 8 Pages 083708
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe spatial variation of the local density of states in optimally doped Bi2Sr1.6La0.4CuO6+δ (superconducting transition temperature is 34 K) is studied by scanning tunneling spectroscopy at 4.2 K in zero magnetic field. Two-dimensional density-of-states modulation aligned with the Cu–O–Cu bond with a periodicity of about five lattice constants is observed. It is found that this modulation accompanies the appearance of a new energy gap of approximately 10 meV, whose gap edge peak is spatially modulated in intensity. This gap coexists with the superconducting gap, the value of which ranges from 10 meV to 60 meV.View full abstractDownload PDF (568K) -
Kumiko Morimoto, Yutaka Itoh, Kazuyoshi Yoshimura, Masaki Kato, Ken Hi ...2006 Volume 75 Issue 8 Pages 083709
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe report the magnetic susceptibility and NMR studies of a spin-gapped layered compound Na2Cu2TeO6 (the spin gap Δ∼250 K), the hole doping effect on the Cu2TeO6 plane via a topochemical Na deficiency by soft chemical treatment, and the static spin vacancy effect by nonmagnetic impurity Zn substitution for Cu. A finite Knight shift at the 125Te site was observed for pure Na2Cu2TeO6. The negative hyperfine coupling constant 125Atr is an evidence for the existence of a superexchange pathway of the Cu–O–Te–O–Cu bond. It turned out that both the Na deficiency and Zn impurities induce a Curie-type magnetism in the uniform spin susceptibility in an external magnetic field of 1 T, but only the Zn impurities enhance the low-temperature 23Na nuclear spin-lattice relaxation rate whereas the Na deficiency suppresses it. A spin glass behavior was observed for the Na-deficient samples but not for the Zn-substituted samples. The dynamics of the unpaired moments of the doped holes are different from that of the spin vacancy in the spin-gapped Cu2TeO6 planes.View full abstractDownload PDF (279K) -
Syuma Yasuzuka, Kensuke Kobayashi, Hiroyuki Nishikawa, Harukazu Yoshin ...2006 Volume 75 Issue 8 Pages 083710
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe temperature–pressure (T–P) phase diagram of the reduced π-donor system (MeDH-TTP)2AsF6 is studied using resistivity measurement, where MeDH-TTP stands for 2-methyl-5-(1,3-dithiolan-2-yliden)-1,3,4,6-tetrathiapentalene. The insulating phase is suppressed completely beyond Pc=2.4 GPa. Above Pc, we find two distinct metallic states that are regarded as the Fermi liquid (FL) state at lower temperatures and the “bad metal” at higher temperatures. Around Pc, remarkable enhancements in the residual resistivity ρ0 as well as in the T2-term coefficient A associated with FL behavior are found. We discuss the origin of the insulating phase and the possible quantum critical point at Pc in (MeDH-TTP)2AsF6.View full abstractDownload PDF (547K) -
Dong-Uk Cho, Yusril Yusuf, Shigehiro Hashimoto, P. E. Cladis, Helmut R ...2006 Volume 75 Issue 8 Pages 083711
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe electrooptical effects of polydomain liquid crystal elastomers (LCEs) swollen with low molecular weight liquid crystals (LMWLCs) have been investigated in detail. A well known LMWLC, 4-n-pentyl-4-cyanobiphenyl (5CB), is used as the solvent. The optical intensity of transmittance was measured as a function of voltage. The switching behavior was characterized by the voltage and time dependences of the transmittance on an instantaneous voltage switch. It is found that the threshold for the onset of the electrooptical effects is small (V∼1.0 V). The measured response time when switching on for the electrooptical effects is consistent with the response behavior of ordinary liquid crystals. However, the relaxation time when switching off shows a voltage independence and its value is about 4 times smaller than that of the electromechanical effect.View full abstractDownload PDF (189K) -
Kiyoshi Sogo2006 Volume 75 Issue 8 Pages 084001
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSExplicit formulas for several discrete integrable maps with periodic boundary condition are obtained, which give the sequential time developments in a form of the quotient of successive determinants of tri-diagonal matrices. We can expect that such formulas make the corresponding numerical simulations simple and stable. The cases of discrete Lotka–Volterra and discrete KdV equations are demonstrated by using the common algorithm computing determinants of tri-diagonal matrices.View full abstractDownload PDF (93K) -
Noboru Hashimoto2006 Volume 75 Issue 8 Pages 084002
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe author proposes a stochastic model system, that consists of a finite number of elements and shows “critical behaviors” for a certain range of the system parameter. The constituent elements are assumed to interact with each other in a mean-field way. It is shown that the temporal evolution of the order parameter of the system becomes a random multiplicative process, when the system is in the “critical state”. As a result, the state variables display large fluctuations whose statistical natures are characterized by power-laws. We consider that the present model provides a possible explanation for the ubiquitousness of power-laws in the world.View full abstractDownload PDF (144K) -
Masato Inoue, Koji Hukushima, Masato Okada2006 Volume 75 Issue 8 Pages 084003
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe replica method (RM) provides an accurate evaluation of a class of mean-field (MF) models in the thermodynamic limit. It is, however, not straightforward to extend its application to a class of non-MF models and finite-size models with sufficient accuracy. We previously proposed a numerical approach as an alternative, in which principal component analysis (PCA) is employed to analyze configurations sampled through Monte Carlo simulations. Using this method, we examine both two- and three-body mean-field Sourlas codes as a test board and compare our results with those of the RM. We confirm that the spin distribution map constructed using PCA axes has specific characteristics approximately corresponding to the phases given by RM. This result suggests that the PCA approach will be effective even with general non-MF finite-size models.View full abstractDownload PDF (318K) -
Norio Inui2006 Volume 75 Issue 8 Pages 084004
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe magnitude of the Casimir force between macroscopic dielectric bodies depends on the dielectric functions. In particular, the Casimir force between two parallel plates whose dielectric function can be described by the Drude model interacts more strongly as the plasma frequency near the surfaces separated with a small gap increases. If the plasma frequency is proportional to the number of electrons, the Casimir energy is decreased by concentrating electrons on the surface. We compare the reduction in the Casimir energy with the increment in the energy of the electric field resulting from polarization. Further, we consider a possibility that the distribution of electrons in a pair of dielectric plates spontaneously changes because of the Casimir effect.View full abstractDownload PDF (146K) -
Aki-Hiro Sato, Junpei Oshiro2006 Volume 75 Issue 8 Pages 084005
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSRecent accumulation of high frequency financial data due to development of information technology allows us to analyze behaviors of market participants in high resolution. In this article, we focus on tick frequency obtained from the high frequency data and investigate the characteristics of the tick frequency by utilizing spectrograms. Moreover the method to quantify the similarity between currency pairs based on the Kullback–Leibler divergence between spectrograms of the tick frequency for two currency pairs is proposed, and the time series of the similarities between currency pairs are computed. It is found that the recent markets are more similar than the past markets from the viewpoint of the tick frequency.View full abstractDownload PDF (770K) -
Muneki Yasuda, Kazuyuki Tanaka2006 Volume 75 Issue 8 Pages 084006
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe expand some approximate free energies in the cluster variation method for random Ising models with respect to exchange interactions, and compare them with the Plefka’s expansion. It can be clarified that some approximate free energies in the cluster variation method include all terms relating to specific clusters (or diagrams) in Plefka’s expansion. Revealing the relationship between Plefka’s expansion and the cluster variation method allows us to understand how the cluster variation method treats correlations among nodes.View full abstractDownload PDF (158K) -
Seiji Miyoshi, Tatsuya Uezu, Masato Okada2006 Volume 75 Issue 8 Pages 084007
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSConventional ensemble learning combines students in the space domain. On the other hand, in this paper, we combine students in the time domain and call it time-domain ensemble learning. We analyze the generalization performance of time-domain ensemble learning in the framework of on-line learning using a statistical mechanical method. We use a model in which both the teacher and the student are linear perceptrons with noises. Time-domain ensemble learning is twice as effective as conventional space-domain ensemble learning.View full abstractDownload PDF (172K) -
Shouzou Sugitani, Kuniaki Nagayama2006 Volume 75 Issue 8 Pages 084401
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSA transmission electron microscopic (TEM) scheme to reconstitute wavefronts of electrons scattered from objects, which was termed as complex observation (COBS), has been successfully introduced. COBS is based on a complex combination of two orthogonal TEM experiments of the conventional (bright-field) and Zernike phase contrast method, both of which are relying on the interference phenomenon for the phase recovery. Recently, another class of phase recovery, the non-interference method often called as the Transport of Intensity Equation (TIE) method, has been proposed. TIE rather relies on the change of the optical energy or intensity in the direction of wave transfer. We report the methodological comparison between COBS and TIE, which has been carried out with TEM simulations and by using a new index, ITR, which was introduced in a previous paper for the comparison of principal aspects of microscopic schemes. TEM simulation has been clarified the preference of COBS in the image quality. This has been also confirmed quantitatively by using ITR, where the drawback of TIE comes to more visible. TIE inherently requests a differential operation to close the formulation, which is actually problematic for images including noise components. Signals in the low and high frequency regions are both seriously influenced by the noise, which results in a rather low resolution image for objects with a low dose limit such as biological samples.View full abstractDownload PDF (563K) -
Thant Sin Naing, Toshiaki Kobayashi, Yoshihiko Kobayashi, Masaru Suzuk ...2006 Volume 75 Issue 8 Pages 084601
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe sound velocity propagating along [111] of LaCoO3 has been measured from 4 to 580 K for longitudinal (L) and transverse (T) sounds with frequencies, f, of 10 to 100 MHz. A comparison of the data for the single-domain rhombohedral crystal with those for a twinned pseudocubic specimen reveals the anisotropy of the elastic constants with the rhombohedral symmetry. The temperature dependence of the velocity of the L mode with f=10 MHz is analyzed consistently with the anomalous lattice expansion associated with the spin state transition. A frequency dispersion of the sound velocity appears in the L mode above 100 K. The amplitude of the dispersion increases pronouncedly with increasing temperature up to the measured highest temperature. The relaxation rate of the lattice evaluated based on the Debye model shows an activation type of temperature dependence with an attempt frequency of (1⁄τ)0=187×106 s−1 and the energy Ea=11 meV. The slow lattice relaxation is attributed to a fluctuation of the orbital-order of Co atoms in the intermediate spin state and also to the relaxation between the intermediate- and the high-spin states, the rate of which is slowed down to that of the orbital fluctuation.View full abstractDownload PDF (317K) -
Akihiko Matsuyama2006 Volume 75 Issue 8 Pages 084602
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSA van der Waals model is introduced to describe liquid–bcc–fcc phase transitions and phase separations, including unstable and metastable regions. We introduce translational order parameters, or degree of a crystalline ordering, for bcc and fcc structures. Combining a van der Waals theory for an imperfect gas with these translational order parameters, we derive the free energy, which is given by one conserved order parameter (concentration) and nonconserved order parameters (degree of a crystalline order). We calculate the phase diagrams on the temperature–concentration plane and find bcc and fcc unstable regions, a bcc–fcc phase separation, and a liquid–bcc–fcc triple point. We also calculate temporal evolution of structure factors for concentration and for crystalline order, depending on a quench temperature and concentration and find a new spinodal decomposition, driven by the instability of a fcc ordering.View full abstractDownload PDF (184K) -
Su-Hui Liang, Jia-Hao Li, Bai-Xin Liu2006 Volume 75 Issue 8 Pages 084603
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSAn n-body potential of the Ni–Sc system is constructed under tight-binding formalism and the constructed potential is capable of reproducing some static and dynamic properties of the system. Applying the proven relevant Ni–Sc potential, molecular dynamics simulations are carried out using the solid solution and sandwich models. Simulations using the solid solution models not only reproduce the experimentally observed crystal-to-amorphous transition in the system, but also clarify that the physical origin of the transition is the crystalline lattice collapsing when the solute atoms are exceeding the critical solid solubilities. The critical solid solubilities are determined to be 18±2% Ni in the hcp Sc-based solid solutions and 20±2% Sc in fcc Ni-based solid solutions, which follows that the intrinsic glass-forming ability of the Ni–Sc system is within about 18–80% Ni, matching well with that observed in ion beam mixing experiments. Result of simulations using the Ni/Sc/Ni sandwich models indicate that the Ni–Sc amorphous layer at the interfaces grows in a layer-by-layer mode and the growth speeds towards the Ni and Sc lattices are approximately the same.View full abstractDownload PDF (1494K) -
Fumihiro Ishikawa, Keiichi Koyama, Kazuo Watanabe, Tetsuya Asano, Hiro ...2006 Volume 75 Issue 8 Pages 084604
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSStructural transformations of MnAs and MnAs0.9Sb0.1 were investigated by X-ray diffraction in high magnetic fields up to 5 T. The temperature dependence of the magnetization was measured in a magnetic field of 0.01 T and the Curie temperature TC was determined to be 315 K for MnAs and 290 K for MnAs0.9Sb0.1 during heating process. For both compounds, a metamagnetic transition from a paramagnetic to a ferromagnetic state was observed above TC. The X-ray diffraction profile at 319 K for MnAs showed a single phase of an orthorhombic MnP-type structure in zero field. An applied magnetic field of 3 T induced the appearance of a hexagonal NiAs-type structure. On further increase of the magnetic field, a single phase with a hexagonal structure was realized above 3.5 T in a forced-ferromagnetic state. The X-ray diffraction profile at 295 K for MnAs0.9Sb0.1 showed a hexagonal NiAs-type structure. The coexistence of ferromagnetic and paramagnetic states with different lattice parameters was confirmed in a magnetic field of 2.5 T. The volume expansion induced by a magnetic field was found to be 2.1% for MnAs and 1.1% for MnAs0.9Sb0.1.View full abstractDownload PDF (253K) -
Yoshinori Ohmasa, Shin Takahashi, Kensuke Fujii, Yota Nishikawa, Makot ...2006 Volume 75 Issue 8 Pages 084605
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe have studied the wetting dynamics of liquid Se–Tl mixtures on a silica wall experimentally. When the temperature drop is given to the system, a Se-rich wetting film is formed transiently between the Tl-rich phase and the silica wall even under the non-wetting condition. The complete wetting persists for a while, and then the wetting film disappears eventually. In the dewetting process, inhomogeneous patterns of the wetting film are observed, and the fraction of the area of the dry-patches increases with time t as tα (α\\simeq1.5).View full abstractDownload PDF (166K) -
Kuiwei Geng, Fei Zeng, Yu Gu, Cheng Song, Xiaoxue Wei, Feng Pan2006 Volume 75 Issue 8 Pages 084701
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSFe/Ho multilayers were prepared by electron-beam evaporation. A vector vibrating sample magnetometer is adopted to investigate the multilayers in-plane and out-plane magnetic properties, and an inverted hysteresis loop is obtained in the direction perpendicular to the applied magnetic field. The loop shape is sensitive to the angle between the film plane and the direction of magnetic field. A proposal module is used to explain this mechanism. The results of magnetoresistance measurement show that the multilayers have a positive magnetoresistance. The Fe layer thickness has a marked effect on the electronic resistance and magnetoresistance properties of the Fe/Ho multilayers.View full abstractDownload PDF (221K) -
Kota Hanasaki, Masatoshi Imada2006 Volume 75 Issue 8 Pages 084702
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSFilling-control metal–insulator transition on the two-dimensional Hubbard model is investigated by using the correlator projection method, which takes into account the momentum dependence of the free energy beyond the dynamical mean-field theory. The phase diagram of metals and Mott insulators is analyzed. Lifshitz transitions occur simultaneously with metal–insulator transitions for large Coulomb repulsion. On the other hand, they are separated each other for smaller Coulomb repulsion, where the phase sandwiched by the Lifshitz and metal–insulator transitions appears to show violation of the Luttinger sum rule. Through the metal–insulator transition, quasiparticles retain nonzero renormalization factor and finite quasi-particle weight on both sides of the transition. This supports that the metal–insulator transition is caused not by the vanishing renormalization factor but by the relative shift of the Fermi level into the Mott gap away from the quasiparticle band, in sharp contrast with the original dynamical mean-field theory. Charge compressibility diverges at the critical end point of the first-order Lifshitz transition at finite temperatures. The origin of the divergence is ascribed to the singular momentum dependence of the quasiparticle dispersion.View full abstractDownload PDF (372K) -
S. Yuan, H. De Raedt, S. Miyashita2006 Volume 75 Issue 8 Pages 084703
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThrough numerical solution of the time-dependent Schrödinger equation, we demonstrate that magnetic chains with uniaxial anisotropy support stable structures, separating ferromagnetic domains of opposite magnetization. These structures, domain walls in a quantum system, are shown to remain stable if they interact with a spin wave. We find that a domain wall transmits the longitudinal component of the spin excitations only. Our results suggests that continuous, classical spin models described by LLG equation cannot be used to describe spin wave-domain wall interaction in microscopic magnetic systems.View full abstractDownload PDF (512K) -
Kunie Ishioka, Masahiro Kitajima, Kiminori Ushida2006 Volume 75 Issue 8 Pages 084704
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSGeneration of coherent optical phonons in GaAs and Ge are systematically investigated by pump-probe reflectivity measureents. While the amplitude of the coherent optical phonon of Ge increases linearly with increasing optical excitation density, that of the coherent LO phonon of GaAs shows a saturation above a certain optical density. The coherent optical phonon of Ge follows the Raman selection rule, while that of GaAs is generated isotropically regardless of pump polarization. These differences are explained by different generation mechanisms of coherent phonons; impulsive stimulated Raman scattering and transient depletion field screening.View full abstractDownload PDF (187K) -
Minoru Itoh, Naoyuki Fujita, Yoshiyuki Inabe2006 Volume 75 Issue 8 Pages 084705
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSX-ray photoelectron spectroscopy (XPS) of metal tungstates, MWO4, has been carried out to investigate the electronic structures of scheelites (M=Pb, Ca, and Ba) and wolframites (M=Cd and Zn). Relativistic molecular orbital calculations of these tungstates have also been performed. The theoretical results are discussed in comparison with the previous band calculations, and are shown to be in satisfactory agreement with the XPS spectra. The valence and conduction bands are mainly composed of the O 2p and W 5d states, respectively, in all cases. It is stressed that the metal states contribute, to some extent, to the top of the valence band and/or the bottom of the conduction band in PbWO4, CdWO4, and ZnWO4, but such contributions are negligible in CaWO4 and BaWO4. The similarity and difference of the fundamental optical spectra among the tungstates are explained on the basis of the present results.View full abstractDownload PDF (346K) -
Hiroshi N. Kono, Yoshio Kuramoto2006 Volume 75 Issue 8 Pages 084706
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSA new mechanism for ferromagnetism in CeRh3B2 is proposed on the basis of variational Monte Carlo results. In a one-dimensional Anderson lattice where each 4f electron hybridizes with a ligand orbital between neighboring Ce sites, ferromagnetism is stabilized due to a nearly flat band which is a mixture of conduction and 4f electron states. Because of the strong spin–orbit interaction in 4f electron states, and of considerable amount of hybridization in the nearly flat band, the magnetic moments from 4f and conduction electrons tend to cancel each other. The resultant ferromagnetic moment becomes smaller as compared with the local 4f moment, and the Fermi surface in the ferromagnetic ground state is hardly affected by the presence of 4f electrons. These theoretical results are consistent with experimental observations in CeRh3B2 by neutron scattering and dHvA effects.View full abstractDownload PDF (690K) -
Yoko Miura, Riu Hirai, Yoshiaki Kobayashi, Masatoshi Sato2006 Volume 75 Issue 8 Pages 084707
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe spin-gap behavior observed in the temperature dependences of the magnetic susceptibility χ and the specific heat C of Na3Cu2SbO6 with a (distorted) honeycomb structure is analyzed in detail. The behavior is commonly observed in similar systems A3Cu2SbO6 and Na2Cu2TeO6 (A=Na, Li), and can be understood by considering both the significant Jahn–Teller distortion in the compounds and the characteristics of the shape of the electron orbits, in which spins exist. The behavior is contrasted with the antiferromagnetic transition in systems of Na3T2SbO6 and Na2T2TeO6 (T=Co, Ni). We point out that the antiferromagnetic–ferromagnetic alternating chain model successfully describes the observed magnetic behavior of Na3Cu2SbO6.View full abstractDownload PDF (461K) -
Keisuke Tomiyasu, Shinichi Itoh2006 Volume 75 Issue 8 Pages 084708
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSMagnetic excitations in CoO below TN=289 K were investigated on single crystals and a powder specimen by using inelastic neutron-scattering spectrometers installed at a steady state neutron-source and a pulsed neutron source. In single-crystal data, dispersion relations of the two magnetic excitation modes below 70 meV were determined along the symmetric directions. The magnetic excitations around 120 meV were also observed. Energy spectra on a powder specimen suggest the existence of higher order magnetic excitations spreading up to around 200 meV. The magnetic modes were analyzed in connection with the freedom of an unquenched orbital angular-momentum L of a Co2+ ion. The magnitude of the spin–orbit interaction and that of the exchange interaction obtained from the analyses are comparable, indicating that those interactions must be simultaneously considered without an approximation of the total-angular-momentum. The lowest two dispersion curves are interpreted as mixing and splitting between a dispersive excitation of Sz (S-mode) and an individual excitation of Lz (L-mode). The present experiments are the first observation of such hybridization of the S-mode and the L-mode.View full abstractDownload PDF (444K) -
Shugo Suzuki, Jin Hirosawa, Kenji Nakao2006 Volume 75 Issue 8 Pages 084709
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe study low-energy excitations in the Mott–Jahn–Teller insulator A4C60 theoretically, where A is alkali metal. A model which takes account of both the electron–electron and electron–phonon interactions is employed and the low-energy excitations are calculated by using the Tamm–Dancoff approximation. It is found that the lowest excitation corresponds to the creation of the spin-singlet Frenkel excitons at about 0.3 eV and the next lowest excitation corresponds to the creation of the spin-triplet Frenkel excitons at about 0.6 eV. It is also found that the excitations of a pair of a free electron and a free hole lie over 0.8 eV. A remarkable point is that the spin-singlet Frenkel excitons are lower in energy than the spin-triplet Frenkel excitons in A4C60 in contrast to usual insulators.View full abstractDownload PDF (115K) -
Dai Aoki, Yoshiya Homma, Hironori Sakai, Shugo Ikeda, Yoshinobu Shioka ...2006 Volume 75 Issue 8 Pages 084710
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe succeeded in growing a high-quality single crystal of NpIn3 by the In-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen (dHvA) effect. Ferromagnetic and antiferromagnetic orderings occur at TC=14 K and TN=10 K, respectively, together with another transition at T*=8 K. When the magnetic field is applied to the sample, the antiferromagnetic state is finally changed into a ferromagnetic state with two metamagnetic transitions. The antiferromagnetic ordering and two metamagnetic transitions are found to be of the first-order phase transition. In the dHvA experiments, we observed three dHvA branches with the cyclotron mass ranging from 3.4 to 14m0. These dHvA branches are discussed from a viewpoint of the 5f-localized model based on the Fermi surface of LaIn3.View full abstractDownload PDF (1190K) -
Yukio Yasui, Taketomo Kageyama, Taketo Moyoshi, Minoru Soda, Masatoshi ...2006 Volume 75 Issue 8 Pages 084711
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe unusual behavior of the anomalous Hall resistivity ρH found in the pyrochlore oxide Nd2Mo2O7 is re-analyzed. There are mainly two kinds of qualitatively interpretation of the observed behavior, one based on an idea that the ρH of this system is induced by the chirality ordering of the Mo spins and the other based on a phenomenological expression found by the present authors’ group that the ρH of the system is described as the summation of the contributions from the Mo and Nd moments. Because even after the publication of our results based on the magnetic structure analyses under the external magnetic field H, that the chirality mechanism cannot be considered to be the primary origin of the unusual behavior, the non-applicability of the mechanism still seems not to be completely fixed, we have taken further data of neutron scattering and used them, in the present analyses, together with published specific heat data and various other ones, which were also used in the previous analyses. Introducing newly the Nd–Nd exchange interaction and using clusters of 16 Nd- and 16 Mo-spins with the periodic boundary condition, we have succeeded in choosing the proper parameters to simultaneously reproduce almost all accumulated experimental data. It enables us to calculate the local Mo-spin chirality or the fictitious magnetic flux, the statistically averaged value of which should be proportional to the anomalous Hall resistivity ρH in the chirality ordering mechanism. Comparing the results of the calculation with the observed ρH, we can immediately find that the mechanism does not have the primary relevance to the Hall effect. Now, there remains a problem what the origin of the unusual behavior of the ρH is in Nd2Mo2O7.View full abstractDownload PDF (370K) -
Takashi Kuroda, Satoru Seto, Fujio Minami, Giyuu Kido2006 Volume 75 Issue 8 Pages 084712
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSThe process of energy exchange from photoinjected carriers to magnetic ions is studied by means of polarization-dependent magnetophotoluminescence in Cd1−xMnxTe (xMn=0.1). It is observed for the first time that the photothermalization of magnetic ions depends on the initial spin state of carriers, prepared by circularly polarized excitation, revealing the contribution of the spin flip-flop process to the energy transfer. Suppression of heat accumulation, exploiting low-repetition pulsed excitation, enables us to temporally resolve the spin exchange process associated with a single scattering event. Our results suggest the presence of spatial distribution in magnetization as a result of rapid carrier localization.View full abstractDownload PDF (243K) -
Kohta Ishikawa, Tsuneya Ando2006 Volume 75 Issue 8 Pages 084713
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSEffects of interactions with electrons on optical phonons are studied in an effective-mass approximation. The longitudinal mode with displacement in the axis direction is lowered in its frequency, while the transverse mode with displacement in the circumference direction is raised, in metallic nanotubes. The shifts are opposite but their absolute values are smaller in semiconducting nanotubes. Only the longitudinal mode has a considerable broadening in metallic nanotubes. In the presence of an Aharonov–Bohm magnetic flux, the broadening appears for the transverse mode and diverges when the induced gap becomes the same as the frequency of the optical phonon.View full abstractDownload PDF (194K) -
Kenjiro Hashi, Tadashi Shimizu, Atsushi Goto, Takahiro Iijima, Shinobu ...2006 Volume 75 Issue 8 Pages 084714
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSNMR measurements of 115In in Yb0.9Y0.1InCu4 were performed at 4.2 K up to 30 T with a hybrid magnet installed in National Institute for Materials Science (NIMS). Fourier-transformed (FT) spectrum at a constant magnetic field was obtained by summing a set of FT spectra with shifting the transient frequency. A first-order valence transition was observed at 22 T. Coexistence of the valence-fluctuating phase and the field-induced phase was confirmed. It was found that the proportion of the field-induced phase continues to increase even at 30 T. The effect of 4f-electron spin correlations in the field-induced phase on the spin–spin relaxation time T2 was discussed.View full abstractDownload PDF (229K) -
Jiro Kitagawa, Masahiro Ishizaka, Yutaka Kadoya, Satoshi Matsuishi, Hi ...2006 Volume 75 Issue 8 Pages 084715
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe have measured the temperature dependence of the complex THz conductivity \\ ildeσ(ω) of electron-doped 12CaO·7Al2O3 (C12A7) (carrier concentration, 5×1018 cm−3) showing the DC conductivity of Mott variable-range hopping. The complex dielectric constant of electron-doped C12A7 gradually decreases to that of undoped C12A7 with decreasing temperature, which is caused by the freeze-out of hopping carriers. The extracted \\ ildeσ(ω) stemming from the electrons was found to obey the Jonscher law between 0.3 and 1.2 THz in the measured temperature range, 50–300 K. Detailed discussions are presented by employing several pair-approximation models generally describing the frequency and temperature dependences of the power s in the Jonscher law up to GHz range, from which it has been revealed that the most plausible model is one taking into account a polaron effect. A distribution of relaxation time conjectured from the model is presented. Our results significantly suggest the extension of the use of the Jonscher law and the pair-approximation model beyond the GHz range, although some modifications may be needed for the latter.View full abstractDownload PDF (250K) -
Hiroto Adachi, Predrag Miranovic, Masanori Ichioka, Kazushige Machida2006 Volume 75 Issue 8 Pages 084716
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe study the basal-plane anisotropies of reversible magnetization and torque in a mixed state of layered d-wave superconductors based on the quasiclassical version of the BCS–Gor’kov theory. Both the longitudinal magnetization (ML) and torque (τ) show fourfold oscillations as a function of the field angle χ. The relationship between the node position and the oscillatory patterns shown by ML and τ is clarified. It is also shown that the sign of the τ(χ)-oscillation does not change between Hc1 and Hc2, while the sign of the ML(χ)-oscillation changes. The newly obtained result for τ indicates that the torque experiment can allow us to detect the in-plane anisotropies of Hc2 even in a material with strong fluctuations such as cuprate or organic superconductors, where the Hc2 itself cannot be determined experimentally.View full abstractDownload PDF (228K) -
Keisuke Nakatsuji, Akihiko Sumiyama, Yasukage Oda, Takashi Yasuda, Rik ...2006 Volume 75 Issue 8 Pages 084717
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe have investigated ac and dc magnetic susceptibilities (χac and χdc) of the heavy-fermion superconductor CePt3Si (Tc+∼0.75 K) for two single crystals that show a specific heat anomaly at Tc−∼0.4 K. One crystal shows a double transition at Tc+ and Tc− in the form of structures in the out-of-phase component of χac and in χdc measured in the cooling process. The magnetic field dependence of χac suggests that the lower transition also originates in superconductivity. In contrast, only the higher transition has been detected in susceptibility measurements of the other crystal whose specific heat has a less dominant peak near Tc− and a broad peak at Tc+. These results suggest that CePt3Si consists of two superconducting phases with different Tc’s, whose volume fraction varies from sample to sample.View full abstractDownload PDF (226K) -
R. Przenioslo, M. Regulski, I. Sosnowska2006 Volume 75 Issue 8 Pages 084718
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSWe present several modulated magnetic ordering models which all describe the high resolution neutron powder diffraction patterns of BiFeO3 with the same accuracy as the circular cycloid one proposed in [J. Phys. C 15 (1982) 4835]. These orderings are: the elliptical cycloid and the spin density wave (SDW). The ambiguity of the magnetic ordering in BiFeO3 is important in the context of recent models of the magnetoelectric coupling in perovskites [Phys. Rev. Lett. 95 (2005) 057205 and 96 (2006) 067601].View full abstractDownload PDF (75K) -
Tsuyoshi Hondou, Takenori Ueda, Yasuhiro Sakata, Nobuto Tanigawa, Tets ...2006 Volume 75 Issue 8 Pages 084801
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSIn a recent Letter [J. Phys. Soc. Jpn. 71 (2002) 432], we reported a preliminary calculation and concluded that public exposure to mobile phones can be enhanced by microwave reflection in public spaces. In this paper, we confirm the significance of microwave reflection reported in our previous Letter by experimental and numerical studies. Furthermore, we show that “hot spots” often emerge in reflective areas, where the local exposure level is much higher than average. Such places include elevators, and we discuss other possible environments including trains, buses, cars, and airplanes. Our results indicate the risk of “passive exposure” to microwaves.View full abstractDownload PDF (454K) -
Hisao Kobayashi, Xiao-Wei Zhang2006 Volume 75 Issue 8 Pages 085001
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSDownload PDF (184K) -
Shuji Ebisu, Masanori Narumi, Shoichi Nagata2006 Volume 75 Issue 8 Pages 085002
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSDownload PDF (154K) -
Masahumi Kohgi, Keitaro Kuwahara, Norio Ogita, Masayuki Udagawa, Fumit ...2006 Volume 75 Issue 8 Pages 085003
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSDownload PDF (93K) -
Hiroko Tokoro, Tomoyuki Matsuda, Seiji Miyashita, Kazuhito Hashimoto, ...2006 Volume 75 Issue 8 Pages 085004
Published: August 15, 2006
Released on J-STAGE: August 27, 2009
JOURNAL RESTRICTED ACCESSDownload PDF (159K)
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