Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 74, Issue 1
Displaying 1-50 of 71 articles from this issue
  • Jun Kondo
    2005 Volume 74 Issue 1 Pages 1-3
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Forty years ago I was trying to solve the problem of the resistance minimum in dilute magnetic alloys. In this note I shall describe experimental facts that played an essential role in solving the problem and difficulties involved in the problem that embarrassed theoretical people at that time. I shall then mention how the difficulties were overcome.
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  • Ph. Nozières
    2005 Volume 74 Issue 1 Pages 4-7
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In Kondo lattices with one magnetic impurity at every lattice site, few electrons must quench many spins. This old “exhaustion” issue has been pending for years: it now appears it does not arise: the coherence temperature at which a singlet ground state emerges is the Kondo temperature itself. We survey the evolution of that problem. We then argue that such a lattice Kondo effect governs the Mott transition from a paramagnetic metal to an incoherent spin disordered insulator. It explains the appearance of a narrow resonance in the middle of a large preformed gap. Our naive arguments can be extended to an orbitally degenerate situation: they provide a qualitative understanding of the effect discovered numerically by Capone et al. [Science 296 (2002) 2364], namely the appearance of s-wave superconductivity near the Mott transition when the atomic ground state is a singlet with no residual degeneracy.
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  • A. C. Hewson
    2005 Volume 74 Issue 1 Pages 8-15
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In recent work, we have shown that the Fermi liquid aspects of the strong coupling fixed point of the s–d and Anderson models can brought out more clearly by interpreting the fixed point as a renormalized Anderson model, characterized by a renormalized level \\ ildeεd, resonance width, \\ ildeΔ, and interaction \\ ildeU, and a simple prescription for their calculation was given using the numerical renormalization group (NRG). These three parameters completely specify a renormalized perturbation theory (RPT) which leads to exact expressions for the low temperature behaviour. Using a combination of the two techniques, NRG to determine \\ ildeεd, \\ ildeΔ, and \\ ildeU, and then substituting these in the RPT expressions gives a very efficient and accurate way of calculating the low temperature behaviour of the impurity as it avoids the necessity of subtracting out the conduction electron component. Here we extend this approach to an Anderson model in a magnetic field, so that \\ ildeεd, \\ ildeΔ, and \\ ildeU become dependent on the magnetic field. The de-renormalization of the renormalized quasiparticles can then be followed as the magnetic field strength is increased. Using these running coupling constants in a RPT calculation we derive an expression for the low temperature conductivity for arbitrary magnetic field strength.
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  • J. Kroha, P. Wölfle
    2005 Volume 74 Issue 1 Pages 16-26
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Self-consistent diagrammatic approximations to the Anderson or Kondo impurity model, using an exact pseudoparticle representation of the impurity states, are reviewed. We first discuss the infrared exponents of the pseudoparticle propagators as indicators of Fermi liquid behavior through their dependence on the impurity occupation and on magnetic field. Then we discuss the Non-Crossing Approximation (NCA), identifying its strengths, but also its fundamental shortcomings. Physical arguments as well as a perturbative renormalization group analysis suggest that an infinite parquet-type resummation of two-particle vertex diagrams, the Conserving T-Matrix Approximation (CTMA) will cure the deficiencies of NCA. We review results on the pseudoparticle spectral functions, the spin susceptibility and the impurity electron spectral function, supporting that the CTMA provides qualitatively correct results, both in the high-temperature regime and in the strong coupling Fermi liquid regime at low temperatures.
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  • Yukihiro Shimizu, Osamu Sakai
    2005 Volume 74 Issue 1 Pages 27-33
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The Kondo problem of systems with two-electron occupancy in a realistic crystalline electric field (CEF) is investigated using the numerical renormalization group method. We examine the ground state of an impurity Anderson model, which has a singlet as the lowest state and multiplets as excited states of an f2 configuration subject to a cubic CEF. When the hybridization between the f electrons and the conduction electrons is small, the ground state is a CEF-like singlet state. For a large hybridization, on the other hand, the ground state becomes a Kondo-like singlet state. The hybridization with Γ8 symmetry plays an important role in the Kondo effect in this model. The transition between the two types of singlet states is accompanied by a lowering of the energy scale when the Γ8 type hybridization is relatively large. The non-Fermi liquid behavior of a model, which has a non-Kramers lowest state of an f2 configuration subject to the tetragonal CEF, is also investigated.
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  • J. W. Allen
    2005 Volume 74 Issue 1 Pages 34-48
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The Kondo resonance is the spectral manifestation of the Kondo properties of the impurity Anderson model, and also plays a central role in the dynamical mean-field theory (DMFT) for correlated electron lattice systems. This article presents an overview of electron spectroscopy studies of the resonance for the 4f electrons of cerium compounds, and for the 3d electrons of V2O3, including beginning efforts at using angle resolved photoemission to determine the k-dependence of the resonance. The overview includes the comparison and analysis of spectroscopy data with theoretical spectra as calculated for the impurity model and as obtained by DMFT, and the Kondo volume collapse calculation of the cerium α–γ phase transition boundary, with its spectroscopic underpinnings.
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  • Satoshi Yotsuhashi, Masatsugu Kojima, Hiroaki Kusunose, Kazumasa Miyak ...
    2005 Volume 74 Issue 1 Pages 49-58
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    New aspects of the two-level Kondo (TLK) effect and the strongly coupled local electron–phonon (LEP) system are studied by the Wilson numerical renormalization group method. It turns out that there exist strong-coupling fixed points for both systems which can be mapped on the antiferromagnetic pseudo-spin sd-model, if the bare coupling is chosen moderately strong. In the case of TLK model, it is found that there exsist two different strong-coupling regions one of which is found for the first time, and that there exists a zero-coupling region as well. In the case of LEP system, in which three low-lying phonon levels are taken into account, it is found that there exist a strong-coupling fixed point which corresponds to the effective potential of ionic motion with double-well character. An analysis of LEP system based on the poorman’s scaling with Lee algebra of SU(3) is also discussed.
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  • Ian Affleck
    2005 Volume 74 Issue 1 Pages 59-66
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Despite the fact that the low energy behavior of the basic Kondo model cannot be studied perturbatively it was eventually shown by Wilson, Anderson, Nozières and others to have a simple “local Fermi liquid theory” description. That is electronic degrees of freedom become effectively non-interacting in the zero energy limit. However, generalized versions of the Kondo model involving more than one channel or impurity may exhibit low energy behavior of a less trivial sort which can, nonetheless, be solved exactly using either Bethe ansatz or conformal field theory and bosonization techniques. Now the low energy limit exhibits interacting many body behavior. For example, processes in which a single electron scatters off the impurity into a multi electron–hole state have a non-vanishing (and sometimes large) amplitude at zero energy. This corresponds to a rare solveable example of non-Fermi liquid behavior. Essential features of these phenomena are reviewed here.
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  • Satoshi Fujimoto, Norio Kawakami
    2005 Volume 74 Issue 1 Pages 67-72
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We review some exact results on Kondo impurity systems derived from Bethe-ansatz solutions and boundary conformal field theory with particular emphasis on universal aspects of the phenomenon. The finite-size spectra characterizing the low-energy fixed point are computed from the Bethe-ansatz solutions of various models related to the Kondo problem. Using the finite-size scaling argument, we investigate their exact critical properties. We also discuss that a universal relation between the Kondo effect and the impurity effect in one-dimensional quantum systems usefully expedites our understanding of these different phenomena.
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  • Akira Furusaki
    2005 Volume 74 Issue 1 Pages 73-79
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Quantum impurity problems in Tomonaga–Luttinger liquids (TLLs) are reviewed with emphasis on their analogy to the Kondo problem in Fermi liquids. First, the problem of a static impurity in a spinless TLL is considered, which is related to the model studied in the context of the macroscopic quantum coherence. In the low-energy limit the TLL is essentially cut into two pieces when interaction is repulsive. The orthogonality catastrophe in a TLL is then discussed. Finally, the Kondo effect of a spin-1⁄2 impurity in a one-dimensional repulsively interacting electron liquids (a spinful TLL) is reviewed. Regardless of the sign of the exchange coupling, the impury spin is completely screened in the ground state. The leading low-temperature contributions to thermodynamic quantities come from boundary contributions of a bulk leading irrelevant operator.
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  • O. Újsághy, A. Zawadowski
    2005 Volume 74 Issue 1 Pages 80-87
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Following the discovery of the Kondo effect the bulk transport and magnetic behavior of the dilute magnetic alloys have been successfully described. In the last fifteen years new directions have been developed as the study of the systems of reduced dimensions and the artificial atoms so called quantum dots. In this review the first subject is reviewed starting with the scanning tunneling microscope (STM) study of a single magnetic impurity. The next subject is the reduction of the amplitude of the Kondo effect in samples of reduced dimension which was explained by the surface magnetic anisotropy which blocks the motion of the integer spin nearby the surface. The electron dephasing and energy relaxation experiments are discussed with the possible explanation including the surface anisotropy, where the situation in cases of integer and half-integer spins is very different. Finally, the present situation of the theory of dynamical structural defects is briefly presented which may lead to two-channel Kondo behavior.
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  • Satoshi Sasaki, Seigo Tarucha
    2005 Volume 74 Issue 1 Pages 88-94
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The Kondo effect associated with state degeneracy is studied for a two-dimensional harmonic quantum dot. State degeneracies between a spin singlet and triplet states, between two spin doublet states, and between a spin doublet and quadruplet states are induced by magnetic field. For the first two degenracies, strong enhancement of the Kondo effect is observed. The estimated Kondo temperature for the “doublet–doublet” degeneracy with an odd electron number is similar to that for the “singlet–triplet” degeneracy with an even electron number, indicating that a total of four-fold spin and orbital degeneracy for both cases accounts for the similar enhancement of the Kondo temperature. The Kondo effect generally gives rise to enhanced conductnace and a zero-bias peak of differential conductance in the Coulomb valley. In contrast, enhacned conductance but a zero-bias dip is observed for the third “doublet–quadruplet” degeneracy. This can be due to Zeeman splitting but no clear interpretation is reached yet.
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  • Mikio Eto
    2005 Volume 74 Issue 1 Pages 95-102
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We theoretically study enhancement mechanisms of the Kondo effect in multilevel quantum dots. In quantum dots fabricated on semiconductors, the energy difference between discrete levels Δ is tunable by applying a magnetic field. With two orbitals and spin 1⁄2 in the quantum dots, we evaluate the Kondo temperature TK as a function of Δ, using the scaling method. TK is maximal around Δ=0 and decreases with increasing |Δ|, following a power law, TK(Δ)=TK(0)·(TK(0)⁄|Δ|)γ, which is understood as a crossover from SU(4) to SU(2) Kondo effect. The exponents on both sides of a level crossing, γL and γR, satisfy a relation of γL·γR=1. We compare this enhanced Kondo effect with that by spin-singlet–triplet degeneracy for an even number of electrons, to explain recent experimental results using vertical quantum dots.
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  • Wataru Izumida, Osamu Sakai
    2005 Volume 74 Issue 1 Pages 103-109
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We review recent theoretical studies on the Kondo effect in tunneling through quantum dots. The calculation is carried out using the numerical renormalization group method. It is shown that two Coulomb peaks merge into a plateau for the case of an odd number of electrons in the dot. The anomaly of tunneling conductance in an even number of electrons with local spin singlet–triplet degeneracy is studied. The two-impurity Kondo effect, in which a competition between the Kondo coupling and two localized spins coupling occurs, causes a conductance peak in the double quantum dot. The Aharonov–Bohm (AB) oscillation in the conductance of a quantum dot embedded in an AB circuit is also studied.
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  • Akira Oguri
    2005 Volume 74 Issue 1 Pages 110-117
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In this paper, we describe a recent development in a Fermi liquid theory for the Kondo effect in quantum dots under a finite bias voltage V. Applying the microscopic theory of Yamada and Yosida to a nonequilibrium steady state, we derive the Ward identities for the Keldysh Green’s function, and determine the low-energy behavior of the differential conductance dIdV exactly up to terms of order (eV)2 for the symmetric Anderson model. These results are deduced from the fact that the Green’s function at the impurity site is a functional of a nonequilibrium distribution feff(ω), which at eV=0 coincides with the Fermi function. Furthermore, we provide an alternative description of the low-energy properties using a renormalized perturbation theory (RPT). In the nonequilibrium state the unperturbed part of the RPT is determined by the renormalized free quasiparticles, the distribution function of which is given by feff(ω). The residual interaction between the quasiparticles \\widetildeU, which is defined by the full vertex part at zero frequencies, is taken into account by an expansion in the power series of \\widetildeU. We also discuss the application of the RPT to a high-bias region beyond the Fermi-liquid regime.
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  • A. Rosch, J. Paaske, J. Kroha, P. Wölfle
    2005 Volume 74 Issue 1 Pages 118-126
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    While the properties of the Kondo model in equilibrium are very well understood, much less is known for Kondo systems out of equilibrium. We study the properties of a quantum dot in the Kondo regime, when a large bias voltage V and/or a large magnetic field B is applied. Using the perturbative renormalization group generalized to stationary nonequilibrium situations, we calculate renormalized couplings, keeping their important energy dependence. We show that in a magnetic field the spin occupation of the quantum dot is non-thermal, being controlled by V and B in a complex way to be calculated by solving a quantum Boltzmann equation. We find that the well-known suppression of the Kondo effect at finite V>>TK (Kondo temperature) is caused by inelastic dephasing processes induced by the current through the dot. We calculate the corresponding decoherence rate, which serves to cut off the RG flow usually well inside the perturbative regime (with possible exceptions). As a consequence, the differential conductance, the local magnetization, the spin relaxation rates and the local spectral function may be calculated for large V,B>>TK in a controlled way.
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  • Tatsuya Fujii, Kazuo Ueda
    2005 Volume 74 Issue 1 Pages 127-135
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We investigate nonequilibrium transport through a dot in a finite magnetic field in a weak correlation regime by using the self-consistent perturbation theory in the Keldysh formalism. Separation of the density of states between the up and down spins becomes smaller gradually and ends up with the Zeeman energy as increasing the bias voltage. Concerning the differential conductance the zero-bias peak splits into two peaks when magnetic field is increased. The critical field for the splitting decreases as the Coulomb interaction is increased.
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  • D. Vollhardt, K. Held, G. Keller, R. Bulla, Th. Pruschke, I. A. Nekras ...
    2005 Volume 74 Issue 1 Pages 136-146
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Dynamical mean-field theory (DMFT) is a non-perturbative technique for the investigation of correlated electron systems. Its combination with the local density approximation (LDA) has recently led to a material-specific computational scheme for the ab initio investigation of correlated electron materials. The set-up of this approach and its application to materials such as (Sr,Ca)VO3, V2O3, and Cerium is discussed. The calculated spectra are compared with the spectroscopically measured electronic excitation spectra. The surprising similarity between the spectra of the single-impurity Anderson model and of correlated bulk materials is also addressed.
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  • Gabriel Kotliar
    2005 Volume 74 Issue 1 Pages 147-154
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Dynamical mean field theory (DMFT) relates extended systems (bulk solids, surfaces and interfaces) to quantum impurity models (QIM) satisfying a self-consistency condition. This mapping provides an economic description of correlated electron materials. It is currently used in practical computations of physical properties of real materials. It has also great conceptual value, providing a simple picture of correlated electron phenomena on the lattice, using concepts derived from quantum impurity models such as the Kondo effect. DMFT can also be formulated as a first principles electronic structure method and is applicable to correlated materials.
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  • Hiroshi Kontani, Kosaku Yamada
    2005 Volume 74 Issue 1 Pages 155-166
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The Kondo effect has been playing an important role in strongly correlated electon systems. The important point is that the magnetic impurity in metals is a typical example of the Fermi liquid. In the system the local spin is conserved in the ground state and continuity with respect to Coulomb repulsion U is satisfied. This nature is satisfied also in the periodic systems as far as the systems remain as the Fermi liquid. This property of the Fermi liquid is essential to understand the cuprate high-Tc superconductors (HTSC). On the basis of the Fermi liquid theory we develop the transport theory such as the resistivity and the Hall coefficient in strongly correlated electron systems, such as HTSC, organic metals and heavy Fermion systems. The significant role of the vertex corrections for total charge- and heat-currents on the transport phenomena is explained. By taking the effect of the current vertex corrections into account, various typical non-Fermi-liquid-like transport phenomena in systems with strong magnetic and/or superconducting flucutations are explained within the Fermi liquid theory.
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  • Frank Steglich
    2005 Volume 74 Issue 1 Pages 167-177
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In this contribution we recall some of the early work devoted to Ce-based Kondo alloys which subsequently lead to thorough investigations on so-called “Kondo-lattice” systems like CeAl2, CeAl3 and CeCu2Si2, subsequently referred to as heavy-fermion metals. We then address the physical properties of the first heavy-fermion superconductor CeCu2Si2 and discuss the relationship of its superconductivity with both a spin-density-wave-type quantum critical point and a weak valence transition of Ce that occurs at high pressure. Finally, we introduce the isostructural Kondo-lattice system YbRh2Si2, displaying a novel type of quantum critical behavior which appears to be detrimental to superconductivity.
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  • J. Flouquet, A. Barla, R. Boursier, J. Derr, G. Knebel
    2005 Volume 74 Issue 1 Pages 178-185
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In the first step, experiments on a single cerium or ytterbium Kondo impurity reveal the importance of the Kondo temperature by comparison to other type of couplings like the hyperfine interaction, the crystal field and the intersite coupling. The extension to a lattice is discussed. Emphasis is given on the fact that the occupation number nf of the trivalent configuration may be the implicit key variable even for the Kondo lattice. Three (P,H,T) phase diagrams are discussed: CeRu2Si2, CeRhIn5 and SmS.
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  • Y. Kitaoka, S. Kawasaki, T. Mito, Y. Kawasaki
    2005 Volume 74 Issue 1 Pages 186-199
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We review the studies on the emergent phases of superconductvity and magnetism in the f-electron derived heavy-fermion (HF) systems by means of the nuclear-quadrupole-resonance (NQR) under pressure. These studies have unraveled a rich variety of the phenomena in the ground state of HF systems. In this article, we highlight the novel phase diagrams of magnetism and unconventional superconductivity (SC) in CeCu2Si2, HF antiferromagnets CeRhIn5, and CeIn3. A new light is shed on the difference and common features on the interplay between magnetism and SC on the magnetic criticality.
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  • Junya Otsuki, Hiroaki Kusunose, Yoshio Kuramoto
    2005 Volume 74 Issue 1 Pages 200-208
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Possible Kondo effect in Pr skutterudite is studied with attention to characteristic features of low-lying crystalline electric field (CEF) levels and the conduction band. A mechanism for the small CEF splitting between a singlet and a triplet is proposed as combination of the point-charge interaction and hybridization of 4f with ligand p states. Provided 4f3 configurations dominate over 4f1 as intermediate states, pf hybridization favors the triplet, while point-charge interaction favors the singlet. For realistic parameters for hybridization as well as 4f1 and 4f3 levels, these singlet and triplet can form a nearly degenerate pseudo-quartet. It is found that one of two spin 1⁄2 objects composing the pseudo-quartet has a ferromagnetic exchange, while the other has an antiferromagnetic exchange with conduction electrons. The magnitude of each effective exchange depends strongly on a parameter characterizing the triplet wave function under the Th symmetry. It is argued that differences of this parameter among Pr skutterdudites are responsible for the apparent diversity of their physical properties. Numerical renormalization group is used to derive the renormalization flows going toward singlet, doublet, triplet or quaret according to the CEF splitting and exchange interactions.
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  • Yuji Aoki, Hitoshi Sugawara, Harima Hisatomo, Hideyuki Sato
    2005 Volume 74 Issue 1 Pages 209-221
    Published: January 15, 2005
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    Novel Kondo-like behaviors realized in the Pr-based filled skutterudites are reviewed based on the electronic transport properties, specific heat and de Haas–van Alphen (dHvA) experiments, along with the band structure calculations. As references, the experiments on the related La- and Ce-filled skutterudites are also studied and discussed. PrRu4Sb12 is an ordinary BCS superconductor without f-electron-derived mass enhancement. PrRu4P12 exhibits a metal–semiconductor transition at 62 K and an anomaly with a small characteristic energy at low temperatures. The Fermi surface (FS) topology is very similar between the first known heavy fermion superconductor PrOs4Sb12 and the reference compound LaOs4Sb12, suggesting the well-localized character of 4f-electrons in PrOs4Sb12. In contrast, the topology of the FS of PrFe4P12, which exhibits apparent Kondo behaviors at high temperatures and the field-induced heavy fermion state at low temperatures, is as a whole different from that of LaFe4P12, although partial similarity is visible between the two. For both PrFe4P12 and PrOs4Sb12, de Haas–van Alphen experiments revealed strongly enhanced cyclotron effective masses, in reasonable agreement with the large specific heat coefficients. The ground state is settled to be non-magnetic, and anomalous antiferro-electronic-quadrupole (orbital) ordering of Pr-ions are realized in zero field for PrFe4P12 and under magnetic fields for PrOs4Sb12, suggesting that the quadrupole degrees of freedom play key roles in the heavy-fermion and the exotic superconducting behaviors. The novel features realized in the Pr-filled skutterudites are discussed in relation with the unique crystal structures.
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  • M. Brian Maple
    2005 Volume 74 Issue 1 Pages 222-238
    Published: January 15, 2005
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    A series of experiments on strongly correlated electron phenomena in f-electron materials, performed during the past three and one half decades, are briefly reviewed. The phenomena considered include the Kondo effect in superconductors, demagnetization of rare earth ions in metals, valence fluctuations of rare earth ions in metals, heavy fermion superconductors, and non-Fermi liquid behavior in f-electron systems. Recent experiments on heavy fermion behavior and unconventional superconductivity in the filled skutterudite compound PrOs4Sb12 are also discussed. The fundamental interactions responsible for the Kondo effect play a prominent role in the physics of strongly correlated electron phenomena in f-electron materials.
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  • Anton Sakovich, Sergei Sakovich
    2005 Volume 74 Issue 1 Pages 239-241
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We prove that the Schäfer–Wayne short pulse equation (SPE), which describes the propagation of ultrashort optical pulses in nonlinear media, is integrable. First, we discover a Lax pair of the SPE that is found to be of the Wadati–Konno–Ichikawa type. Second, we construct a chain of transformations that relates the SPE with the sine-Gordon equation.
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  • Jong-Hoon Huh, Jiang Xin, Yusril Yusuf, Shoichi Kai
    2005 Volume 74 Issue 1 Pages 242-245
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We report electromechanical effects in a swollen polydomain liquid crystalline elastomer (POLY-LCE). Owing to the director reorientation, we could directly observe its deformation in the unconstrained elastomer gel state. Using optical image analysis, the deformation amplitude, threshold voltage, and temporal characteristics of the POLY-LCE were quantitatively measured with varying voltage and temperature. From the experimental results we discuss the deformation mechanism and property of the POLY-LCE.
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  • Shotaro Sanada, Yuji Aoki, Hidekazu Aoki, Akihisa Tsuchiya, Daisuke Ki ...
    2005 Volume 74 Issue 1 Pages 246-249
    Published: January 15, 2005
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    Specific heat and transport measurements have revealed an unconventional heavy-fermion (HF) state in SmOs4Sb12 single crystals. The electronic specific-heat coefficient (γ=0.82 J/K2 mol) and the coefficient (A) of the quadratic temperature dependence of electrical resistivity are largely enhanced, although the ratio Aγ−2 is reduced from the Kadowaki–Woods ratio of HF materials. Both γ and A do not show any significant decrease in applied field in contrast with Ce-based HF compounds, suggesting an unconventional origin of the heavy quasiparticles. A weak ferromagnetic ordering sets in below ∼3 K, probably originating in the itinerant quasiparticles.
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  • Jun Ohara, Shoji Yamamoto
    2005 Volume 74 Issue 1 Pages 250-253
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The optical conductivity of photogenerated solitons in quasi-one-dimensional halogen-bridged binuclear metal (MMX) complexes is investigated with particular emphasis on a comparison between the two family compounds R4[Pt2(pop)4XnH2O (X=Cl, Br, I; R=NH4, Na, K, …; pop = diphosphonate = P2O5H22−) and Pt2(dta)4I (dta = dithioacetate = CH3CS2). Soliton-induced absorption spectra for the pop complexes should split into two bands, while those for the dta complex should consist of a single band.
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  • Kazumasa Miyake, Hiroshi Kohno
    2005 Volume 74 Issue 1 Pages 254-258
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    It is shown that the quasi-universal ratio q=limT→0eSC∼±1 of the Seebeck coefficient to the specific heat in the limit of T=0 observed in a series of strongly correlated metals can be understood on the basis of the Fermi liquid theory description. In deriving this result, it is crucial that a relevant scattering arises from impurities, but not from the mutual scattering of quasiparticles. The systematics of the sign of q is shown to reflect the sign of the logarithmic derivative of the density of states and the inverse mass tensor of the quasiparticles, explaining the systematics of experiments. In particular, the positive sign of q for Ce-based and f3-based heavy fermions, and the negative sign for Yb-based and f2-based heavy fermions, are explained. The case of non-Fermi liquid near the quantum critical point (QCP) is briefly mentioned, showing that the ratio q decreases considerably toward antiferromagnetic QCP while it remains essentially unchanged for the ferromagnetic QCP or QCP due to a local criticality.
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  • Tamaki Ise, Hiroshi Akera, Hidekatsu Suzuura
    2005 Volume 74 Issue 1 Pages 259-262
    Published: January 15, 2005
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    The spatial variations of the electron temperature in the vicinity of metallic current contacts in a quantum Hall system are calculated based on thermohydrodynamics with an energy gain. It is shown that, at large currents, hot spots with high electron temperatures appear at diagonally opposite corners of a sample. At small currents, however, the electron temperature at one of the corners is lower than the lattice temperature, while that at the other corner is higher than the lattice temperature. As a function of the chemical potential, the electron temperature at each corner shows quantum oscillations.
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  • Terutaka Goto, Yuichi Nemoto, Kei Onuki, Kazuhiro Sakai, Takashi Yamag ...
    2005 Volume 74 Issue 1 Pages 263-266
    Published: January 15, 2005
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    We have made ultrasonic measurements on a filled skutterudite PrOs4Sb12 showing a heavy fermion superconductivity at TC=1.85 K. The softening of the elastic constant with decreasing temperature has been found above TC. The (C11C12)⁄2 in applying magnetic fields along the [110] axis at 1.0 K exhibits a minimum around 8 T, which is well accounted for by the one-ion quadrupolar susceptibility reflecting the level crossing of one of an excited Γ4(2) triplet to a ground state Γ1 singlet. The softening of (C11C12)⁄2 proportional to reciprocal temperature just above TC may be dominated by the tunneling of an off-center Pr-ion in an Sb-icosahedron cage.
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  • Tomoyuki Sasaki, Tetsuya Yokoo, Susumu Katano, Jun Akimitsu
    2005 Volume 74 Issue 1 Pages 267-270
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Static and dynamical spin properties in a hole-doped one-dimensional Haldane chain system have been investigated by magnetization and neutron scattering measurements on antiferromagnetic Nd2−xCaxBaNiO5. Spin-glass-like weak ferromagnetic behavior and an incommensurate dynamical structure were observed, which are similar to those reported in the Haldane system Y2−xCaxBaNiO5. A novel excitation, moreover, has been revealed at 10 meV because of complete the shift in the Haldane gap due to three-dimensional antiferromagnetic ordering, which possibly provides a total picture of a hole-induced quantum Haldane chain.
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  • Keitaro Sakurazawa, Hiroshi Kontani, Tetsuro Saso
    2005 Volume 74 Issue 1 Pages 271-274
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We propose a mechanism for the magnetic-field-induced antiferromagnetic (AF) state in a two-dimensional Hubbard model in the vicinity of the AF quantum critical point (QCP), using the fluctuation-exchange (FLEX) approximation by taking the Zeeman energy due to the magnetic field B into account. In the vicinity of the QCP, we find that the AF correlation perpendicular to B is enhanced, whereas that parallel to B is reduced. This fact means that the finite magnetic field increases TN, with the AF order perpendicular to B. The increment of TN can be understood in terms of the reduction of both quantum and thermal fluctuations due to the magnetic field, which is caused by the self-energy effect within the FLEX approximation. The present study naturally explains the increment of TN in CeRhIn5 under the magnetic field found recently. We will also discuss a relation to some organic metals.
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  • Satoshi Iikubo, Masafumi Ito, Akito Kobayashi, Masatoshi Sato, Kazuhis ...
    2005 Volume 74 Issue 1 Pages 275-278
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The magnetic excitation spectra χ″(q,ω) of YBa2Cu3Oy and La214 systems have been studied. For a sample of the latter system, La1.88Sr0.12CuO4, χ″(q,ω) has been measured up to ∼30 meV. Existing data of these two kinds of system have been analyzed at energies up to the values far above ωr, around which χ″(q,ω) exhibits the commensurate peak. In the analyses, we have used the phenomenological expression of the generalized magnetic susceptibility χ(q,ω)=χ0(q,ω)⁄{1+J(q0(q,ω)}, where χ0(q,ω) is the susceptibility of the electrons without the exchange coupling J(q) among them. In the energy region up to ∼ωr, it has been reported by the authors’ group that the expression can explain the characteristics of the q- and ω-dependences of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here, it is also pointed out that the expression can reproduce the rotation of the four incommensurate peaks of χ″(q,ω) within the a*b* plane about (π⁄a,π⁄a) [or so-called (π,π)] point by 45°, which occurs as ω goes to the region far above ωr from an energy below ωr. This indicates that for the rotation, “stripe” correlation is not required. For La214, the observed and calculated results of χ″(q,ω) are comparatively discussed up to the ω region far above ωr. These results indicate that for YBCO, the characteristics of χ″(q,ω) can be explained qualitatively by the above expression throughout the ω region studied, while for the La214 system, effects of “stripes” on χ″(q,ω), which cannot be explained by the expression, are more significant in the low-energy region of ω (<ωr) than at high energies.
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  • Shinichi Itoh, Ryoichi Kajimoto, Mark A. Adams
    2005 Volume 74 Issue 1 Pages 279-282
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Magnetic fractons in the near-percolating three-dimensional (3D) Heisenberg antiferromagnet, RbMn0.4Mg0.6F3, were studied using inelastic neutron scattering with a high energy resolution (ΔE=17.5 μeV) and at low temperature (T=1.5 K). It was demonstrated that the fractons follow the dispersion relation of qz (q being the wave number). The observed exponent, z=2.5, was in good agreement with the fractal dimension of the 3D system (Df=2.48), as predicted by theory.
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  • Yoshitaka Maeda, Masaki Oshikawa
    2005 Volume 74 Issue 1 Pages 283-286
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    We formulate a direct and systematic perturbation theory on the shift of the main paramagnetic peak in electron spin resonance, and derive a general expression up to the second order. It is applied to the one-dimensional XXZ and transverse Ising models in the high field limit, to obtain explicit results including the polarization dependence at arbitrary temperature.
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  • Yan-ze Peng
    2005 Volume 74 Issue 1 Pages 287-291
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    A general solution involving three arbitrary functions is first obtained for the generalization of integrable (2+1)-dimensional dispersive long wave equations by means of WTC truncation method. Exact periodic wave solutions are then expressed as rational functions of the Jacobi elliptic functions. For the first time the interaction of Jacobi elliptic waves is studied and found to be nonelastic! Limit cases are studied and some interesting, new solitary structures are revealed. The interactions of between two dromions, between dromion and solitoff and between y-periodic solitons are all nonelastic, and x-periodic solitons can propagate steadily. It is shown that the Jacobi elliptic wave solutions can be viewed as the generalization of dromion, dromion-solitoff and periodic solitons.
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  • Hidetsugu Sakaguchi, Mitsuaki Tamura
    2005 Volume 74 Issue 1 Pages 292-298
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Scattering of solitons and dark solitons by potential walls is studied in the nonlinear Schrödinger equation under various conditions. We investigate the conditions under which solitons are split into two solitons at the potential wall. We find that a soliton can be trapped in an interspace between two potential walls. A dark soliton can also be scattered at the potential wall. Similarly to a bright soliton, a dark soliton can pass through more easily the potential wall, as the width of the dark soliton is larger. A dark soliton can run away spontaneously from an interspace between the two potential walls. We also study the motion of a two-dimensional soliton in a two-dimensional quintic nonlinear Schrödinger equation. We find the coherent tunneling through a potential wall, and the refraction corresponding to Newton’s refraction theory.
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  • Shuifa Shen, Yan Li, Shuanghui Shi, Jiahui Gu, Jingyi Liu
    2005 Volume 74 Issue 1 Pages 299-306
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The decay of 72Ga has been investigated by means of γ-ray spectroscopy. The 72Ga nuclei were produced through the 71Ga(n, γ)72Ga reaction. The Compton-suppressed spectrometer and High-purity Ge detectors have been used singly and in coincidence, respectively, to study γ-rays in the β decay of 72Ga to 72Ge. 93 γ-rays, among which 7 were observed for the first time, were reported. A decay scheme of 72Ga including 4 new levels is proposed which accommodates 87 of these transitions. Spins and parities for new levels are proposed from calculated logft values, modes on the observed decay, and some nuclear reaction experiment results. Combining with the high-spin states observed by the in-beam γ-ray spectroscopy of a previous decay work, the structure of the excited positive-parity yrast states of 72Ge is discussed in the framework of the projected shell model.
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  • Giovanni Fazio, Giorgio Giardina, Antonino Lamberto, Carmelo Sacc&agra ...
    2005 Volume 74 Issue 1 Pages 307-316
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The effects of entrance channel with different projectile and target nuclei combinations on the fission of the 22090Th*, 254102No* and 256104Rf* compound nuclei are investigated. The dependence of the de-excitation of the compound nucleus on the dynamics of the entrance channel is analyzed for the first time. We find that the fission branching ratio Γf⁄Γtot of the compound nucleus formed in the two different reactions with massive nuclei is different due to the dynamical effects in the entrance channel even at the same excitation energy E*. It is caused by the different partial fusion cross section σlfus(E) for those reactions. Consequently, the excitation function of evaporation residues measured in such reactions is strongly related to the effect of the entrance channel. This phenomenon is explained by the dependence of the capture and fusion cross sections on the orbital angular momentum of collision.
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  • Dae-Soung Kim, Hak-Chul Kang
    2005 Volume 74 Issue 1 Pages 317-320
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Photoelectron angular distribution asymmetry parameters β for the process leaving the ions in the B2+ np and ns (n=2 and 3) states from the ground and excited 2s2p 1,3P states of Be-like B+ ion have been calculated. The other final ionic states of B2+ are states leading to a constant β=2. A noniterative variational R-matrix approximation has been used for the present calculation of transition strengths. With almost overlapped agreement between the length and velocity gauges, autoionizing doubly excited resonance structures converging to B2+ 3s, 3p, and 3d thresholds are clearly appeared in the present β parameters.
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  • A. Igarashi, A. Ohsaki, S. Nakazaki
    2005 Volume 74 Issue 1 Pages 321-325
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    The electron-impact transitions between the n=2 fine-structure levels of hydrogenic ions are calculated by an improved close coupling scheme that accounts for the electron-exchange effect. It is found that the electron-exchange effect is relatively unimportant in the optically allowed transitions, as expected from its long-range nature, but represents a considerable contribution to the cross-sections of the optically forbidden transitions, where the contribution of low partial waves is more significant. Hence, a close coupling calculation including the exchange effect is required for low partial waves.
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  • Yuko Tohyama, Tetsuo Nagata
    2005 Volume 74 Issue 1 Pages 326-332
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    As a confirmative study on electron impact emission of the second positive band group (2PG) of N2 molecules, absolute emission cross section for the 2P(0,0) band and intensity ratios 2P(v′,v″)⁄2P(0,0) have been measured. The absolute measurement has been made directly using a standard light source. From these results, the cross sections for excitation of C3Πu (v′=0, 1) vibrational states have been determined. Emphasis was placed on measurements under single-collision condition. Experimental errors have been assessed in some detail. The absolute 2P(0,0) cross section measured has the peak value of (11.1±1.1)×10−18 cm2. This value is in good agreement with measurements reported recently by other two research groups. From the present and the two recent results, which were measured at low N2 pressure and for which estimated errors are given, a weighted averaging value is calculated to be (11.0±0.7)×10−18 cm2 as a recommended emission cross section for 2P(0,0) band.
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  • Reima Iwatsu
    2005 Volume 74 Issue 1 Pages 333-344
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Numerical study was conducted for steady swirling flows of viscous incompressible fluid confined in cylindrical containers driven by the bottom wall rotating at constant angular velocity with top free surface. The flow axisymmetry and the free-slip boundary condition is assumed at the top flat surface of the cylinder. Parametric computation was performed over a wide range of the Reynolds number Re and the radius to height aspect ratio h which covers parameter range not previously studied. Steady solutions disclosed a variety of flow patterns which include corner and surface bubbles with inner structures not noticed in the previous studies. Associated parameter regions are mapped on the parameter plane (h,Re) as a flow state diagram. It is shown that the bifurcation diagram is more complicated than previously believed. Comparison with the previous experimental and numerical studies is discussed in detail.
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  • Shinichiro Yanase, Rabindra Nath Mondal, Yoshito Kaga, Kyoji Yamamoto
    2005 Volume 74 Issue 1 Pages 345-358
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Flows through a curved rectangular duct for the aspect ratio l=2 are numerically studied by use of the spectral method with and without a temperature difference between the vertical outer and inner sidewalls. We find three branches of steady solutions for the case without the temperature difference (isothermal case). Then we investigate linear stability of the steady solutions and find that only a portion of one steady solution branch is linearly stable but other branches are unstable. We obtain five branches of steady solutions for the case with the temperature difference (non-isothermal case) for the Grashof number Gr=100. Linear stability shows that only a portion of one of them is linearly stable while other branches are unstable like the isothermal case. The change of the flow state, as the Dean number Dn is increased, obtained by time evolution calculations, is found to be similar for both the isothermal and non-isothermal cases. When there is no stable steady solution, the time evolution calculations show that typical transition occurs from a steady flow to a chaotic state through a periodic flow when Dn is increased whether the system is isothermal or non-isothermal.
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  • Takeshi Miyazaki, Hiroshi Taira, Takuya Niwa, Naoya Takahashi
    2005 Volume 74 Issue 1 Pages 359-367
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    Refinements on the quasi-geostrophic wire-vortex model are proposed. Each coherent vortex is modeled by a straight wire of finite length. The dynamics of N wire-vortices is a canonical Hamiltonian system of 2N degrees of freedom. We adapt the Gaussian integration method in the evaluation of the mutual energy integrals, instead of the moment approximation used in the previous wire model. The accuracy of integration is improved drastically, even if two wire-vortices are placed very close. The refined model can circumvent the singular behavior of a counter-rotating vortex pair, predicted by the previous wire moment model. We also introduce a realistic relation between the inclination angle and the vortex-slenderness parameter, assuming that each wire-vortex is a prolate spheroid. The latter refinement enables us to model fatter vortices more accurately.
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  • Lizhu Tong, Kenichi Nanbu
    2005 Volume 74 Issue 1 Pages 368-374
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    In materials processing plasmas, many plasma reactors have the shape of a finite cylinder. By the use of the variational method and the boundary-layer theory, here is proposed an analytical solution method of axisymmetrical Poisson equation for the electric field with thin sheaths. The method is extremely faster than the various methods based on the finite difference equation. The present method makes the numerical simulation of materials processing plasmas much more easier.
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  • H. B. Guo, B. X. Liu
    2005 Volume 74 Issue 1 Pages 375-381
    Published: January 15, 2005
    Released on J-STAGE: November 13, 2007
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    A realistic n-body potential is derived for the equilibrium immiscible Co–Ag system through fitting its cross potential to some physical properties obtained from ab initio calculations for a few possible nonequilibrium Co–Ag alloys. Based on the derived Co–Ag potential, molecular dynamics simulations reveal that a Co-/Ag-based solid solution can retain its atomic homogeneity up to a critical atomic ratio of 9/12 at.% of Ag/Co, over which the solute atoms begin to segregate and that when the solute atoms exceed 12/18 at.% of Ag/Co, the solid solution becomes unstable and transforms into an amorphous alloy featuring also an inhomogeneous atomic structure, thus predicting a glass-forming range to be within 12–82 at.% of Ag. Moreover, a formation energy diagram is constructed to compare the energetic states of the possible nonequilibrium Co–Ag alloys. For the homogeneous Co-/Ag-based solid solution, a cage-like configuration is proposed to have one solvent atom isotropically surrounded by three nearest shells of solute atoms, and interestingly, the atomic ratio of the proposed configuration is very close to the critical composition of segregation determined by simulations.
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