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Sachiko Kitajima
2004 Volume 73 Issue 5 Pages
1093-1096
Published: May 15, 2004
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The dynamics of a quantum dense coding process is formulated and exactly solved on the basis of a boson detector model previously used to study decoherence processes. When classical information encoded in entangled states is transmitted through a quantum mechanical communication channel, an environment exerts quantum noise causing decoherence and disentanglement. Shannon’s mutual information and error probability function are obtained explicitly as functions of time.
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Rui-Feng Zhang, Bai-Xin Liu
2004 Volume 73 Issue 5 Pages
1097-1100
Published: May 15, 2004
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Taking into account the contribution of magnetic energy, the lattice stability curves, i.e., the correlation between lattice energy and valence electron number, of 3–5d transition metals are constructed, and the stable structures of the ferromagnetic elements of Fe, Co and Ni being bcc, hcp and fcc, respectively, are confirmed. On the basis of calculated lattice stabilities and after further consideration of the orbital energy contributed from the valence electrons, a calculation method is proposed for calculating the structural formation enthalpy of 3–5d transition metal alloys. It is shown that the proposed calculation method is able to predict the correct structure-composition correlation over an entire composition range of the alloy systems consisting of 3–5d transition metals,
e.g., in the Co–Ni, Ru–Rh and Ir–Os systems as representatives.
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Kaoru Mizuno, Kimihiko Morikawa, Satoshi Yamamoto, Masanori Kuga, Hiro ...
2004 Volume 73 Issue 5 Pages
1101-1102
Published: May 15, 2004
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The vacancy generation process in ultrahigh-purity aluminum single crystals with a low dislocation density was investigated by synchrotron radiation topography using a white X-ray beam. Some straight lines were observed in the topographs taken after temperature rose to 300°C from room temperature, and they were confirmed to be rows of successive small interstitial-type dislocation loops grown as vacancy sources. It was concluded that the thermal generation mechanism of vacancies in ultrahigh-purity aluminum single crystals with a low dislocation density consists of the following two steps. First, small interstitial loops are heterogeneously formed in the crystal lattice; second, these convert to lengthened loops with the development of screw components and finally grow into rows of dislocation loops emitting vacancies into the lattice.
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Sei Suzuki, Tatsuya Nakajima
2004 Volume 73 Issue 5 Pages
1103-1106
Published: May 15, 2004
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The quantum Monte-Carlo method is applied to two-dimensional electron systems under strong magnetic fields. The negative-sign problem induced by this method can be avoided for certain filling factors by making a sign-problem-free Hamiltonian approximating the Coulomb-interaction Hamiltonian well. Our techniques for obtaining the sign-problem-free Hamiltonian are described in detail. Calculated results for the sign-problem-free Hamiltonian are also reported for Landau level filling ν=1⁄3 and are compared with those for the Coulomb-interaction Hamiltonian.
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Akinori Tanaka
2004 Volume 73 Issue 5 Pages
1107-1110
Published: May 15, 2004
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We present a class of exactly solvable models of correlated electrons. The models are defined in any dimension
d and consist of electron-hopping terms and local attractive interactions between electrons. For each even number of electrons less than or equal to 1⁄(
d+1)-filling, we find the exact ground state in which all electrons form pairs of a certain type, and thus the models exhibit an electron-pair condensation.
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Yositake Takane
2004 Volume 73 Issue 5 Pages
1111-1114
Published: May 15, 2004
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DC Josephson current through a metallic carbon nanotube with
N conducting channels is studied at temperature
T when the potential range of scatterers is larger than the lattice constant. With increasing length of the carbon nanotube, its conductance approaches the quantized value
G0=4
e2⁄
h irrespective of
N. Our attention is focused on the
T-dependence of the Josephson critical current
Ic in this conductance-quantization regime. The thermal length ξ
T, which characterizes
Ic(
T), is calculated by combining the Matsubara technique and the random-matrix approach. It is shown that ξ
T=h
vF⁄(2π
NkBT) (
vF: the Fermi velocity). This indicates that
Ic(
T) depends on
N, in contrast to the conductance which is given by
G0 irrespective of
N.
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Akito Kobayashi, Yasuhiro Tanaka, Masao Ogata, Yoshikazu Suzumura
2004 Volume 73 Issue 5 Pages
1115-1118
Published: May 15, 2004
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We investigate superconducting (SC) states in a two-dimensional extended Hubbard model at quarter-filling with on-site repulsive interaction (
U) and nearest-neighbor repulsive interaction (
V), which lead to spin fluctuation and charge fluctuation, respectively. The effect of charge fluctuation on the onset of the SC state is estimated by calculating pairing interaction within the random phase approximation. Solving a linearized Eliashberg equation with an anomalous self-energy as a function of both momentum and frequency, we examine the stability of a singlet SC state in a phase diagram of
U and
V with fixed temperatures. We obtain a novel result that the obtained SC state has
dxy symmetry in the vicinity of both spin density wave (SDW) phase (
U\\gtrsim
V) and charge density wave (CDW) phase (
V\\gtrsim
U). The CDW-SC and SC-metal phase boundaries exhibit reentrant structures on the
V–
T (temperature) plane.
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Hisatoshi Yokoyama, Yukio Tanaka, Masao Ogata, Hiroki Tsuchiura
2004 Volume 73 Issue 5 Pages
1119-1122
Published: May 15, 2004
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Superconductivity in the Hubbard model on a square lattice near half filling is studied using an optimization (or correlated) variational Monte Carlo method. Second-order processes of a strong-coupling expansion are considered in wave functions beyond the Gutzwiller projection. Superconductivity of d
x2−y2-wave symmetry is widely stable, and exhibits a crossover around
U=
Uco∼12
t from a BCS type to a new type. For
U\\gtrsim
Uco (
U\\lesssim
Uco), the energy gain in the superconducting state is derived from the kinetic (potential) energy. Condensation energy is large and ∝exp(−
t⁄
J) [tiny] on the strong [weak] coupling side of
Uco. With reference to experiments on optical conductivity, cuprates belong to the strong-coupling regime.
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Nao Takeshita, Takao Sasagawa, Takenari Sugioka, Yoshinori Tokura, Hid ...
2004 Volume 73 Issue 5 Pages
1123-1126
Published: May 15, 2004
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The effect of uniaxial pressure on superconductivity was examined for high-
Tc cuprate La
1.64Eu
0.2Sr
0.16CuO
4, which is located at the boundary between the superconducting and stripe phases. We found markedly large anisotropy of the uniaxial pressure effect not only between the in-plane and out-of-plane pressures but also
within the tetragonal CuO2 plane. When the pressure is applied along the [110] direction, we found the largest pressure effect ever observed in cuprates,
dTc⁄
dP[110]∼2.5 K/kbar, while the change in
Tc was not appreciable when the pressure is applied along [100]. This substantial in-plane anisotropy is attributed to an intimate link between the symmetry of one-dimensional stripes and that of the strain produced within the CuO
2 plane.
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Yunori Nisikawa, Hiroaki Ikeda, Kosaku Yamada
2004 Volume 73 Issue 5 Pages
1127-1130
Published: May 15, 2004
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To discuss the possibility that the superconductivities in Na
xCoO
2·
yH
2O are induced by electron correlation, we investigate the possible pairing symmetry based on the single-band Hubbard model whose dispersion of the bare energy band is obtained using the band structure calculation of Na
xCoO
2·
yH
2O. The superconducting transition temperature is estimated by solving the Éliashberg equation. In this equation, both normal and anomalous self-energies are calculated up to the third-order terms with respect to the Coulomb repulsion. In the case of spin-singlet pairing, the candidate of pairing symmetry (the maximum eigen value λ
maxSS of Éliashberg’s equation) belongs to the
d-wave (E
2 representation of D
6 group). In the case of spin-triplet pairing, the candidate of pairing symmetry (the maximum eigen value λ
maxST of Éliashberg’s equation) belongs to the
fy(y2−3x2)-wave (B
1 representation of D
6 group). It is found that λ
maxSS\\simeqλ
maxST and the transition temperatures of unconventional pairing state are estimated to be low compared with the observed temperature within our simple model.
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Takahiko Sasaki, Petre Badica, Naoki Yoneyama, Kazuyoshi Yamada, Kazum ...
2004 Volume 73 Issue 5 Pages
1131-1134
Published: May 15, 2004
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We report the in-plane resistivity and magnetic susceptibility of the layered cobalt oxide Na
0.35CoO
2·1.3H
2O single crystal. The temperature dependence of the resistivity shows metallic behavior from room temperature to the superconducting transition temperature
Tc of 4.5 K. A sharp resistive transition, zero resistivity and almost perfect superconducting volume fraction below
Tc indicate the good quality and bulk superconductivity of the single crystal. The upper critical field
Hc2 and coherence length ξ are obtained from the resistive transitions in the magnetic fields parallel to the
c-axis and
ab-plane. The anisotropy of ξ, ξ
ab⁄ξ
c=12nm⁄1.3nm\\simeq9.2, suggests that this material is an anisotropic three-dimensional superconductor. In the field parallel to the
ab-plane,
Hc2 seems to be suppressed to the Pauli paramagnetic limit. This suggests spin singlet superconductivity in the cobalt oxide.
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Masashige Matsumoto, Mikito Koga
2004 Volume 73 Issue 5 Pages
1135-1138
Published: May 15, 2004
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The most important character of the exotic superconductor PrOs
4Sb
12 is the existence of low-lying excitations (excitons) with a finite energy gap and it appears as the magnetic field-induced order above 4.5 T. We focus on the
au conduction band, which hybridizes with a Pr 4
f2 state strongly, coupled to the excitons. It results in an attractive interaction between the conduction electrons. The symmetry of the superconducting order parameter is determined by dispersion relation of the exciton. For the bcc system PrOs
4Sb
12, a
d-wave state (
kxky+ω
kykz+ω
2kzkx, ω=
e±i2π⁄3) is stabilized with broken time reversal symmetry.
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Yoshiaki Uesu, Ryuhei Nakai, Jean-Michel Kiat, Carole Ménoret, ...
2004 Volume 73 Issue 5 Pages
1139-1142
Published: May 15, 2004
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Optical second-harmonic generation (SHG) in SrTi
16O
3 (STO16) and SrTi
18O
3 (STO18) was investigated using the SHG microscope. While no biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36 K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, or STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar order, the combined studies reveal that the long-range order of the polar phase does not develop on either crystal and is frozen in local regions.
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Haruo Abe, Hiroshi Wako
2004 Volume 73 Issue 5 Pages
1143-1146
Published: May 15, 2004
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A statistical mechanical model for protein folding is applied to the three-dimensional lattice protein using a foldable amino acid sequence. The key to the model lies in the concept of its local structure, defined as a continuous region which takes the same local conformation as in the native conformation, and in the assumption of the absence of interactions between local structures. The partition function is precisely calculated for a given native conformation without any adjustable parameters. The model can well reproduce the equilibrium thermodynamic quantities obtained from the simulation.
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H. Keubou Nguena, S. Noubissie, P. Woafo
2004 Volume 73 Issue 5 Pages
1147-1150
Published: May 15, 2004
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The attenuation of waves is due to dissipative effects of the medium in which they travel. We study waves amplification in a nonlinear transmission line by doping the line with negative nonlinear resistance. Modifying the cells of the line with this resistance, the propagation of waves is governed by a perturbed Korteveg–de Vries (KdV) equation. Analytical results and numerical simulation show that the attenuated wave recovers its amplitude on a short distance of the doped domain. It is also shown that the wave conserves its pulse form when crossing the amplification domain.
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Hui-Hui Dai, Debin Huang, Zengrong Liu
2004 Volume 73 Issue 5 Pages
1151-1155
Published: May 15, 2004
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Many physical problems are governed by certain systems of singular ordinary differential equations (ODEs). As a result, singular solutions can arise. In this paper, we provide some theoretical results to deal with these solutions. By applying straightforwardly the notion of weak solutions for partial differential equations (PDEs), a notion of weak solutions for this ODE type is proposed to include these singular solutions. As an application, we consider some traveling-wave solutions of a nonlinear dispersion equation arising in a physical problem. It is shown that compactons can arise in nonlinear elastic rods.
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Yan-ze Peng
2004 Volume 73 Issue 5 Pages
1156-1158
Published: May 15, 2004
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The extended mapping method is proposed to obtain new exact solutions to a new Hamiltonian amplitude equation introduced by Wadati
et al. [J. Phys. Soc. Jpn.
61 (1992) 1187]. The new periodic wave solutions are the linear combination of two Jacobi elliptic waves. Limit cases are studied, and new solitary wave solutions and triangular periodic wave solutions are got.
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Jun-Xiao Zhao, Chun-Xia Li, Xing-Biao Hu
2004 Volume 73 Issue 5 Pages
1159-1163
Published: May 15, 2004
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We present an integrable coupled differential-difference Kadomtsev–Peviashvili equation, which is derived by extending Ohta and Hirota’s Pfaffianization procedure to the differential-difference KP equation. Some Lie symmetries of this resulting system are also presented explicitly.
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Shigetoshi Ohta
2004 Volume 73 Issue 5 Pages
1164-1170
Published: May 15, 2004
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We numerically study three-dimensional cellular structure by using the vertex model. We adopt a new triangulation method of cellular surface (model S), and compare it with two models (model N and model G). We find that they show similar scaling properties. Average face numbers of a cell are 13.92, 13.52, and 13.83 for model S, N, and G, respectively. We analytically obtain the lifetime of one regular polyhedral cell for each model. The distribution function of vertex velocity becomes a form of the log normal distribution. The vertex aberration from a flat cellular face is also investigated.
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Go Kato, Miki Wadati
2004 Volume 73 Issue 5 Pages
1171-1179
Published: May 15, 2004
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Presented is a method, which we call Bethe ansatz cluster expansion (BACE) method, to investigate statistical mechanics of quantum integrable systems. By use of only the Bethe ansatz equation,
n-particle partition functions are exactly calculated. From the expression for the partition function, the
n-particle cluster integrals are derived. The results completely agree with those of the thermal Bethe ansatz (TBA) by Yang and Yang. Thus, the BACE method directly proves the validity of the TBA. Partition theory and graphical representation are used to make the presentation simple and transparent.
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Shuifa Shen, Yan Li, Wenda Huang, Shuanghui Shi, Jiahui Gu, Jingyi Liu ...
2004 Volume 73 Issue 5 Pages
1180-1190
Published: May 15, 2004
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The decay of
76Br has been investigated by means of γ-ray spectroscopy. The
76Br nuclei were produced in two reactions, i.e.,
75As(α,3n)
76Br and
76Se(p,n)
76Br. The Compton-suppressed spectrometer and High-purity Ge detectors have been used singly and in coincidence, respectively, to study γ-rays in the β
++EC decay of
76Br to
76Se. 37 γ rays were observed for the first time among 138 γ-rays reported. A decay scheme of
76Br including 15 new levels is proposed which accommodates 120 of these transitions. Spins and parities for new levels are proposed from calculated log
ft 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 level scheme were compared with results from calculations in the framework of the projected shell model.
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Ali Maghari, Amir Hossain Jalili
2004 Volume 73 Issue 5 Pages
1191-1196
Published: May 15, 2004
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Viscosities, diffusion coefficients and thermal diffusion factors for CH
4–N
2 and CH
4–O
2 are determined from the extended law of corresponding states for viscosity and the experimental second virial coefficient data by an iterative inversion method. The Lennard-Jones (12,6) potential energy function is used as the initial model potential required the technique. The obtained effective interaction potentials reproduce viscosity, diffusion and thermal diffusion factor within experimental accuracies.
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Mehrdad Khanpour, G. A. Parsafar, B. Najafi
2004 Volume 73 Issue 5 Pages
1197-1204
Published: May 15, 2004
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We present in this paper a general analytical solution to the integral equations of liquid state theories (Born–Green–Yvon, hyper-netted-chain, and Percus–Yevick Equations) at low-density limit for potentials with a hard core. For the specific case of the Lennard-Jones potential with a hard core, we have derived an analytical function for the radial distribution function at high temperature and low density. We have noted that this function has two humps which is the characteristic feature of the radial distribution function at low densities. In addition, this function has been used to calculate the third virial coefficient for such a fluid exactly. We see that for the especial case of Lennard-Jones fluid with a hard core, which its radial distribution function has explicitly been calculated at high temperatures, the correct behavior of the third virial coefficient with temperature is obtained. The magnitude of hard-core diameter has significant effect on the thermodynamic properties of fluid: for instance, when the diameter changes only by a few percent the third virial coefficient may change more than 100%. The hard-core diameter decreases when temperature increases. The reduction is less than 20%. For the supercritical fluid, the calculated compression factor and internal energy are in good agreement with those obtained from the simulation for the Lennard-Jones fluid.
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K. Masuda-Jindo, Vu Van Hang
2004 Volume 73 Issue 5 Pages
1205-1215
Published: May 15, 2004
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Using the lattice Green’s function approach which includes the temperature dependence of the materials parameters, we study the both cleavage and dislocation emission processes in the fracture of crystalline materials. Firstly, we calculate the Green’s function for the defective lattice, with dislocation and crack, by solving the Dyson equation. After the lattice Green’s functions have been determined, the relaxation problem for the reconstituted bonds in the cohesive zone is solved. The external force
F with tensile and shear components is applied, as a pair of forces, to the atoms at the center of the crack. In this lattice Green’s function calculation the temperature effects resulting from the anharmonicity of lattice vibrations are included by introducing the thermal lattice expansion, temperature dependent force constant matrix and temperature dependent non-linear cohesive forces at the crack tip region. We compare the cleavage and dislocation emission processes at the absolute zero temperature with those of the higher temperatures.
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Yositaka Onodera
2004 Volume 73 Issue 5 Pages
1216-1221
Published: May 15, 2004
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The author’s earlier work on dynamical response of ferroelectrics [Prog. Theor. Phys.
44 (1970) 1477] is extended to incorporate relaxational response into the anharmonic-oscillator model. Dynamical polarizability of an oscillator in a double-minimum potential inevitably possesses a vanishing imaginary component proportional to
iωδ(ω) because of the non-ergodicity of its motion. When the oscillator is allowed to hop between the two minima through thermal contact with the reservoir, the above delta-function will acquire a broadening with characteristic hopping frequency. The resulting formula properly describes coexistence of soft modes and relaxational modes. It is thus explicitly shown that the unified model of ferroelectricity covers from the extreme limit of displacive ferroelectrics where only soft modes appear to the other limit of order–disorder ones where only Debye-type relaxation is observed.
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X. D. Dai, H. R. Gong, B. X. Liu
2004 Volume 73 Issue 5 Pages
1222-1227
Published: May 15, 2004
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Based on the cohesive energies and lattice constants of a few possible non-equilibrium Ag–Mo compounds obtained by
ab initio calculation, a Finnis–Sinclair (FS) potential of the equilibrium immiscible Ag–Mo system is derived. Applying the proven realistic potential, molecular dynamics simulation is carried out to study, at an atomic scale, the structural stability of the Ag-based solid solutions. The simulation results predict that the fcc crystalline structure can be preserved until the Mo concentration reaches 13 at.% and the correlation of the lattice constant of the Ag-based solid solutions vs the Mo concentration is in good agreement with Vegard’s Law. In addition, the heats of formation of the fcc Ag–Mo solid solutions calculated by the derived potential are quite agreeable with that calculated by Miedema’s theory.
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Katsurou Hanzawa
2004 Volume 73 Issue 5 Pages
1228-1236
Published: May 15, 2004
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In order to determine a proper RKKY interaction model for CeB
6, the general model Hamiltonian for Γ
8 quartet with nearest-neighbor interactions is investigated in terms of the constant coupling approximation (CCA). In contrast with the mean field approximation, any antiferro multipolar ordering becomes unstable near SU(4) symmetry due to fluctuation of interactions taken into account in the CCA as pair correlations. A semiquantitative explanation of the antiferro-quadrupolar transition temperature and the specific heat in phase I of CeB
6 is obtained in a case that the coupling constants of interactions between various moments are quite different each other. It is therefore possible that an RKKY interaction model proper for CeB
6 deviates considerably from SU(4) symmetry.
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Tadeusz Luty, Kenji Yonemitsu
2004 Volume 73 Issue 5 Pages
1237-1243
Published: May 15, 2004
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We study energetics of a cooperative low-spin (L) to high-spin (H) transformation in a crystal with two sublattices, where thermo- and photo-induced symmetry-broken phases have been recently observed. The model takes into account an intra-dimer antiferromatic coupling and inter-dimer couplings. Cooperative activation processes for switching between LH and HL states and that from LL to HH states of a dimer are analyzed. It is shown that locally (within a dimer) preferred symmetry-broken, LH and HL, states compete with inter-dimer couplings, which stimulates dynamical disorder via a decrease in the energy barrier for a flip between asymmetric configurations. On the other hand, a locally non-preferred symmetric state (HH) is supported by inter-dimer interaction via a cooperative activation mechanism. We conclude that symmetry-broken states can form an intermediate thermo-induced phase or can be observed as a photo-induced one at low temperatures as a result of local equilibrium. The global equilibrium follows from cooperative interaction and governs the thermo-induced re-entrant phase transition.
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Mitsuo Kataoka
2004 Volume 73 Issue 5 Pages
1244-1250
Published: May 15, 2004
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In order to get a realistic view of the origin of the antiferroorbital (AFO) order in LaMnO
3, MnF
3 and KCuF
3, both the cooperative Jahn–Teller effect (CJTE) and the orbital-dependent exchange interaction (OEI) are taken into account for the
dγ electron–lattice system in compounds with the perovskite-type structure. The phonon-mediated orbital interaction in the CJTE and the
dγ electron-mediated one in the OEI are treated by use of the mean-field approximation with preserving the symmetry of the crystal, and are joined to give an effective Hamiltonian. It is stressed that the CJTE favors any of the FO and AFO orders, while the OEI does only the AFO order. The present theory is consistent with the observed fact that the AFO order is characterized by an arrangement of alternate mixed orbitals of
dx2−y2 and
d3z2−r2, the AFO phase survives even at sufficiently high temperatures in the paramagnetic phase, and the AFO order is always accompanied by the ferrodistortion and the antiferrodistortion.
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Shinji Watanabe, Masatoshi Imada
2004 Volume 73 Issue 5 Pages
1251-1266
Published: May 15, 2004
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A new numerical algorithm for interacting fermion systems to treat the grand-canonical ensemble is proposed and examined by extending the path-integral renormalization group method. To treat the grand-canonical ensemble, the particle–hole transformation is applied to the Hamiltonian and basis states. In the interaction-term projection, the Stratonovich–Hubbard transformation which hybridizes up and down spin electrons is introduced. By using this method, the phase diagram of the two-dimensional Hubbard model with next-nearest-neighbor transfer is accurately determined by treating the filling-control (FC) and bandwidth-control (BC) Mott transitions on the same ground. A V-shaped Mott insulating phase is obtained in the plane of the chemical potential and the Coulomb interaction, where the transitions at the corner (BC) and the edges (FC) show contrasted characters with large critical fluctuations near the edges coexisting with the first-order transition at the corner. This contrasted behavior is shown to be consistent with the V-shape structure of the phase boundary because of a general relation, in which the slope of the metal–insulator transition line in the phase diagram is expressed by thermodynamic quantities. The V-shaped opening of the Mott gap is favorably compared with the experimental results of the transition metal oxides.
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Yukikuni Akishige, Youichi Yamazaki, Nobuo Môri
2004 Volume 73 Issue 5 Pages
1267-1272
Published: May 15, 2004
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The dc electrical resistivity ρ in the reduced hexagonal BaTiO
2.98 single crystal was measured under hydrostatic pressures up to 3.1 GPa in the temperature range of 5 K to 300 K. The ρ along the hexagonal
c axis is somewhat larger than that of the perpendicular direction. The ρ vs
T curve changes the behavior at the temperature
T0, where the hexagonal to orthorhombic phase transition takes place: it behaves as a semiconductor and a metal at temperatures below and above
T0, respectively. With increasing pressure
T0 decreases, and the metallic behavior dominates whole of the temperature range at pressures above
pc=1.9 GPa. In the pressure-induced metallic phase,
T2-dependence of resistivity appears at low temperatures. This rule suggests that electrons in the Ti 3
d band of BaTiO
3 are the same as electrons in a strongly correlated electron system. A band model is proposed to explain such insulator–metal transitions in SrTiO
3, cubic BaTiO
3, and hexagonal BaTiO
3.
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Tsuneya Ando
2004 Volume 73 Issue 5 Pages
1273-1280
Published: May 15, 2004
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Numerical calculations of the conductance are performed to study effects of a weak magnetic field or flux on a perfectly conducting channel in metallic carbon nanotubes in the presence of scatterers with potential range larger than the lattice constant. The perfect channel can easily be destroyed even by a very small magnetic field or flux when there are several bands at the energy, while it is much more robust in the energy range of metallic linear bands.
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Muneyuki Tsuda, Wilson Agerico Diño, Hiroshi Nakanishi, Hideaki ...
2004 Volume 73 Issue 5 Pages
1281-1284
Published: May 15, 2004
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To investigate cyclohexane dehydrogenation by a transition metal M (M: Pt, Pd, Ni and Cu) atom, we perform total energy calculations, based on the density functional theory. We consider the process where cyclohexane approaches the M atom. Upon interacting with the M atom, the M atom draws an H atom from the cyclohexane, forming an H–M bond. With a broken C–H bond, the dehydrogenated cyclohexane separates from the M atom. Of the M elements we investigated, a Pt atom exhibited the highest reactivity. In breaking the C–H bond of the cyclohexane, the σ donation dominates for a Pd and Cu atom as compared with the Pt atom, and the π back-donation dominates for a Ni atom as compared with the Pt atom. The results indicate that the excess charge transfer requires more energy for breaking the C–H bond of the cyclohexane with the Pd, Ni and Cu atom.
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Kazunori Tanaka, Hiroaki Ikeda, Kosaku Yamada
2004 Volume 73 Issue 5 Pages
1285-1289
Published: May 15, 2004
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Recently, superconductivity in PuCoGa
5 was discovered. It has the same crystal structure as Ce
MIn
5 (
M=Ir, Co, Rh), which are often refered to as Ce-115’s. The electron correlation in PuCoGa
5 is estimated to be weak compared with Ce-115’s, and the filling number of electrons is considered to be far from 0.5/spin in the band which plays an important role in realizing the superconductivity. Nevertheless, the superconducting transition temperature
Tc in PuCoGa
5 is almost by an order of magnitude higher than that in Ce-115’s. In order to explain the superconductivity with high
Tc, we adopt the periodic Anderson model and calculate
Tc by solving the Dyson–Gor’kov equation derived by the third order perturbation theory with respect to
U. By this calculation, we indicate that the superconducting state of PuCoGa
5 is a
d-wave pairing state, and show that the good location of two Fermi surfaces results in the high
Tc in PuCoGa
5.
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Naoki Yoneyama, Akihiro Higashihara, Takahiko Sasaki, Tsutomu Nojima, ...
2004 Volume 73 Issue 5 Pages
1290-1296
Published: May 15, 2004
Released on J-STAGE: July 25, 2007
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We report the in-plane penetration depth λ
|| of single crystals κ-(BEDT-TTF)
2X (
X=Cu(NCS)
2 and Cu[N(CN)
2]Br) by means of the reversible magnetization measurements under the control of cooling-rate. In
X=Cu(NCS)
2, λ
||(0) obtained by an extrapolation toward
T=0 K does not change by cooling-rate within the experimental accuracy, while
Tc is slightly reduced. On the other hand, in
X=Cu[N(CN)
2]Br, λ
||(0) indicates a distinct increase by cooling faster. The different behavior of λ
||(0) on cooling-rate between the two salts is quantitatively explained in terms of the local-clean approximation (the London model), considering that the former salt belongs to the very clean system and the latter the moderate clean one. The good agreement with this model demonstrates that disorders of the ethylene-group in BEDT-TTF introduced by cooling faster increase the electron(quasiparticle)-scattering, resulting in shorter mean free path.
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M. Yokoi, H. Watanabe, Y. Mori, T. Moyoshi, Y. Kobayashi, M. Sato
2004 Volume 73 Issue 5 Pages
1297-1302
Published: May 15, 2004
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Superconducting transition temperature
Tc of Na
zCo
1−xMxO
2·
yH
2O has been studied for
M=Ir and Ga, which can substitute for Co. It has been found that
Tc is suppressed by the M-atom doping. The decreasing rates |
dTc⁄
dx| are of the order of 1 K/% and too small to be explained by the pair breaking mechanism for the anisotropic order parameters by non-magnetic impurities. Brief arguments are given on possible origins of the
Tc suppression.
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Young-Chong Hsue, Tzong-Jer Yang, Ben-Yuan Gu, Jian Wang
2004 Volume 73 Issue 5 Pages
1303-1312
Published: May 15, 2004
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We present numerical studies of conductance of quasi-particles (QPs) in junctions consisting of semiconductor (Sm) two-dimensional electronic gas (2DEG) and superconductor (S) containing a finite width 2DEG region (referred to magnetic barrier) applied by a magnetic field perpendicular to the 2DEG plane. Total conductance as a function of β=μ
N⁄hω
c (where μ
N is the chemical potential of semiconductor and ω
c=
eB⁄
cm*N is the cyclotron frequency) strongly depends on the normal or superconducting state of the superconductor. It demonstrates that the Andreev reflection (AR) plays a dominant role. The total conductance of
G(NBN) or
G(NBS) as a function of β for the NBN or NBS junction displays monotonically increasing behavior with different rising slopes. We observe the existence of a critical magnetic field for switching off the conductance. This critical field of
G(NBS) is a half of that of
G(NBN) in the matching case of the Fermi level and effective mass of QPs in materials forming the junctions.
G(NBS) is usually larger than
G(NBN) for a given magnetic field. The 3D plot of the conductance
G(NBN) and
G(NBS) as functions of β and the incident angle θ of the QPs displays a flat plateau over a finite domain region of [β,θ]. However, in the mismatching case of the Fermi energy and effective mass of QPs,
G(NBS) is lower than
G(NBN) because the AR of the holelike QPs now becomes incomplete and normal reflection (NR) of the electronlike QPs is considerably enhanced. The corresponding 3D plot of conductance against β and θ exhibits heavy spike oscillations around its occupied boundary. We present explicit analytic expressions of the conductance of QPs for this model junction on the basis of classical cyclotron orbit of the QPs in magnetic fields and the quantum mechanical calculation. The characteristics of conductance can be well interpreted by this phenomenological physical picture.
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K. Deguchi, Z. Q. Mao, Y. Maeno
2004 Volume 73 Issue 5 Pages
1313-1321
Published: May 15, 2004
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We have obtained strong experimental evidence for the full determination of the superconducting gap structure in all three bands of the spin-triplet superconductor Sr
2RuO
4 for the first time. We have extended the measurements of the field-orientation dependent specific heat to include conical field rotations consisting of in-plane azimuthal angle φ-sweeps at various polar angles θ performed down to 0.1 K. Clear 4-fold oscillations of the specific heat and a rapid suppression of it by changing θ are explained only by a compensation from two types of bands with anti-phase gap anisotropies with each other. The results indicate that the active band, responsible for the superconducting instability, is the γ-band with the lines of gap minima along the [100] directions, and the passive band is the α- and β-bands with the lines of gap minima or zeros along the [110] directions in their induced superconducting gaps. We also demonstrated the scaling of the specific heat for the field in the
c-direction, which supports the line-node-like gap structures running along the
kz direction.
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Shin-Ichi Ikeda, Naoki Shirakawa, Takashi Yanagisawa, Yoshiyuki Yoshid ...
2004 Volume 73 Issue 5 Pages
1322-1325
Published: May 15, 2004
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We report a uniaxial pressure-dependence of magnetism in layered perovskite strontium ruthenate Sr
3Ru
2O
7. By applying a relatively small uniaxial pressure, greater than 0.1 GPa normal to the RuO
2 layer, ferromagnetic ordering manifests below 80 K from the enhanced-paramagnet. Magnetization at 1 kOe and 2 K becomes 100 times larger than that under ambient condition. Uniaxial pressure dependence of Curie temperature
TC suggests the first order magnetic transition. Origin of this uniaxial-pressure induced ferromagnetism is discussed in terms of the rotation of RuO
6 octahedra within the RuO
2 plane.
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Mitsuo Kataoka
2004 Volume 73 Issue 5 Pages
1326-1333
Published: May 15, 2004
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The appearance of the
A-type antiferrospin (
A-AFS) order under the antiferroorbital (AFO) order observed in some perovskite-like compounds is studied theoretically to resolve discrepancies between existing theories and to clarify its mechanism in an open way. The various kinetic exchange interactions (KEI) between degenerate
dγ orbitals of neighboring magnetic ions are derived not to violate the crystal symmetry with making no assumption on the transfer integrals. The KEI constants which are affected by the Hund coupling under the AFO order due to the joint effect of the cooperative Jahn–Teller effect (CJTE) and the orbital exchange interaction can explain successfully the appearance of the
A-AFS ordering. The close relation between the AFO and
A-AFS orders, the role of the CJTE, and the effect of the presence of the unfilled
dε orbitals are clarified. The obtained results are consistent with the properties of the
A-AFS order observed in LaMnO
3, MnF
3 and KCuF
3.
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Ram Kripal, Sanjay Misra
2004 Volume 73 Issue 5 Pages
1334-1340
Published: May 15, 2004
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The results of ESR studies of Cu
2+ ion doped in Ammonium Tartrate single crystal at room temperature are reported. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the spin-Hamiltonian parameters. Cu
2+(I):
gx=2.0469±0.002,
gy=2.1522±0.002,
gz=2.4489±0.002 and
Ax=(56±2)10
−4 cm
−1,
Ay=(66±2)10
−4 cm
−1,
Az=(79±2)10
−4 cm
−1. Cu
2+(II):
gx=2.0292±0.002,
gy=2.1477±0.002,
gz=2.4186±0.002 and
Ax=(36±2)10
−4 cm
−1,
Ay=(63±2)10
−4 cm
−1,
Az=(73±2)10
−4 cm
−1. The ground state wave function of the Cu
2+ ion in ammonium tartrate is evaluated. It is found that the ground state is predominantly |
x2−
y2〉.
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Yukikuni Akishige, Ryuichi Komatsu
2004 Volume 73 Issue 5 Pages
1341-1346
Published: May 15, 2004
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Real and imaginary parts, ε′ and ε″, of the dielectric constant of Li
2B
4O
7 were measured at temperatures of 10–300 K and at frequencies of 30 Hz–1.8 GHz, using two kinds of the single crystals prepared for a surface acoustic wave (SAW) device and for a nonlinear optical (OPT) device. Commonly to the both crystals, two new features were found: Debye-type dielectric dispersion appears near 2 GHz at room temperature, and a broad dielectric maximum occurs at approximately 120 K. On the other hand, only on the OPT crystal, ε′ along the
c-axis shows a small cusp at 220 K, and both ε′ and ε″ show sharp peaks at 237 K. These anomalies occur mainly on increasing temperature, and the magnitudes strongly depend on samples. In addition, the ε″ along the
c-axis increases rapidly with increasing temperature above about 230 K due to ionic conduction of mobile Li-ions as reported previously, but it shows an obvious thermal hysteresis in the temperature range of 230–300 K. We discuss causes of these peculiar dielectric behaviors above 220 K, by assuming an interaction between an incommensurate modulation wave and Li-ions, which are mobile at room temperature and freeze at low temperatures below about 230 K.
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Munetaka Taguchi, Peter Krüger, Jean-Claude Parlebas, Akio Kotani
2004 Volume 73 Issue 5 Pages
1347-1354
Published: May 15, 2004
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Extending a previous study [Phys. Rev. B
68 (2003) 035407], we present calculations for the core-level X-ray photoemission (XPS), X-ray absorption (XAS) and resonant X-ray emission spectra (RXES) at Mn
L2,3 edge in Mn thin films on Ag(001) and related structures, namely an adsorbed Mn monolayer (ML) on Ag(001) [i.e. Mn/Ag(001)], a “buried” one [i.e. Ag/Mn/Ag(001)], an adsorbed bilayer Mn/Mn/Ag(001), a free standing Mn ML, bulk body-centered-tetragonal (bct) Mn, a Mn impurity in Ag, and a single Mn atom on Ag(001). Very good agreement with experiment is obtained in 2
p XPS. Using the same parameter values, we could also reproduce the experimental 2
p XAS spectra of the Mn/Ag(001) system. The calculated RXES spectra present satellite structures which are very sensitive to the hybridization strength. We have also studied the dependence of the different spectra on the effective Coulomb parameter
Udd. The XAS and RXES spectra show a strong dependence on
Udd, which allows to estimate its value.
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Hidekazu Okamura, Masato Matsubara, Takeshi Tayagaki, Koichiro Tanaka, ...
2004 Volume 73 Issue 5 Pages
1355-1361
Published: May 15, 2004
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Infrared (IR) absorption spectroscopy has been used to probe the evolution of microscopic vibrational states upon the temperature- and photo-induced spin crossovers in [Fe(2-picolylamine)
3]Cl
2EtOH (Fe–pic). To overcome the small sizes and the strong IR absorption of the single crystal samples used, an IR synchrotron radiation source and an IR microscope have been used. The obtained IR spectra of Fe–pic show large changes between high-spin and low-spin states, for both the temperature- and the photo-induced spin crossovers. In contrast, the spectra in the temperature- and photo-induced high-spin states are relatively similar to each other, however they show distinct differences below 750 cm
−1. This demonstrates that the photo-induced high-spin state involves microscopically different characters from those of the temperature-induced high-spin state. The results are discussed in terms of local pressure and structural deformations within the picolylamine ligands, and in terms of their possible relevance to the development of macroscopic photo-induced phase in Fe–pic.
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H. Mori, T. Soma, K. Okuda, K. Wada
2004 Volume 73 Issue 5 Pages
1362-1370
Published: May 15, 2004
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The nonlinear evolution equation for the fluctuation of a terrace edge with anisotropy in step stiffness during step flow growth is derived in the two-sided model where adatoms can be incorporated into the step from the upper terrace as well as from the lower terrace. It is shown by reductive perturbation method based on the linear stability analysis that (1) up to ε
3 order in the smallness parameter of instability the nonlinear evolution equation reduces to the closed Kuramoto–Sivashinsky (KS) equation with extra coefficients compared with the one-sided model and (2) the nonlinear evolution equation up to ε
5 order is also derived in order to take into account the anisotropy in step stiffness in the lowest order. The nonlinear evolution equation is numerically calculated for various parameters included. It is also shown that the asymmetry of attachment into a step and the Gibbs–Thomson effect with anisotropy in step stiffness bring about various growth patterns of the step from chaotic growth to periodic growth and further to an inclined straight step mode with a single peak.
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Hiroshi Morita, Toshihiro Kawakatsu, Masao Doi, Daisuke Yamaguchi, Mik ...
2004 Volume 73 Issue 5 Pages
1371-1374
Published: May 15, 2004
Released on J-STAGE: July 25, 2007
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Controllable helical domain structures and some related exotic domain structures can be realized in simple diblock copolymer systems under an external field. These domain structures are obtained in self consistent field (SCF) simulations and experiments. A phase diagram constructed by SCF simulations predicts a series of morphological transitions between different domain structures by controlling the strength of the external field.
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Toshiaki Tanigaki, Yuki Kimura, Hitoshi Suzuki, Mami Kurumada, Chihiro ...
2004 Volume 73 Issue 5 Pages
1375-1376
Published: May 15, 2004
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Mitsuru Itoh, Takaaki Azuma, Tôru KyôMen, Katsunori Iio, K ...
2004 Volume 73 Issue 5 Pages
1377-1378
Published: May 15, 2004
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