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Ken-ichi Maruno, G. Reinout W. Quispel
2006 Volume 75 Issue 12 Pages
123001
Published: December 15, 2006
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We find that certain higher-order mappings arise as reductions of the integrable discrete A-type KP (AKP) and B-type KP (BKP) equations. We find conservation laws for the AKP and BKP equations, then we use these conservation laws to derive integrals of the associated reduced maps.
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Takafumi Ogawa, Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta
2006 Volume 75 Issue 12 Pages
123501
Published: December 15, 2006
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By extensive Monte Carlo simulations, two separate peaks are found in the specific heat of relatively small spherical clusters of particles with 100≤
N≤400, interacting via the Yukawa and Coulomb potentials and confined in the external field. The analyses of the diffusion and positional fluctuations show that these peaks at lower and higher temperatures reflect the loss of intrashell two-dimensional ordering and of the radial ordering, respectively. The magnitudes of the fluctuations in the outermost shell are consistent with the conventional Lindemann criterion. The results can be verified by experiments in ion traps and in dusty plasmas under microgravity or equivalent isotropic environments.
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Yasuhiro Hatsugai
2006 Volume 75 Issue 12 Pages
123601
Published: December 15, 2006
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We propose the use of quantized Berry phases as a local topological order parameter of a gapped quantum liquid in any dimension that is invariant under some antiunitary operation. The Berry connection is constructed by the response of the quantum manybody state to a local perturbation. Due to the anti-unitary invariance, the Berry phases are quantized as 0 or π unless the energy gap closes by the local perturbation. Nontrivial characterizations are demonstrated for ground states of frustrated Heisenberg models and manybody ground states of half-filled random-hopping models. The local topological-order parameters in the models provide quantized texture patterns of local singlet pairs and fermionic local covalent bonds. The Haldane phase of the spin 1 chain is also characterized by the uniform π Berry phases.
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C. H. Lee, I. Hase, H. Sugawara, H. Yoshizawa, H. Sato
2006 Volume 75 Issue 12 Pages
123602
Published: December 15, 2006
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The phonon dynamics of filled skutterudite CeRu
4Sb
12 have been studied at room temperature by inelastic neutron scattering. Optical phonons associated with a large vibration of Ce atoms are observed at a relatively low energy of
E∼6 meV, and show anticrossing behavior with acoustic phonons. We propose that the origin of the low lattice thermal conductivity in filled skutterudites can be attributed to intensive Umklapp scattering originating from low-lying optical phonons. By an analysis based on a Born–von Kármán force model, the longitudinal force constants of the nearest Ce–Sb and Ce–Ru pairs are estimated to be 0.025 mdyn/Å, while that of the nearest Ru–Sb pair is estimated to be 1.4 mdyn/Å, indicating that the Ce atoms are bound very weakly to the surrounding rigid RuSb
6-octahedron cages.
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Hiroyuki Matsuzaki, Masahiro Yamashita, Hiroshi Okamoto
2006 Volume 75 Issue 12 Pages
123701
Published: December 15, 2006
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Photoconversion from a charge density wave (CDW) state to a Mott–Hubbard (MH) state in a one-dimensional (1D) extended Peierls–Hubbard system is observed by femtosecond (fs) reflection spectroscopy. The Br-bridged Pd compound examined is located near the CDW-MH phase boundary, and the irradiation of a fs laser pulse causes the instantaneous formation of a 1D MH domain without alternation of bridging-Br displacements. This result demonstrates the important role of intersite Coulomb repulsion in the transition, and in the stabilization of the CDW state. The formation of the MH domain is followed by a coherent oscillation with a period of 360 fs attributable to the relaxation of the bridging-Br displacements coupled with the charge-transfer between neighboring Pd ions.
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Hidekazu Mukuda, Machiko Abe, Sunao Shimizu, Yoshio Kitaoka, Akira Iyo ...
2006 Volume 75 Issue 12 Pages
123702
Published: December 15, 2006
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We report on superconducting (SC) characteristics for the oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba
2Ca
4Cu
5O
y [Cu-1245(OPT)], which includes pyramidal outer planes (OPs) and square inner planes (IPs). As a result of a reduction in the carrier density, the superconductivity for Cu-1245(OPT) occurs at the nearly optimally doped OPs with
Tc=98 K. The onset of static antiferromagnetic (AFM) order at IPs is evidenced from the observation of zero-field Cu NMR at low temperatures, although the SC transition at OPs emerges below
Tc=98 K. A disorder, which is actually mapped onto the underdoped IPs, is demonstrated to cause a quantum phase transition from AFM metal to insulating state in an underdoped regime. This finding reinforces that an AFM metallic phase exists between the AFM insulating phase and the SC phase for the ideally flat CuO
2 plane without disorder, as reported for the IPs in optimally doped Hg-1245 with the same doping level as in Cu-1245(OPT).
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Kozo Okada, Akio Kotani
2006 Volume 75 Issue 12 Pages
123703
Published: December 15, 2006
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We theoretically show that the oxygen 1
s x-ray photoelectron spectrum (O 1
s XPS) directly refelcts the unoccupied part of the electronic states of strongly correlated oxides. On the basis of numerically exact diagonalization calculations performed using a finite-size cluster model, we study the electron- or hole-doping dependence of the O 1
s XPS of two-dimensional copper compounds in detail. The O 1
s XPS has a weak charge-transfer (CT) satellite structure, which is located at about 10 eV above the main line. In this CT final state, an O 2
p valence electron ejected by the O 1
s core hole potential is transferred to the conduction states. Thus, the line shape of the CT satellite reflects the upper Hubbard band for electron-doped or undoped cuprates and also the Zhang–Rice singlet band for hole-doped cuprates.
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Chisa Hotta, Nobuo Furukawa, Akihiko Nakagawa, Kenn Kubo
2006 Volume 75 Issue 12 Pages
123704
Published: December 15, 2006
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The strong coupling phase diagram of spinless fermions on an anisotropic triangular lattice at half-filling is presented. The geometry of inter-site Coulomb interactions rules the phase diagram. Unconventional charge ordered phases are detected, which are the recently reported pinball liquid and the striped chain phases. Both are induced by the quantum dynamics out of classical disordered states and afford extremely correlated metallic states and a particular domain wall-type of excitations, respectively. The disorder once killed by the quantum effect revives at finite temperature, which is discussed in terms of the organic θ-ET
2X.
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H. Okabe, K. Suzuki, K. Kawashima, T. Muranaka, J. Akimitsu
2006 Volume 75 Issue 12 Pages
123705
Published: December 15, 2006
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We report here on the magnetic properties of Cu
2OCl
2, the structure of which can be regarded either as a pyrochlore-like corner-shared tetrahedral network with
S=1⁄2 or cross-linking chains of edge-sharing CuO
2Cl
2 squares. The magnetic susceptibility exhibits a broad maximum at approximately 140 K, indicating a low-dimensional feature, and drops at 70 K accompanied with a small specific-heat jump; however, it does not follow the typical
S=1⁄2 linear chain model. The magnetic susceptibility can be explained by a mean field corrected chain model with a closed value of the intra- and interchain exchange constants; thus, magnetic frustration would be dominant over a low-dimensional feature in Cu
2OCl
2. From the band calculation results, we found that the Cu 3
d on-site Coulomb interaction is essential to describe the electronic structure of Cu
2OCl
2. We conclude that Cu
2OCl
2 should be regarded as a 3D material that has the potential to combine the pyrochlore-like geometrical frustration and the strong correlation among the Cu 3
d electrons.
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Melike Abliz, Yoshiya Uwatoko, Takeo Ohki, Hironobu Fujii, Richard A S ...
2006 Volume 75 Issue 12 Pages
123706
Published: December 15, 2006
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Fe
2P is a well-known transition metal compound that shows a first-order ferromagnetic phase transition under 0–5 kbar of pressure. Here, the electrical resistivity has been investigated in the temperature interval of 2.5–300 K, employing a cubic anvil pressure cell up to 8 GPa. We found that two types of new phase transitions have occurred under pressures of 2 to 8 GPa. However, both new phases show that the transition temperatures increase with increasing pressure, and they are considered to be due to magnetic phase transitions with different dimensions such as two dimensional (2D) and three dimensional (3D) of Fe
2P, under pressure.
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Eiichi Matsuoka, Yuta Sasaki, Daichi Usui, Masaaki Nakagawa, Hideya On ...
2006 Volume 75 Issue 12 Pages
123707
Published: December 15, 2006
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We have examined the effects of Gd substitution on the anomalous antiferromagnetic (AFM) properties of TbB
2C
2 having field-induced antiferro-quadrupolar (AFQ) ordered phases. The Gd substitution induces drastic changes in the magnetic properties. The AFM structure characteristic to TbB
2C
2, the anomalous increase in magnetic susceptibility below
TN, and the strong preference of AFM domains disappear with the substitution of low Gd content of less than 10%. We propose a promising assumption that an antiferro-octupolar (AFO) ordering occurs at
TN simultaneously with AFM ordering in TbB
2C
2. The fragility of anomalous properties originates in the fragility of the antiferro-octupolar interaction against the substitution of Gd
3+ ions with
L=0.
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Allen Parker, Yoshimasa Matsuno
2006 Volume 75 Issue 12 Pages
124001
Published: December 15, 2006
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A method for obtaining peakon limits of multisoliton solutions of the Camassa–Holm equation is proposed and used to recover the peakon and two-peakon limits of the solitary wave and two-soliton solution, respectively. The limiting procedure is based on a novel representation of the soliton solutions — called
PQ-decomposition — that is introduced in the study. The results shed light on the interaction dynamics of the two-soliton: it is shown that any single-crested collision eventually breaks down into a double-humped soliton as we proceed to the peakon limit. A criterion is obtained that discriminates between this dynamical behaviour of the two-soliton solutions and, by extension, determines the breakdown point in the interaction. This can be viewed as a direct analogue of the classical result for the Korteweg–de Vries equation whereby a critical amplitude-ratio dictates whether a two-soliton forms a single- or double-peaked wave at collision.
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Seiji Miyoshi, Masato Okada
2006 Volume 75 Issue 12 Pages
124002
Published: December 15, 2006
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Conventional ensemble learning combines students in the space domain. In this paper, however, we combine students in the time domain and call it time-domain ensemble learning. We analyze, compare, and discuss the generalization performances regarding time-domain ensemble learning of both a linear model and a nonlinear model. Analyzing in the framework of online learning using a statistical mechanical method, we show the qualitatively different behaviors between the two models. In a linear model, the dynamical behaviors of the generalization error are monotonic. We analytically show that time-domain ensemble learning is twice as effective as conventional ensemble learning. Furthermore, the generalization error of a nonlinear model features nonmonotonic dynamical behaviors when the learning rate is small. We numerically show that the generalization performance can be improved remarkably by using this phenomenon and the divergence of students in the time domain.
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Fumitaka Tagawa, Takashi Odagaki
2006 Volume 75 Issue 12 Pages
124003
Published: December 15, 2006
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A theory for the nonlinear energy response of a system subjected to a heat bath is developed for the case in which the temperature of the heat bath is modulated sinusoidally. The theory is applied to a nonequilibrium system described by the free energy landscape picture. The following are shown (1) The ac specific heat is represented by the superposition of the Debye relaxations with different relaxation times, which correspond to eigenvalues of the transition rate matrix for the jump motion among basins in the landscape. (2) The 2nd-order energy response consists of two terms; oscillating and nonoscillating terms. The 2nd-order ac specific heat is defined for the first time from the oscillating term. (3) In the high-frequency limit, the 2nd-order ac specific heat and the nonoscillating term of the 2nd-order energy response are proportional to the 2nd temperature derivative of the transition rate. To show the validity of the formalism, a two-basin system is analyzed, where the barrier between two basins diverges at a certain temperature
T0. The 2nd-order ac specific heat has extrema as a function of the frequency, which diverges at
T0. A similar behavior appears in the high-frequency limit of the nonoscillating term of the 2nd-order energy response.
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Xiang-Yu Ge, Miki Wadati
2006 Volume 75 Issue 12 Pages
124004
Published: December 15, 2006
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The reflection equation algebra of Sklyanin is extended to the supersymmetric case. A graded reflection equation algebra is proposed and the corresponding graded (supersymmetric) boundary quantum inverse scattering method (QISM) is formulated. As an application, integrable open-boundary conditions for the doped spin-1 chain of the supersymmetric
t–
J model are studied in the framework of the boundary QISM. Diagonal boundary
K-matrices are found and four classes of integrable boundary terms are determined.
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Takafumi Kita
2006 Volume 75 Issue 12 Pages
124005
Published: December 15, 2006
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A statistical-mechanical investigation is performed on Rayleigh–Bénard convection of a dilute classical gas starting from the Boltzmann equation. We first present a microscopic derivation of basic hydrodynamic equations and an expression of entropy appropriate for the convection. This includes an alternative justification for the Oberbeck–Boussinesq approximation. We then calculate entropy change through the convective transition choosing mechanical quantities as independent variables. Above the critical Rayleigh number, the system is found to evolve from the heat-conducting uniform state towards the convective roll state with monotonic increase of entropy on the average. Thus, the principle of maximum entropy proposed for nonequilibrium steady states in a preceding paper [T. Kita: J. Phys. Soc. Jpn.
75 (2006) 114005] is indeed obeyed in this prototype example. The principle also provides a natural explanation for the enhancement of the Nusselt number in convection.
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Hidetsugu Sakaguchi
2006 Volume 75 Issue 12 Pages
124006
Published: December 15, 2006
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A generalized Einstein relation is studied for Brownian motion in a tilted potential. The exact form of the diffusion constant of the Brownian motion is compared with the generalized Einstein relation. The generalized Einstein relation is a good approximation in a parameter range where the Brownian motion exhibits stepwise motion.
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Ryosuke Hosaka, Yutaka Sakai, Tohru Ikeguchi, Shuji Yoshizawa
2006 Volume 75 Issue 12 Pages
124007
Published: December 15, 2006
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It was recently found that the leaky integrate-and-fire (LIF) model with the assumption of temporally uncorrelated inputs cannot account for the spiking characteristics of
in vivo cortical neurons. Specifically, the inter-spike interval (ISI) distributions of some cortical neurons are known to exhibit relatively large skewness to variation, whereas the LIF model cannot realize such statistics with any combination of model parameters. In the present paper, we show that the Bonhoeffer–van del Pol (BvP) model incorporating the same assumption of uncorrelated inputs can, by contrast, exhibit large skewness values. In this case, the large values of the skewness coefficient are caused by the mixture of widely distributed ISIs and short-and-constant ISIs induced by a sub-threshold oscillation peculiar to Class II neurons, such as the BvP neuron.
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Friedrich Everling
2006 Volume 75 Issue 12 Pages
124201
Published: December 15, 2006
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Binding energies of self-conjugate even–even nuclides are plotted as −
B*+(9.5MeV)·
A versus mass number
A, where
B* is the binding energy of ground states and levels. A diagram from
A=0 to 76 mainly for ground states shows a subshell systematics. In a diagram from
A=16 to 40, established and hypothetical 0
+ levels are shown; 24 states of supposed 1d
5⁄2, 2s
1⁄2, and 1d
3⁄2 subshell occupations are connected by almost linear trends. Surprisingly, early insufficient measurements at
Ex=0.65 MeV in
20Ne and 0.5 (and 0.43) MeV in
32S fit the trends. A diagram for the 0
+, 2
+, 4
+, and 6
+ band from
16O to
28Si suggests the 0
+ head in
20Ne to be at 0.65 MeV. A systematics of 2
+ states supports both levels. A plot of 3
− and 4
− states contains two pairs of nearly parallel and linear 3-point trends. A table suggests a total of 18 important experimental investigations.
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Masami Kawaguchi, Sukehiro Niga, Nobuaki Gou, Kazuo Miyake
2006 Volume 75 Issue 12 Pages
124401
Published: December 15, 2006
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The buoyancy-driven path instabilities of an air bubble rising in a Hele–Shaw cell are examined as a function of the ratio of the gravitational and the capillary forces, i.e., the Eötvös number (
Eo) of the bubble, for pure water, aqueous isopropyl alcohol (IPA) solutions, and aqueous hydroxypropyl methyl cellulose (HPMC) solutions. In the simple solutions, when
Eo exceeds a threshold value, the motion of the bubble center can be categorized into three regimes: (1) a zigzag path for small
Eo, (2) a straight path for intermediate
Eo, and (3) another zigzag path accompanied by changes in the bubble for larger
Eo; these transitions occur irrespective of the fluid we examined. For HPMC solutions with concentrations lower than 0.001 g/100 mL, three different trajectories—a damped vibrational motion without changes in the bubble shape, a straight trajectory, and another damped vibrational motion accompanied by changes in the bubble shape—are observed as
Eo increases. However, such path instabilities are suppressed for HPMC solutions with concentrations higher than 0.005 g/100 mL. Moreover, path instabilities occur when the Strouhal number exceeds a threshold of 0.2, which leads to the oscillation of the periphery length of the bubble for any of the solutions we studied.
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Daisuke Uematsu, Minoru Soda, Yoshiaki Kobayashi, Masatoshi Sato, Naok ...
2006 Volume 75 Issue 12 Pages
124601
Published: December 15, 2006
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For Ag
2Cu
2O
3, the close coupling of the crystal distortion to the magnetic ordering which takes place at 70 K has been found by X-ray and neutron diffraction analyses and magnetic measurements. The system has a pyrochlore-related structure with corner-sharing tetrahedra of Cu
2+ ions, in which the geometrical frustration is inherent. We show how the structural distortion releases the frustration, stabilizing the ordered state of Cu spins (
S=1⁄2). The magnetic susceptibility and specific heat of Ag
2Cu
2O
4 have also been measured. The results indicate that the system is nonmagnetic.
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Aki Yamane, Fuyuki Shimojo, Kozo Hoshino
2006 Volume 75 Issue 12 Pages
124602
Published: December 15, 2006
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We have carried out large-scale and long-time molecular-dynamics simulations for fluid mercury near the critical point using Lennard-Jones-type effective pair potential derived by the inverse method from the observed structure factor near the critical point. We have investigated the dependence of the structure on the system size and cut-off distance of the effective pair potential, and found that the static structure depends strongly on the system size and cut-off distance, when the system is close to the critical point. In particular, the long-wavelength density fluctuation increases drastically with increasing the cut-off distance of the potential near the critical point. Therefore very weak interatomic interaction at very long distance is important near the critical point. We have also obtained the critical exponents for the structure factor and the correlation length of the density fluctuation and shown that they approach the theoretical values when the system size and the cut-off distance increase.
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Masaki Kawamura, Masato Okada
2006 Volume 75 Issue 12 Pages
124603
Published: December 15, 2006
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We investigate dynamics of recurrent neural networks with correlated noise to analyze the noise’s effect. The mechanism of correlated firing has been analyzed in various models, but its functional roles have not been discussed in sufficient detail. Aoyagi and Aoki have shown that the state transition of a network is invoked by synchronous spikes. We introduce two types of noise to each neuron: thermal independent noise and correlated noise. Due to the effects of correlated noise, the correlation between neural inputs cannot be ignored, so the behavior of the network has sample dependence. We discuss two types of associative memory models: one with auto- and weak cross-correlation connections and one with hierarchically correlated patterns. The former is similar in structure to Aoyagi and Aoki’s model. We show that stochastic transition can be presented by correlated rather than thermal noise. In the latter, we show stochastic transition from a memory state to a mixture state using correlated noise. To analyze the stochastic transitions, we derive a macroscopic dynamic description as a recurrence relation form of a probability density function when the correlated noise exists. Computer simulations agree with theoretical results.
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Tsuneya Ando
2006 Volume 75 Issue 12 Pages
124701
Published: December 15, 2006
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The frequency shift and broadening of long-wavelength optical phonons due to interactions with electrons are calculated in a monolayer graphene as a function of the electron density. The broadening disappears and the frequency shift exhibits a logarithmic singularity when the Fermi energy is half of the energy of the optical phonon. The shift increases in proportion to the Fermi energy for sufficiently high electron density.
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Mamoru Yogi, Takayuki Nagai, Yojyu Imamura, Hidekazu Mukuda, Yoshio Ki ...
2006 Volume 75 Issue 12 Pages
124702
Published: December 15, 2006
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We report on the systematic evolution of normal-state properties and superconducting characteristics in filled-skutterudite compounds (Pr
1−xLa
x)Os
4Sb
12 determined using Sb nuclear-quadrupole-resonance (NQR) experiments. The Sb-NQR spectra in these compounds have split into two sets, arising from different Sb
12 cages containing either Pr or La, which enables us to measure two kinds of nuclear spin–lattice relaxation time
T1Pr and
T1La. In the normal state, the temperature (
T) dependence of 1⁄
T1PrT showed almost the same behavior as that for pure PrOs
4Sb
12 regardless of the increase in La content. In contrast, 1⁄
T1LaT markedly decreases with increasing La concentration. These results show that 4
f2-derived magnetic fluctuations are almost localized at the Pr site. In the superconducting state for Pr-rich compounds of
x=0.05 and 0.2, 1⁄
T1Pr exponentially decreases down to
T=0.7 K with no coherence peak below
Tc as well as in PrOs
4Sb
12. A remarkable finding is that the residual density of states (RDOS) at the Fermi level below
Tc is induced by La substitution for Pr. The impurity effect, usually observed in unconventional superconductors with a line–node gap, may not be the origin of the RDOS induced by the La substitution, since RDOS does not increase and
Tc does not decrease with increasing La content. RDOS is more naturally explained if a small part (∼5.5%) of the total Fermi surface (FS) becomes gapless for
x=0.05 and 0.2. These results are proposed to be understood in terms of a multiband-superconductivity (MBSC) model that assumes a full gap for part of the FS and the presence of point nodes for a small 4
f2-derived FS inherent in PrOs
4Sb
12. The former could be relevant with FS existing in LaOs
4Sb
12 and with the anisotropic gap with point nodes being markedly suppressed by either applying a magnetic field or substituting La for Pr. For La-rich compounds of
x=0.8 and 1, on the other hand, 1⁄
T1La exhibits a coherence peak and the nodeless energy gap characteristic for weak-coupling BCS
s-wave superconductors. With increasing Pr content,
Tc increases and the energy gap increases from 2Δ
0⁄
kBTc=3.45 for pure La compounds up to 2Δ
0⁄
kBTc=4.2 and 5.2 for the 60% Pr and 80% Pr compounds, respectively. The Pr substitution for La enhances the pairing interaction and induces an anisotropy in the energy-gap structure. The novel strong-coupling superconductivity in PrOs
4Sb
12 is inferred to be mediated by the local interaction between 4
f2-derived crystal-electric-field states with the electric quadrupole degree of freedom and conduction electrons. This coupling causes a mass enhancement of quasi-particles for a part of FS and induces a small FS, which is responsible for point nodes in the superconducting gap function. Note that the small FS does not play any primary role for the strong-coupling superconductivity in PrOs
4Sb
12.
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Yositake Takane
2006 Volume 75 Issue 12 Pages
124703
Published: December 15, 2006
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DC Josephson effect in a disordered wire with symplectic symmetry is studied based on a random-matrix approach. In a symplectic system, the Anderson localization disappears when the number
N of conducting channels is odd. Our attention is focused on a related anomaly arising in the temperature (
T) dependence of the Josephson critical current which is characterized by the thermal length ξ
T. We obtain ξ
T as a function of
T, and find an anomalous crossover from ξ
T=\\sqrt
D⁄2π
T in the high-temperature regime of
T>>
Tcross to ξ
T=
vF⁄(2π
NT) in the low-temperature regime of
T<<
Tcross, where
D and
vF are the diffusion constant and the Fermi velocity, respectively. The crossover temperature is given by
Tcross∼
D⁄ξ
2 with the conductance decay length ξ.
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Chitoshi Yasuda, Synge Todo, Hajime Takayama
2006 Volume 75 Issue 12 Pages
124704
Published: December 15, 2006
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Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of quantum Monte Carlo simulation. It is found that, when the ground state of the nondiluted system is a nonmagnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid-gap in the original spin gap, and under a strong bond dilution an antiferromagnetic long-range order emerges. While the site-dilution-induced long-range order is induced by an infinitesimal concentration of dilution, there exists a finite critical concentration in the case of bond dilution. We argue that this essential difference is due to the occurrence of two types of effective interactions between induced magnetic moments in the case of bond dilution, and that the antiferromagnetic long-range-ordered phase does not appear until the magnitudes of the two interactions become comparable.
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Salasa Nawang, Ichita Endo, Masataka Iinuma, Tohru Takahashi, Akitsugu ...
2006 Volume 75 Issue 12 Pages
124705
Published: December 15, 2006
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We performed a systematic study on Parametric X-ray radiation from a textured polycrystalline molybdenum target at a 150-MeV electron ring. The measurements were conducted at three observation angles (11.27, 25.89, and 179.85°). The spectral data shows that the spectrum has a unique characterestics: its peak energies depend mainly on the observation angles, its width is much wider than that with the monocrystal case, and its intensities are sometimes comparable to the charactestics Kα of Mo. The observed properties are related to the texture of the polycrystal.
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Shugo Ikeda, Hironori Sakai, Tatsuma D. Matsuda, Dai Aoki, Yoshiya Hom ...
2006 Volume 75 Issue 12 Pages
124706
Published: December 15, 2006
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The ferromagnet UTeS with the Curie temperature
TC=87 K has been studied by measuring the magnetization, magnetic susceptibility, electrical resistivity, magnetoresistance, Hall resistivity and specific heat. The magnetization was found to be highly anisotropic. The easy-axis was determined as the [001] direction, whereas the hard-axis magnetization for
H||[100] decreases below
TC, indicating an antiferromagnetic feature. The electrical resistivity also indicates a peak structure at
TC. These results suggest that UTeS is a canted ferromagnet. A large negative magnetoresistance was also observed around
TC. From the result of the Hall resistivity measurement, UTeS is thought to be a semimetal. This is consistent with the large value of the electrical resistivity and the small electronic specific heat coefficient.
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Yuichi Otsuka, Masatoshi Imada
2006 Volume 75 Issue 12 Pages
124707
Published: December 15, 2006
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We investigate the electronic structure of the transition-metal oxide YVO
3 by a hybrid first-principles scheme. The density-functional theory with the local-density-approximation by using the local muffin-tin orbital basis is applied to derive the whole band structure. The electron degrees of freedom far from the Fermi level are eliminated by a downfolding procedure leaving only the V 3
d t2g Wannier band as the low-energy degrees of freedom, for which a low-energy effective model is constructed. This low-energy effective Hamiltonian is solved exactly by the path-integral renormalization group method. It is shown that the ground state has the
G-type spin and the
C-type orbital ordering in agreement with experimental indications. The indirect charge gap is estimated to be around 0.7 eV, which prominently improves the previous estimates by other conventional methods.
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Yoshiyuki Nakagawa, Takanari Kashiwagi, Hironori Yamaguchi, Shojiro Ki ...
2006 Volume 75 Issue 12 Pages
124708
Published: December 15, 2006
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We report the results of electron spin resonance (ESR) and magnetization measurements in high magnetic fields up to about 52 T on single crystal and powder samples of the cobalt compound Na
2Co
2(C
2O
4)
3(H
2O)
2 which consists of two-leg ladders of Co
2+ ions. This compound was reported to be a candidate which show a signature of a quantum phase transition from a spin-liquid to a Néel ordered state [Z. Honda
et al.: Phys. Rev. Lett.
95 (2005) 087204]. From our ESR and magnetization experiments, we, however, have found that the compound is well described by almost isolated antiferromagnetic dimers which are formed by the nearest Co spins on the rungs and the interaction along the rung direction is much larger than that along the leg one. The ESR frequency–field diagram, magnetic susceptibility and magnetization are in good agreement with those calculated from this isolated dimer model.
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Yasuhiro Takayama, Tetsuo Yoshida, Satoshi Nakamura, Naoya Sasaki, Hir ...
2006 Volume 75 Issue 12 Pages
124709
Published: December 15, 2006
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We have measured the dependence of the magnetic circular dichroism (MCD) of the X-ray emission spectra (XES) on the temperature and incident angle for a Gd thin film. The energy of the incident photon for the XES was 138.25 eV, which corresponded to the resonant excitation to the
8D
9⁄2 intermediate state. The dependence of the observed MCD on the temperature and incident angle was quite different from that of the magnetic moment estimated with a SQUID magnetometer. By considering the reflection, saturation effect, self-absorption effect and magnetic anisotropy of the thin film, the agreement of the two behaviors was considerably improved. This result shows that the revisions of the MCD of the XES are extremely important for the quantitative estimation of the magnetic moment from the MCD of the XES.
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Kazutaka Kudo, Yoshiyuki Miyoshi, Takahiko Sasaki, Terukazu Nishizaki, ...
2006 Volume 75 Issue 12 Pages
124710
Published: December 15, 2006
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We report the out-of-plane resistivity of Bi
1.79Pb
0.37Sr
1.86CuO
6+δ single crystals with various doping levels in magnetic fields up to 15 T parallel to the
c-axis. By using the low-
Tc system sensitive to magnetic fields, two kinds of pseudogaps PG1 and PG2 are found at
T1* and
T2* below which the nonmetallic resistivity starts to develop and to be suppressed in magnetic fields with decreasing temperature, respectively. The doping dependence of
T2* exhibits a dome-like shape similar to
Tc, indicating the close relation between PG2 and the superconductivity, while
T1* decreases monotonically with increasing the doping level. Systematic hole-doping reveals that
T1* exists even in the heavily overdoped nonsuperconducting sample, indicating the weak relation between PG1 and the superconductivity.
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Takashi Hotta, Hisatomo Harima
2006 Volume 75 Issue 12 Pages
124711
Published: December 15, 2006
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We propose an effective model on the basis of a
j–
j coupling scheme to describe local
f-electron states for realistic values of Coulomb interaction
U and spin–orbit coupling λ, for future development of microscopic theory of magnetism and superconductivity in
fn-electron systems, where
n is the number of local
f electrons. The effective model is systematically constructed by including the effect of a crystalline electric field (CEF) potential in the perturbation expansion in terms of 1⁄λ. In this paper, we collect all the terms up to the first order of 1⁄λ. Solving the effective model, we show the results of the CEF states for each case of
n=2–5 with
Oh symmetry in comparison with those of the Stevens Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF energy levels in an intermediate coupling region with λ⁄
U in the order of 0.1 corresponding to actual
f-electron materials between the
LS and
j–
j coupling schemes. Note that the relevant energy scale of
U is the Hund’s rule interaction. It is found that the CEF energy levels in the intermediate coupling region can be quantitatively reproduced by our modified
j–
j coupling scheme, when we correctly take into account the corrections in the order of 1⁄λ in addition to the CEF terms and Coulomb interactions which remain in the limit of λ=∞. As an application of the modified
j–
j coupling scheme, we discuss the CEF energy levels of filled skutterudites with
Th symmetry.
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Kenichi Hachitani, Hideaki Amanuma, Hideto Fukazawa, Yoh Kohori, Keiic ...
2006 Volume 75 Issue 12 Pages
124712
Published: December 15, 2006
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The
31P-NMR (nuclear magnetic resonance) measurements of the filled skutterudite SmRu
4P
12 have been carried out in several applied magnetic fields. The line width of the
31P-NMR spectrum rapidly increases below the metal–insulator transition temperature
TMI, which indicates the appearance of an internal field below the temperature. Though no distinct anomaly was observed below
TMI in low fields, a complicated structure was observed between the Néel temperature
TN and
TMI (
TN<
TMI) above 70 kOe. The spin–lattice relaxation rate 1⁄
T1 is almost independent of temperature above
TMI, and rapidly decreases below
TMI. The 1⁄
T1 in low fields decreases monotonously, whereas the strong suppression of 1⁄
T1 occurs between
TN and
TMI above 70 kOe. The structure of the spectra and the suppression of 1⁄
T1 become apparent with increasing field.
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Wataru Higemoto, Yoshinori Haga, Tatsuma D. Matsuda, Yoshichika Onuki, ...
2006 Volume 75 Issue 12 Pages
124713
Published: December 15, 2006
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Superconducting and magnetic properties of the heavy fermion superconductor CePt
3Si were studied in a polycrystalline sample by means of the muon spin rotation and relaxation method. The muon Knight shift is invariant on passing the temperature through
Tc down to 20 mK at 17 kOe, indicating that the local spin susceptibility does not change in the superconducting state. The possible symmetry of superconductivity and the magnetic state in CePt
3Si are discussed.
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Y. Ihara, H. Takeya, K. Ishida, H. Ikeda, C. Michioka, K. Yoshimura, K ...
2006 Volume 75 Issue 12 Pages
124714
Published: December 15, 2006
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Co nuclear-quadrupole-resonance (NQR) measurements were performed on various bilayered hydrate cobaltate Na
x(H
3O)
zCoO
2·
yH
2O with different values of the superconducting and magnetic-ordering temperatures,
Tc and
TM, respectively. From measurements of the temperature and sample dependence of the NQR frequency, it was revealed that the NQR frequency is changed by the change of the electric field gradient (EFG) along the
c axis ν
zz rather than the asymmetry of EFG within the
ab-plane. In addition, it is considered that the change of ν
zz is gaverned mainly by the trigonal distortion of the CoO
2 block layers along the
c axis, from the relationships between ν
zz and the various physical parameters. We found the tendency that samples with ν
zz larger than 4.2 MHz show magnetic ordering, whereas samples with lower ν
zz show superconductivity. We measured the nuclear spin–lattice relaxation rate 1⁄
T1 in these samples, and found that magnetic fluctuations depend on samples. The higher-ν
zz sample has stronger magnetic fluctuations at
Tc. From the relationship between ν
zz and
Tc or
TM, we suggest that the NQR frequency can be regarded as a tuning parameter to determine the ground state of the system, and develop the phase diagram using ν
zz. This phase diagram shows that the highest-
Tc sample is located at the point where
TM is considered to be zero, which suggests that the superconductivity is induced by quantum critical fluctuations. We strongly advocate that the hydrate cobaltate superconductor presents an example of the magnetic-fluctuation-mediated superconductivity argued in the heavy-fermion compounds. The coexistence of superconductivity and magnetism observed in the sample with the highest ν
zz is also discussed on the basis of the results of our experiments.
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Youichi Yanase
2006 Volume 75 Issue 12 Pages
124715
Published: December 15, 2006
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We investigate the role of disorder on the superconducting (SC) fluctuation in short coherence length
d-wave superconductors. The particular intetest is focused on the disorder-induced microscopic inhomogeneity of SC fluctuation and its effect on the pseudogap phenomena. We formulate the self-consistent 1-loop order theory for the SC fluctuation in inhomogeneous systems and analyze the disordered
t–
t′–
V model. The SC correlation function, electronic DOS and the critical temperature are estimated. The SC fluctuation is localized like a nanoscale granular structure when the coherence length is short, namely the transition temperature is high. This is contrasted to the long coherence length superconductors where the order parameter is almost uniform in the microscopic scale. In the former case, the SC fluctuation is enhanced by the disorder in contrast to the Abrikosov–Gorkov theory. These results are consistent with the STM, NMR and transport measurements in high-
Tc cuprates and illuminate the essential role of the microscopic inhomogeneity. We calculate the spacial dependence of DOS around the single impurity and discuss the consistency with the NMR measurements.
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Keisuke Matsuda, Nobuo Furukawa, Yukitoshi Motome
2006 Volume 75 Issue 12 Pages
124716
Published: December 15, 2006
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We present our theoretical results on the electronic state in vanadium spinel oxide AlV
2O
4. The material is a mixed-valent system with the average valence V
2.5+, and V cations constitute a frustrated pyrochlore structure. It shows a structural transition at ∼700 K, leading to the formation of seven V-sites clusters—heptamers. We study the electronic state of the heptamer by explicitly taking account of orbital degree of freedom as well as electron correlations. We show that the ground state of the heptamer for realistic parameters becomes spin-singlet because of strong σ-type bonding states of
t2g orbitals. The temperature dependence of the magnetic susceptibility in experiments is naturally understood by this singlet formation in heptamers. Our results indicate that in AlV
2O
4 orbital physics is relevant to stabilize a cluster-type singlet state instead of a previously proposed charge-ordered state with valence skipping.
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Kenichi Hachitani, Hideto Fukazawa, Yoh Kohori, Isao Watanabe, Yuichi ...
2006 Volume 75 Issue 12 Pages
124717
Published: December 15, 2006
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The
31P-NMR (nuclear magnetic resonance) and μSR (muon spin relaxation) measurements on the filled skutterudite system SmFe
4P
12 have been carried out. The temperature
T dependence of the
31P-NMR spectra indicates the existence of the crystalline electric field effect splitting of the Sm
3+ (
J=5⁄2) multiplet into a ground state and an excited state of about 70 K. The spin–lattice relaxation rate 1⁄
T1 shows the typical behavior of the Kondo system, i.e., 1⁄
T1 is nearly
T independent above 30 K, and varies in proportion to
T (the Korringa behavior, 1⁄
T1∝
T) between 7.5 and 30 K. The
T dependence deviated from the Korringa behavior below 7.5 K, which is independent of
T in the applied magnetic field of 1 kOe, and suppressed strongly in higher fields. The behavior is explained as 1⁄
T1 is determined by ferromagnetic fluctuations of the uncovered Sm
3+ magnetic moments by conduction electrons. The μSR measurements in zero field show the appearance of a static internal field associated with the ferromagnetic order below 1.6 K.
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Yosuke Yoshimura
2006 Volume 75 Issue 12 Pages
124801
Published: December 15, 2006
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Solvent effects on molecular association in mixed fluids are studied with a simple model system, in which a pair of spherical molecules (solute) X are associated in a mixed fluid composed of spherical molecules A and B. The solvent molecules A and B behave as identical hard spheres except for the interaction with the solute molecule X; B interacts through the square-well potential with X, while A acts as the hard sphere. The solvent effect on the equilibrium constant is expressed by the statistics of the number of interactions (bond number BN) of the molecular associate X
2 with B molecules. The statistics of the BN distribution is expressed by a bivariate distribution function with respect to the singly-bonded and the doubly-bonded solvent molecule B. Rigorous relations are derived for the BN distribution in the mixture and in the single-component fluid composed of B. The BN distributions are evaluated for the hard-sphere fluid using Monte Carlo methods. The molecular association is promoted at low mole fractions of B through the fluctuation in the local composition. The fluctuation of the BN of the doubly-bonded molecules plays an important role in non-monotonic dependence of the association constant on the composition of fluid mixture.
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Makoto Soma, Hirohiko Sato
2006 Volume 75 Issue 12 Pages
124802
Published: December 15, 2006
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In order to control the dimensionality and the topology of the arrangement of magnetic Ru ions, NaCl-type lithium ruthenates have been investigated. Three types of lithium ruthenates, Li
3RuO
4, Li
2RuO
3, and cubic-Li
xRuO
1+x, were synthesized using a hydrothermal method. All of them have NaCl-type structure, but the arrangements of the cations, Li
+ and Ru
5+ (or Ru
4+), differ from each other. Li
3RuO
4 with one-dimensional zigzag chains of Ru ions undergoes an antiferromagnetic transition at 66 K and exhibits an irreversibile magnetism below 32 K, where the zero-field-cooled susceptibility differs from the field-cooled susceptibility. Li
2RuO
3 with a two-dimensional honeycomb network of Ru ions demonstrates a paramagnetism almost independent of temperature. A novel ruthenate cubic-Li
xRuO
1+x, in which Ru and Li randomly occupy the cation sites of NaCl lattice, undergoes a spin-glass transition at 10 K.
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Hiroshi Yaguchi, Keiichi Takizawa, Minoru Kawamura, Naoki Kikugawa, Yo ...
2006 Volume 75 Issue 12 Pages
125001
Published: December 15, 2006
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Taikan Harami, Yoshitaka Yoda, Mamoru Fujiwara
2006 Volume 75 Issue 12 Pages
125002
Published: December 15, 2006
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Shugo Ikeda, Miho Nakashima, Tatsuma D. Matsuda, Naoyuki Tateiwa, Etsu ...
2006 Volume 75 Issue 12 Pages
125003
Published: December 15, 2006
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Akira Oguri, A. C. Hewson
2006 Volume 75 Issue 12 Pages
128001
Published: December 15, 2006
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