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Fumiko Ogushi, Satoshi Yukawa, Nobuyasu Ito
2006 Volume 75 Issue 7 Pages
073001
Published: July 15, 2006
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The density profiles of the gas–liquid interface of the three-dimensional Lennard-Jones (12-6) particle system are studied by nonequilibrium molecular dynamics simulation. The system is a rectangular parallelepiped box of the size of
Lx>>
Ly×
Lz. Two Nosé–Hoover heat baths with different temperature are attached to the regions near both ends in the
x-direction. Heat flows in the system in the
x-direction and it maintains the system in a gas–liquid coexisting state. A gas–liquid interface exists steadily in the system box and an asymmetric density profile is observed. We consider the characteristic lengths ξ
g and ξ
l in the gas and liquid phase sides defined using density in each phase ρ
g,l=
aξ
g,l−3, respectively. The sum of the characteristic lengths ξ=ξ
g+ξ
l corresponds to the thickness of the interface. Using ξ
g,l, the density profile in the interface is well described by the tanh form in each phase side ρ
g,l(
x)=ρ
g,l+β
g,ltanh|(
x−
x0)⁄ξ
g,l|. The critical behavior of this model is consistent with the three-dimensional Ising universality.
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Naoki Kawashima
2006 Volume 75 Issue 7 Pages
073002
Published: July 15, 2006
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An approximate numerical approach to spin models is proposed, in which the original lattice is transformed into a tree. This method is applied to the Edwards–Anderson spin glass model in two and three dimensions. It captures the characteristics of each individual sample and reproduces various qualitative features of sample averaged quantities similar to those that have been observed in previous Monte Carlo simulations. For example, from the Binder parameter for various system sizes as a function of the temperature we obtain
T∼1.0 with ν∼1.85, in reasonable agreement with previous Monte Carlo simulations. The present approximation yields the trivial structure for the overlap distribution function.
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Makoto Umeki
2006 Volume 75 Issue 7 Pages
073401
Published: July 15, 2006
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Gledzer’s cascade shell model of turbulence with six real variables is studied numerically using MATHEMATICA 5.1. The Poincaré plot of the first mode
v1 is used to determine periodic, doubly periodic and chaotic solutions and the routes to chaos via both frequency locking and period doubling. The circle map on the torus is well approximated by the summation of several sinusoidal functions. The dependence of the rotation number on the viscosity parameter is in accordance with that of the sine circle map. The complicated bifurcation structure and the revival of a stable periodic solution at a smaller viscosity parameter in the present model indicates that the turbulent state may be very sensitive to the Reynolds number.
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Takayuki Makino, Atsushi Tsukazaki, Akira Ohtomo, M. Kawasaki, Hideomi ...
2006 Volume 75 Issue 7 Pages
073701
Published: July 15, 2006
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We have grown nitrogen-doped ZnO films by two kinds of epitaxial methods on lattice-matched ScAlMgO
4 substrates. We measured the photoluminescence (PL) of the two kinds of ZnO:N layers in the donor–acceptor-pair transition region. The analysis of the excitation-intensity dependence of the PL peak shift with a fluctuation model has proven that our observed growth-technique dependence can be explained in terms of the inhomogeneity of charged impurity distribution. It was found that the inhomogeneity in the sample prepared with the process that provides showing better electrical properties was significantly smaller in spite of the similar nitrogen concentration. The activation energy of acceptors has been evaluated to be ≈170 meV, which is independent of the nitrogen concentration.
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Yoshikazu Tanaka, Masafumi Sera, Koichi Katsumata, Stephen W. Lovesey, ...
2006 Volume 75 Issue 7 Pages
073702
Published: July 15, 2006
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Observations on an ordered alloy Ce
0.7Pr
0.3B
6 by non-resonant X-ray diffraction are reported. We find incommensurate reflections (2δ,1⁄2,0) (δ∼0.23) below about 3 K in zero applied magnetic field. The wave vector dependence of the intensity is compelling evidence for the first direct observation of an incommensurate multipolar ordering (MPO). The incommensurate MPO appears to coexist with a commensurate MPO with a wave vector (1⁄2,1⁄2,1⁄2), which is the ground state configuration. Additional insight to the properties is derived from extensive measurements made with the alloy placed in a magnetic field ranging up to 6 T. We propose that a competition among RKKY-like exchange interactions between the Ce–Ce, Ce–Pr, and Pr–Pr multipoles is a main source for the appearance of the incommensurate MPO.
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Dai Aoki, Yoshinori Haga, Yoshiya Homma, Hironori Sakai, Shugo Ikeda, ...
2006 Volume 75 Issue 7 Pages
073703
Published: July 15, 2006
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We succeeded in growing single crystals of NpFe
4P
12 using the Sn-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat. This is the first single crystal growth of transuranium filled-skutterudite compounds. NpFe
4P
12 is found to order ferromagnetically below
TC=23 K. The magnetic moment is directed along the 〈100〉 direction with the saturated moment of 1.35 μ
B/Np. The large resistivity value indicates that NpFe
4P
12 might be a semimetal, where the 5
f electrons are localized with a 5
f3 configuration, indicating Np
4+. The electronic specific heat coefficient γ is found to be small, γ\\simeq10 mJ/(K
2·mol), which is consistent with the low carrier system.
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Yukikuni Akishige
2006 Volume 75 Issue 7 Pages
073704
Published: July 15, 2006
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Cubic and hexagonal BaTiO
3 single crystals doped with KF (Ba
1−xK
xTiO
3−xF
x with
x=0.1) were grown from a solution with a molar ratio of BaO+2TiO
2+10KF. The cubic BaTiO
3 crystals with
x=0.1 undergo a second order ferroelectric phase transition at the Curie temperature
TC of 35 °C; the dielectric constant ε
′ along the [100] direction shows a peak at
TC reaching 12000. Further, a spontaneous polarization appears below
TC; the remanent polarization
Pr and the coercive field
Ec are 7 μC cm
−2 and 1.3 kV/cm at 20 °C, respectively. Furthermore, a large piezoelectric constant
d33=300 pC/N was observed at 20 °C. On the other hand, in hexagonal BaTiO
3 with
x=0.1, ε
′ along the hexagonal
c-axis increases monotonously with decreasing temperature and saturates at low temperatures like quantum paraelectrics.
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Hiroshi Tanida, Hiroyuki S. Suzuki, Shigeru Takagi, Hideya Onodera, Ka ...
2006 Volume 75 Issue 7 Pages
073705
Published: July 15, 2006
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The magnetic and thermodynamic properties of PrMg
3 single crystals were investigated based on the magnetic susceptibility χ(
T) and the specific heat
CP(
T). An observed broad anomaly in
CP(
T) with a peak ∼1.8 J/(mol K) at 0.9 K, together with Van-Vleck-like behavior of χ(
T), indicates that the low-
T properties are ascribed to the multipole (quadrupole
O20 and
O22, and octupole
Txyz) degrees of freedom of a nonmagnetic, non-Kramers Γ
3 doublet ground state in the cubic crystalline electric field of Pr
3+. The low-
T CP(
T) anomaly, however, is not described in terms of the two-channel Kondo model, but is more similar to that for the single-channel Kondo model with the Kondo temperature
TK=1.3 K, including its weak external-field dependence. No evidence for a cooperative phase transition was detected down to 0.54 K in
CP(
T), suggesting that the Γ
3 multipole degrees of freedom are quenched at low
T by forming a strongly correlated electronic state through the hybridization with conduction electrons.
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Masahiko Isobe, Shigenori Koishi, Naomi Kouno, Jun-Ichi Yamaura, Touru ...
2006 Volume 75 Issue 7 Pages
073801
Published: July 15, 2006
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We have synthesized hollandite vanadate, K
2V
8O
16, by a solid-state reaction under 4 GPa at 1473 K for one hour, and investigated its structural and electromagnetic properties. We found a metal–insulator transition with a two-step jump of resistivity of about three orders at around 170 K. The magnetic susceptibility is reduced to a small value at the transition, suggesting the formation of V
4+–V
4+ singlet pairs and V
3+–V
3+ pairs in the low-temperature insulator phase. The transition is of first order accompanied by a structural change from a tetragonal to a monoclinic structure. The low-temperature phase has a superlattice of \\sqrt2
a×\\sqrt2
a×2
c, where
a and
c denote the parameters of the primitive cell for the simple tetragonal hollandite structure, suggesting a charge ordering of V
4+ and V
3+. We construct a possible charge order model from the obtained results, in which two kinds of double-chain formed by V
3+ and V
4+ chains and by single V
4+ chains order in a manner that gives a superlattice of \\sqrt2×\\sqrt2 in the
a–
b plane. The V
4+–V
4+ and V
3+–V
3+ pairs are formed in each chain along the
c-axis, resulting in a duplication of the
c-axis.
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Hiroto Kuninaka, Hisao Hayakawa
2006 Volume 75 Issue 7 Pages
074001
Published: July 15, 2006
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With the aid of the simulation of a two-dimensional mechanical model, the equilibration process of a contact of elastic materials and a quasi-static collision of elastic materials are investigated. To reproduce Hertzian contact theory and the quasi-static theory of inelastic collisions, the introduction of defect particles is important as well as the choice of proper boundary conditions.
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Yoshio Yamaguchi
2006 Volume 75 Issue 7 Pages
074101
Published: July 15, 2006
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The new version of quantum mechanics (QM) with the finite momentum space (maximum momentum value
K) is presented along the line already described in the series of papers by the present author. Our QM is a generalized version of the relativistic QM proposing generalized Lorentz transformations forming a non-abelian group, a specific and convenient form of the set of transformations among “general relativistic transformations”. Our theory offers an intermediate type of “relativity” between special relativity (SR) and general relativity (GR). One of interesting consequences is described for the neutrino flux from very high energy particle–particle (say hadron–hadron or lepton–hadron) collisions, which gives the ratio of neutrino mass
mν and the maximum momentum
K. Bound states should have the maximum momenta ν
K, with ν being a positive integer and fractional number. Also quantum field theories are briefly mentioned.
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Shingo Suzuki, Noriyuki Shimakura
2006 Volume 75 Issue 7 Pages
074301
Published: July 15, 2006
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Single electron-capture cross sections in collisions of bare and hydrogen-like ions with lithium-like ions of C, N, and O are calculated in the collision energy range between 0.05 and 16 keV/amu using a molecular-state close-coupling method. For the lithium-like ions, both the ground and first excited states are considered. The cross sections are calculated for capture into
n=2 and 3 states of the bare and hydrogen-like ions and for excitation and de-excitation of the lithium-like ions. None of the electron-capture cross sections are larger than 10
−15 cm
2 in the collision energy range considered in the present study. At lower collision energies, the cross sections decrease due to Coulomb repulsion between the ions. Partial cross sections for capture into 1s3s, 1s3p, and 1s3d levels for the hydrogen-like ion collisions are on the same order of magnitude because the final states are mixed with each other by the electric field induced by the helium-like ions.
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Takashi Kimura, Shunji Tsuchiya, Makoto Yamashita, Susumu Kurihara
2006 Volume 75 Issue 7 Pages
074601
Published: July 15, 2006
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We study the first- and second-order superfluid–Mott insulator transitions of spin-1 bosons in an optical lattice under a magnetic field by the Gutzwiller approximation. We find that, in contrast to previous perturbative studies, the phase boundary curve continuously changes as a function of magnetic field. We also find a sharp cusp structure on the phase boundary curve under some circumstances. When the phase boundary curve deviates from that obtained with the perturbative studies, the phase transition is a first-order one. We further clarify the specific features of the phase transition in the present system. The order parameters exactly at the boundary point, where the transition changes from first to second order, remain finite under a finite magnetic field and continuously vanish as the magnetic field approaches zero.
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Takanori Fukami, Ruey-Hong Chen
2006 Volume 75 Issue 7 Pages
074602
Published: July 15, 2006
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A monoclinic form of potassium dihydrogen phosphate, KH
2PO
4, crystal has been crystallized. X-ray diffraction and differential scanning calorimetry measurements have been performed on this compound. The space group symmetry (monoclinic
P2
1) and the crystal structure of this compound are determined at room temperature. It has been found that there are ten possible O–H–O hydrogen bonds with O–O distances in the range from 2.561(3) to 2.642(3) Å. Five transitions are found at temperatures around 432, 483, 512, 544, and 668 K. The transition at 432 K is suggested to be produced by a chemical reaction of thermal decomposition accompanied with a dynamic disorder of the H atoms on the hydrogen bonds.
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Toru Moriwaki, Yuichi Akahama, Haruki Kawamura, Satoshi Nakano, Kenich ...
2006 Volume 75 Issue 7 Pages
074603
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The pressure-induced structural phase transition of MgH
2 was examined up to 57 GPa at room temperature. α-MgH
2 with the rutile-type structure at ambient conditions transformed to γ-MgH
2 with the α-PbO
2 structure. A complete conversion to the γ-phase, however, did not take place and these two phases coexisted up to 9 GPa. Above 9 GPa, MgH
2 transformed to the orthorhombic phase (HP1-phase), and further to another orthorhombic phase (HP2-phase) at around 17 GPa. Space groups of the HP1-phase and the HP2-phase were concluded to be
Pbc2
1 and
Pnma (cotunnite-type), respectively. Cotunnite-type MgH
2 was stable at pressures up to 57 GPa. Thus the proposed structural sequence of MgH
2 under pressure is rutile-type → α-PbO
2 →
Pbc2
1 → cotunnite-type, with an increase in the coordination number of magnesium ions from 6 to 9.
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Kiyoshi Torizuka, Hiroyuki Tajima, Takashi Yamamoto
2006 Volume 75 Issue 7 Pages
074604
Published: July 15, 2006
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We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)
2Li
1−xCu
x (
x=1 and 0.75) over a wide temperature range between 4 and 250 K. The electronic contribution can be analyzed particularly below ∼80 K. A thermal hysteresis depending on the Cu concentration
x has been observed between the heating and cooling processes. The system stays in a metallic state when the sample is cooled from room temperature, while a small fraction of insulating islands is created in the metallic state when heated up to room temperature. The insulating islands survive even at high temperatures. This mechanism gives rise to the hysteretic behavior. Heat conduction is sensitive to the difference in the two phases, in contrast with electrical resistivity.
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Tomoya Isoshima, Sungkit Yip
2006 Volume 75 Issue 7 Pages
074605
Published: July 15, 2006
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The spinor Bose–Einstein condensate of atomic gases has been experimentally realized by a number of groups. Further, theoretical proposals of the possible vortex states have been suggested. This paper studies the effects of the quadratic Zeeman energy on the vortex states. This energy was ignored in previous theoretical studies, although it exists in experimental systems. We present phase diagrams of various vortex states by considering the quadratic Zeeman energy. The vortex states are calculated by the Gross–Pitaevskii equation. Several new types of vortex states are found. Further, it is found that the quadratic Zeeman energy affects the direction of total magnetization and results in a significant change in the phase diagrams.
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Tetsushi Ishikawa, Yasuhiro Nakazawa, Satoshi Yamashita, Masaharu Ogun ...
2006 Volume 75 Issue 7 Pages
074606
Published: July 15, 2006
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Low-temperature heat capacity measurements are performed on the organic superconductor (MDT-TSF)(AuI
2)
0.436; its critical temperature determined by the transport measurement is 4.5 K. A broad but reproducible thermal anomaly related to the superconducting transition is observed during precise measurements of the heat capacity under magnetic fields of up to 6 T. An important finding is that almost 60% of the normal electron density of states remains even in the superconducting ground state. This phenomenon and the intrinsic broadening of the thermal anomaly are common to another organic superconductor κ-(BEDT-TTF)
4Hg
2.89Br
8, in which an incommensurate relationship exists between anion and donor lattices. However, it is emphasized that (MDT-TSF)(AuI
2)
0.436 exhibits the superconducting transition at a relatively high temperature despite the small electronic heat capacity coefficient γ and non-dimerized molecular arrangement in the donor layers.
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Takehisa Hasegawa, Koji Nemoto
2006 Volume 75 Issue 7 Pages
074701
Published: July 15, 2006
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We apply the real space renormalization group (RG) to the replica Hamiltonian of the two dimensional Ising Edwards–Anderson model to discuss the existence of the spin glass (SG) phase. We derive the RG equations under the replica symmetric (RS) ansatz and the resulting flow diagram indicates the existence of the SG phase. The critical exponent for the SG transition has a plausible value while that of the multicritical point (MCP) is a complex number. We consider that this failure at the MCP is due to not taking the RS breaking into account. Indeed we find that the RS breaking parameter is relevant both at the SG critical point and the MCP, indicating the nontriviality of the SG phase of this model.
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Ko-Ichi Kajiyoshi, Takashi Kambe, Masafumi Tamura, Kokichi Oshima
2006 Volume 75 Issue 7 Pages
074702
Published: July 15, 2006
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We have studied the ground state of an organic quasi-one-dimensional (Q1D) ferromagnet, the γ-phase
para-nitrophenyl nitronyl nitroxide (γ-
p-NPNN), by low-frequency ESR and magnetic torque measurements, and have found that it is an antiferromagnetically ordered state with an orthorhombic anisotropy. Antiferromagnetic resonance (AFMR) modes are observed below 0.6 K. From the angle dependence of AFMR, the spin easy axis is found to point the [0\\bar11] direction. The spin-flop (SF) field is estimated to be 520 Oe. From the analysis of the AFMR modes in terms of a mean-field approximation, we have estimated the interchain interactions and the anisotropy field parameters in the ground state. The magnetic phase diagram along the spin easy axis has been determined using a high sensitive microcantilever technique. On the field dependence along the easy axis, the torque response shows anomalies at 520 Oe and around 2100 Oe, corresponding to the spin-flop and the full-polarization of spins, respectively. The easy axis and anisotropy in the antiferromagnetic state are found to be well explained by our calculations of the dipolar energy with respect to the spin structure obtained in this work.
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Shoji Yamamoto, Hiromitsu Hori, Yuji Furukawa, Yusuke Nishisaka, Yuzur ...
2006 Volume 75 Issue 7 Pages
074703
Published: July 15, 2006
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The nuclear spin–lattice relaxation time
T1 of
31P nuclei in the title compound is measured for the first time and interpreted in terms of a modified spin–wave theory. We establish a novel scenario for one-dimensional ferrimagnetic spin dynamics — it is
three-magnon processes enhanced by exchange scattering, rather than Raman processes, that make the major contribution to 1⁄
T1.
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Masami Haino, Aya Tobo, Eiichi Matsuoka, Kenji Ohoyama, Hideya Onodera
2006 Volume 75 Issue 7 Pages
074704
Published: July 15, 2006
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Magnetic
B–
T phase diagrams were examined by magnetization and specific heat experiments on the single crystalline Tb
1−xY
xB
2C
2 (0.2≤
x≤0.5) compounds, and neutron diffraction experiments was performed on the powder Tb
0.5Y
0.511B
2C
2 sample. The magnetization curves evidence that the field-induced transition occurs from phase IV into phase II′ through a mixed phase of both phases, where phase IV is antiferromagnetic and phase II′ is a field-induced phase with the antiferromagnetic and antiferroquadrupolar order. The mixed phase (IV+II′) is enhanced by the Y-dilution, and the lower and upper verges of the mixed phase become clearer in the differential magnetization
dM⁄
dB–
B curves. The Y-dilution results in scaling down of the ordered phases regions in the
B–
T space. The ways of scale down of the ordered phase are different between two field directions along the tetragonal [100] and [110]-axes, that is, the anisotropy of phase stability is increased by the Y dilution. It is supposed that the enhancement of anisotropic phase stability by the Y dilution may be due to the symmetry of the multipoles and the anisotropic multipolar interactions weakened by the Y dilution.
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Taketo Moyoshi, Yukio Yasui, Minoru Soda, Yoshiaki Kobayashi, Masatosh ...
2006 Volume 75 Issue 7 Pages
074705
Published: July 15, 2006
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Neutron inelastic scattering studies on aligned crystals of Na
xCoO
2·
yD
2O containing bilayer (
y∼1.3), monolayer (
y∼0.6) and non-deuterated (
y=0) phases have been carried out. Significant scattering has been observed for phonons originating from the vibrations of the short-range ordered D
2O molecules. No firm evidence for the magnetic fluctuations has been found for the Na
xCoO
2·
yD
2O, while the very weak intensity modulation observed in the scans along (1⁄2,1⁄2,
l) suggests the existence of the antiferromagnetic fluctuations in the non-deuterated parts of the sample, the volume fraction of which is estimated to be about 26%. The present results indicate that magnetic fluctuations, especially ferromagnetic ones, are rather weak in the deuterated system, which is consistent with the results of the NMR Knight shift reported by our group. We also discuss the short-range ordered state of D
2O, by analyzing the observed diffuse scattering.
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K. Yagasaki, T. Nakama, M. Hedo, Y. Uwatoko, Y. Shimoji, S. Notsu, K. ...
2006 Volume 75 Issue 7 Pages
074706
Published: July 15, 2006
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Two types of spinel compound CuIr
2S
4 samples were investigated: sample 1 was synthesized under protective Ar atmosphere to avoid contamination by oxygen, whereas sample 2 was exposed to oxygen during preparation procedure. According to the results of scanning electron microscopy, the oxygen concentration in sample 2 is 5 times higher than in sample 1. However, the metal–insulator transition (MIT) temperature is the same for both samples irrespective of oxygen concentration. The conductivity σ in the insulating phase (LIP) is proportional to exp[−(
T*⁄
T)
1⁄2] at
T≤120 K for sample 1 and at
T≤50 K for sample 2, while in the metallic phase the resistivity ρ is proportional to the same function of σ in LIP for both samples. Temperature independent diamagnetic susceptibility and temperature dependence of thermopower suggest that this compound is not a normal activation-type semiconductor. The electronic configuration of CuIr
2S
4 is estimated to a first approximation from the experimental results. 5
dε electrons do not participate in the crystallization bonds of
dγ
2s1p3 for spinel structure, however these electrons are responsible for MIT and for conductivity. The cooperative Jahn–Teller effect with dimerization is proposed for MIT: The energy of an electronic system of 5
dε decreases at the expense of crystallographic energy coming from the
dγ
2s1p3 electron system due to tetragonal deformation as in normal Jahn–Teller effect. Further triclinic deformation occurs to minimize energy by dimerization of 5
dε(
xy) orbitals in the 〈110〉 direction, resulting in charge ordered Pierls state. A new type of conductivity named traveling dimer conduction is proposed.
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Tsutomu Watanabe, Hisatoshi Yokoyama, Yukio Tanaka, Jun-ichiro Inoue
2006 Volume 75 Issue 7 Pages
074707
Published: July 15, 2006
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A half-filled-band Hubbard model on an anisotropic triangular lattice (
t in two bond directions and
t′ in the other) is studied using an optimization variational Monte Carlo method, to consider a Mott transition and superconductivity arising in κ-(BEDT-TTF)
2X. Adopting wave functions with doublon–holon binding factors, we reveal that a first-order Mott (conductor-to-nonmagnetic insulator) transition takes place at
U=
Uc, approximately of the bandwidth, for a wide
t′⁄
t range. This transition is not directly connected to magnetism. Robust
d-wave superconductivity appears in a restricted parameter range: immediately below
Uc and the moderate strength of frustration (0.4\\lesssim
t′⁄
t\\lesssim0.7), where short-range antiferromagnetic correlation sufficiently develops but does not come to a long-range order. The relevance to experiments is also discussed.
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Nguyen Van Hieu, Hiroaki Shishido, Tetsuya Takeuchi, Arumugam Thamizha ...
2006 Volume 75 Issue 7 Pages
074708
Published: July 15, 2006
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We grew single crystals of NdRhIn
5, TbRhIn
5, DyRhIn
5, and HoRhIn
5 with the tetragonal crystal structure and measured the magnetic susceptibility and magnetization. NdRhIn
5 is an antiferromagnet with a Néel temperature
TN=11.6 K. Below
TN, magnetization reveals two metamagnetic transitions at
Hm1=70 kOe and
Hm2=93 kOe for the magnetic field along the [001] direction. The saturation moment of 2.5 μ
B/Nd is in good agreement with the staggered Nd moment determined by the neutron diffraction experiment. These metamagnetic transitions correspond to the change of the magnetic structure. TbRhIn
5, DyRhIn
5 and HoRhIn
5 are found to be antiferromagnets with
TN=47.3, 28.1, and 15.8 K, respectively. The magnetization curves of these compounds are also quite similar to those of NdRhIn
5, revealing two metamagnetic transitions. The magnetic structures in magnetic fields are proposed by considering the exchange interactions based on the crystal structure.
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Kazuo Hida
2006 Volume 75 Issue 7 Pages
074709
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The multiple reentrant quantum phase transitions in the
S=1⁄2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength
J and even numbered bonds can take the values
JS and
JW (
JS>
J>
JW>0) randomly with the probabilities
p and 1−
p, respectively. The pure version (
p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0<
p<1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.
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Masaaki Matsuda, Kazuhisa Kakurai, Shuji Ebisu, Shoichi Nagata
2006 Volume 75 Issue 7 Pages
074710
Published: July 15, 2006
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Neutron diffraction measurements on a powder sample of α-Tb
2S
3 were performed. This material consists of a stacking of square lattice Tb1 and triangular lattice Tb2 planes and exhibits two magnetic phase transitions at ∼3.5 and ∼12 K. It was found that the Tb1 and Tb2 moments behave quite independently. The Tb1 moments show a collinear antiferromagnetic ordering at ∼12 K with the magnetic unit cell same as the chemical one. On the other hand, the Tb2 moments start to order at ∼3.5 K without affecting the magnetic order of the Tb1 moments. The magnetic structure is noncollinear with a magnetic unit cell double of the chemical one along the
a- and
c-axes. The ordered moments of the Tb1 and Tb2 moments are ∼8μ
B, similar to the full moment for the free Tb
3+ ion. These results indicate that the Tb1 and Tb2 moments are completely decoupled due to an orbital contribution, which probably gives rise to a noncollinear structure in the triangular lattice plane. The results are discussed in comparison with those of the related system α-Gd
2S
3, which has no orbital degree of freedom.
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Yositake Takane
2006 Volume 75 Issue 7 Pages
074711
Published: July 15, 2006
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In a superconductor coupled with a ferromagnetic metal, spin and charge imbalances can be induced by injecting spin-polarized electron current from the ferromagnetic metal. We theoretically study a nonequilibrium distribution of quasiparticles in the presence of spin and charge imbalances. We show that four distribution functions are needed to characterize such a nonequilibrium situation, and derive a set of linearized Boltzmann equations for them by extending the argument by Schmid and Schön based on the quasiclassical Green’s function method. Using the Boltzmann equations, we analyze the spin imbalance in a thin superconducting wire weakly coupled with a ferromagnetic electrode. The spin imbalance induces a shift δμ (−δμ) of the chemical potential for up-spin (down-spin) quasiparticles. We discuss how δμ is relaxed by spin–orbit impurity scattering.
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Mami Kurumada, Chihiro Kaito
2006 Volume 75 Issue 7 Pages
074712
Published: July 15, 2006
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Various molybdenum oxide particles such as MoO
3, Mo
4O
11, Mo
4O
11 (60M) were produced from vapor phase by controlling the total pressure of Ar–O
2 mixed gas or oxygen partial pressure. The correlation between infrared (IR) spectra and their structure were discussed taking into account the [MoO
6] octahedron. The particle size effect on the symmetry of the [MoO
6] octahedron of MoO
3 was also discussed on the basis of the harmonic oscillator model.
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Ken-ichi Sasaki, Shuichi Murakami, Riichiro Saito
2006 Volume 75 Issue 7 Pages
074713
Published: July 15, 2006
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By considering the continuous model for graphene, we analytically study a special gauge field for the edge state. The gauge field explains the properties of the edge state such as the existence only on the zigzag edge, the partial appearance in the
k-space, and the energy position around the Fermi energy. It is demonstrated utilizing the gauge field that the edge state is robust for surface reconstruction, and the next nearest-neighbor interaction which breaks the particle-hole symmetry stabilizes the edge state.
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Shuichi Wakimoto, Hiroyuki Kimura, Masaki Fujita, Kazuyoshi Yamada, Yu ...
2006 Volume 75 Issue 7 Pages
074714
Published: July 15, 2006
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We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La
2−x(Sr,Ba)
xCuO
4 with 0.07≤
x≤0.20 observed by the neutron diffraction technique. For all compositions, a sharp superlattice peak of the low-temperature-orthorhombic (LTO) structure is replaced by a pair of ICD peaks with the modulation vector parallel to the CuO
6 octahedral tilting direction, that is, the diagonal Cu–Cu direction of the CuO
2 plane, above the LTO–HTT transition temperature
Ts. The temperature dependences of the incommensurability δ for all samples scale approximately as
T⁄
Ts, while those of the integrated intensity of the ICD peaks scale as (
T−
Ts)
−1. These observations together with absence of ICD peaks in the non-superconducting
x=0.05 sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.
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Kazufumi Suenaga, Gendo Oomi, Yoshiya Uwatoko, Kesami Saito, Koki Taka ...
2006 Volume 75 Issue 7 Pages
074715
Published: July 15, 2006
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The electrical resistivity ρ in various magnetic fields and the structure of [Co(1.02 nm)/Cu(
tCu)]
25 magnetic multilayers (MML) have been investigated to clarify the relationship between the transport properties (electrical resistivity and magnetoresistance) and structure (orientation and strain of these layers). The in-plane compressive strain ε of antiferromagnetic (AF) Co/Cu MML with
tCu=1.05 nm is larger than that of ferromagnetic (F) Co/Cu MML with
tCu=0.76 nm. Furthermore, it is found that ε of the AF-Co/Cu MML is proportional to the magnitude of giant magnetoresistance, whereas that of F-MML is independent of magnetoresistance. This implies that the strain in AF-Co/Cu MMLs showing GMR is closely related to the spin-dependent scattering of conduction electrons at interfaces.
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Tsuneya Ando
2006 Volume 75 Issue 7 Pages
074716
Published: July 15, 2006
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The static polarization function is calculated in two-dimensional graphite and used for the calculation of the conductivity limited by charged-impurity scattering. The conductivity increases in proportion to the electron concentration and the mobility remains independent of the Fermi energy, in qualitative agreement with experiments. The screening increases in proportion to temperature at sufficiently high temperatures in contrast to the behavior in conventional two-dimensional systems, leading to the mobility increase proportional to the square of temperature.
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Yoshiaki Kobayashi, Taketo Moyoshi, Hidekazu Watanabe, Mai Yokoi, Masa ...
2006 Volume 75 Issue 7 Pages
074717
Published: July 15, 2006
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Studies of the NMR Knight shift
K of Na
0.3CoO
2·
yH
2O have been carried out in detail. The suppression of
K by the occurrence of the superconductivity reported previously by the present authors in both magnetic field directions perpendicular and parallel to the
c-axis has been confirmed, indicating that the Cooper pairs are in the singlet state. The anisotropy of the suppression amplitudes is consistent with the anisotropy of the hyperfine coupling constant
Aspin estimated from the
K–χ plot. It has also been found that even samples that do not exhibit a significant the Curie–Weiss-like increase of the uniform magnetic susceptibility χ with decreasing temperature
T, exhibit superconducting transition, which indicates that the superconducting Na
0.3CoO
2·1.3H
2O is not necessarily in the region of proximity of the ferromagnetic phase. It has also been confirmed that the superconducting transition temperature
Tc of the samples prepared by mixing Na
0.7CoO
2, H
2O (or D
2O) and bromine for 4 h, and separating the resultant powder from the solution by filtration, depends on the elapsed time
t after filtration. For these samples, the Curie–Weiss component of χ estimated at low temperatures increases with
t, supporting the idea that the number of lattice imperfections possibly due to oxygen-vacancy formation increases with
t. Even for such samples, the superconductivity appears, which seems to exclude the possibility of an anisotropic superconducting order parameter. These results are favorable for full-gapped superconductivity.
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A. D. Thakur, T. V. Chandrasekhar Rao, S. Uji, T. Terashima, M. J. Hig ...
2006 Volume 75 Issue 7 Pages
074718
Published: July 15, 2006
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We have investigated the presence of a two-peak feature spanning the peak effect (PE) region in the ac susceptibility data and magnetization hysteresis measurements over a wide field–temperature regime in few weakly pinned single crystals of 2
H-NbSe
2, which display a reentrant characteristic in the PE curve near
Tc(0). We believe that the two-peak feature evolves into a distinct second magnetization peak (SMP) anomaly well separated from the PE with gradual enhancement in the quenched random pinning.
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Akira Oosawa, Kazuhisa Kakurai, Yoichi Nishiwaki, Tetsuya Kato
2006 Volume 75 Issue 7 Pages
074719
Published: July 15, 2006
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Polarized neutron inelastic scattering experiments have been carried out in the quasi-1D Ising-like antiferromagnet TlCoCl
3. We observed the longitudinal magnetic fluctuation
Szz(
Q,ω) for the spin-wave excitation continuum, which has not yet been observed in unpolarized neutron inelastic scattering experiments on the quasi-1D Ising-like antiferromagnets CsCoCl
3 and TlCoCl
3, together with the transverse magnetic fluctuation
Sxx(
Q,ω). We compared both the obtained intensities of
Sxx(
Q,ω) and
Szz(
Q,ω) with those calculated using the perturbation theory from the pure Ising limit by Ishimura and Shiba (IS), and a semi quantitative agreement was found.
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Mikio Uruichi, Kyuya Yakushi, Hiroshi M. Yamamoto, Reizo Kato
2006 Volume 75 Issue 7 Pages
074720
Published: July 15, 2006
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We present the optical conductivity, infrared- and Raman-active charge-sensitive phonon modes, and the x-ray diffraction superlattice spots of β″-(ET)(TCNQ) [ET = bis(ethylenedithio) tetrathiafulvalene, TCNQ = 7,7,8,8-tetracyanoquino-dimethane], which is characterized as a quarter-filled narrow band system. Above ∼170 K, we found weak superlattice spots and splitting of the C=C and C–S stretching modes of ET. These results indicate the charge-ordering state in the ET layer. As the temperature is decreased, the superlattice spots abruptly disappeared at ∼170 K and the split modes continuously merged into a single band below ∼170 K. Concomitantly, the spectral weight of the optical conductivity ascribed to the ET layer significantly shifts toward lower energy. Through the analyses of these experimental results, we propose the view that the incoherent conducting electron in the ET layer shows a crossover behavior into a coherent Fermi liquid state below the structural phase transition at ∼170 K.
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Hiroshi Tanida, Shigeru Takagi, Hiroyuki S. Suzuki, Isamu Satoh, Takem ...
2006 Volume 75 Issue 7 Pages
074721
Published: July 15, 2006
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Microscopic properties have been investigated on a cubic nonmagnetic non-Kramers Γ
3 doublet ground-state (GS) system PrAg
2In by complementarily utilizing
115In (
I=9⁄2) and
109Ag (
I=1⁄2) NMR with particular emphasis on the low-frequency (low-ω) dipole and multipole (octupole and/or quadrupole) fluctuations of
f-electrons as probed by the nuclear spin relaxation rates 1⁄
115T1 and 1⁄
109T1. We show that 1⁄
115T1 and 1⁄
109T1 are anomalously enhanced respectively below ≅50 K and ≅100 K over those expected for the low-ω dipole fluctuations of the excited magnetic Γ
4 and Γ
5 states in a simple crystalline-electric-field model for a Γ
3 GS system. By comparing 1⁄(
115T1T) and 1⁄(
109T1T) and also by considering an invariant form of the hyperfine and/or quadrupole couplings of Γ
3 octupole and/or quadrupole moments with Ag/In nuclear dipole and/or quadrupole moments, we show that Γ
3 octupole fluctuations dominate 1⁄
109T1 and quadrupole ones can possibly contribute to 1⁄
115T1 at low
T.
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Takashi Yokota, Kanemitsu Ootsu, Fumihito Furukawa, Takanobu Baba
2006 Volume 75 Issue 7 Pages
074801
Published: July 15, 2006
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A large-scale interconnection network is a complex system that comprises numerous independent switching elements (routers). Its performance is proportional to the offered traffic load if the load is light. However, once the load surpasses a certain threshold and the network becomes congested, its performance is drastically degraded. Such nonlinear characteristics are empirically known. Nevertheless, congestion behavior has not been sufficiently investigated. In this paper, we present phase transition phenomena in interconnecting networks using cellular automata. We first simplify the interconnection network model and then propose a cellular automata model of the interconnection network. Simulation results reveal myriad phenomena from car traffic applications. Probabilistic small-scale congestion grows to a large spherical cluster where the mobility of message packets is quite low. The behavior of the spherical congested area is discussed analytically. We introduce entropy as a measure for representing the congestion. The formulation of the congested area decreases entropy, and phase transition is observed clearly. Furthermore, the temporal behavior of a congested area and entropy are revealed.
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Jun Ohkubo, Muneki Yasuda, Kazuyuki Tanaka
2006 Volume 75 Issue 7 Pages
074802
Published: July 15, 2006
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We analyze a preferential urn model with randomness using the replica method. The preferential urn model is a stochastic model based on the concept “the rich get richer.” In the replica analysis, we clarify that the preferential urn model with randomness shows a fat-tailed occupation distribution. We discuss the intuitive picture of the preferential urn model, a relationship between quenched and annealed systems, and a trial for the application of the preferential urn model to econophysics. The analytical treatments and results would be useful for various research fields such as complex networks, stochastic models, and econophysics.
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Aoi Inomata, Takeshi Shimomura, Seiji Heike, Masaaki Fujimori, Tomihir ...
2006 Volume 75 Issue 7 Pages
074803
Published: July 15, 2006
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We measured the electrical current-voltage characteristics of λDNA in vacuum using fine electrodes with a gap of about 200 nm. It was found that the electrical resistance of λDNA molecules between the fine electrodes had a large variation: from 7.8 MΩ to values larger than 1 TΩ. This was consistent with the controversial results given in previous reports. The temperature dependence of conductivity was explained well by the Arrhenius equation. In addition, the conductivity of a single molecule of double-stranded λDNA was measured by a “one-by-one” cutting method using atomic force microscopy (AFM). The conductivity was determined to be 3×10
1 S/cm, which is about the same order as that of semiconductors.
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Yo Sasaki, Naoki Kobayashi, Shunji Ouchi, Mitsugu Matsushita
2006 Volume 75 Issue 7 Pages
074804
Published: July 15, 2006
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A vertical profile of landform looks similar to the one-dimensional Brownian motion trace. It is regarded as a self-affine curve characterized by the Hurst scaling exponent,
H (0<
H<1). The fractal dimension
De for the pattern of entire contour lines including all islands, and
Dc for a single contour line can be both calculated from
H as
De=2−
H and
Dc=2⁄(1+
H). The size distribution of islands follows the power-law (the Korcak’s law) with the exponent, ζ, characterized by
De as ζ=
De⁄2. We confirmed these scaling laws both on computer-simulated landforms and real coastlines, although the former is dependent on the system size and the latter includes disturbing effects of coastal processes. The value of
H, which expresses a relief characteristic of the three dimensional self-affine surface such as landform, can be calculated from a horizontal section by these three scaling laws.
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Yasuo Narumi, Koichi Katsumata, Urs Staub, Koichi Kindo, Makoto Kawauc ...
2006 Volume 75 Issue 7 Pages
075001
Published: July 15, 2006
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