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Makoto Homma, Chigak Itoi
2004 Volume 73 Issue 3 Pages
499-502
Published: March 15, 2004
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We construct a set of exact ground states with a localized ferromagnetic domain wall and an extended spiral structure in a deformed flat-band Hubbard model. In the case of quarter filling, we show the uniqueness of the ground state with a fixed magnetization. We discuss a more realistic situation given by a band-bending perturbation, which can stabilize these curious structures. We study a conduction electron scattered by the domain wall and the spiral spins.
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Hidetsugu Sakaguchi, Mitsuaki Tamura
2004 Volume 73 Issue 3 Pages
503-506
Published: March 15, 2004
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Soliton motion in some external potentials is studied using the nonlinear Schrödinger equation. Solitons are scattered by a potential wall. Solitons propagate almost freely or are trapped in a periodic potential. The critical kinetic energy for reflection and trapping is evaluated approximately with a variational method.
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Hiroshi Frusawa
2004 Volume 73 Issue 3 Pages
507-510
Published: March 15, 2004
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Recent Monte Carlo simulations [A. G. Moreira and R. R. Netz: Eur. Phys. J. E
8 (2002) 33] in the strong Coulomb coupling regime suggest strange counterion electrostatics unlike the Poisson–Boltzmann picture: when counterion–counterion repulsive interactions are much larger than counterion–macroion attraction, the coarse-grained counterion distribution around a macroion is determined only by the latter, and the former is irrelevant. Here, we offer an explanation for the apparently paradoxical electrostatics by mathematically manipulating the strong coupling limit.
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Akira Onuki
2004 Volume 73 Issue 3 Pages
511-514
Published: March 15, 2004
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We present a general theory of electric field effects in liquid crystals where the dielectric tensor depends on the orientation order. As applications, we examine (i) the director fluctuations in nematic states in an electric field and (ii) the deformation of the nematic order around a charged particle. Some predictions are made for these effects.
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Hiroshi Kontani
2004 Volume 73 Issue 3 Pages
515-518
Published: March 15, 2004
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We present a theoretical study of the Kadowaki–Woods relation in the orbitally degenerate periodic Anderson model. Based on the Fermi liquid theory, we derive
the generalized Kadowaki–Woods relationin the strong coupling limit,
Aγ
−2≈10
−5⁄\\frac12
N(
N−1) [μΩ cm (mol·K/mJ)
2], where
A is the coefficient of the
T2 term in the resistivity, γ is the
T-linear specific heat coefficient, and
N is the
f-orbital degeneracy. This result naturally explains the remarkably smaller value of
Aγ
−2 in various orbitally degenerate (mainly Yb-based) heavy Fermion systems, reported by Tsujii
et al. [J. Phys.: Condens. Matter
15 (2003) 1993].
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Dai Aoki, Etsuji Yamamoto, Yoshiya Homma, Yoshinobu Shiokawa, Akio Nak ...
2004 Volume 73 Issue 3 Pages
519-522
Published: March 15, 2004
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We succeeded in observing the de Haas–van Alphen (dHvA) oscillations in NpNiGa
5 single crystals, which were grown by the Ga-flux method. This is the first dHvA observation in transuranium compounds. The cyclotron effective masses were moderately enhanced, ranging from 1.8 to 4.9
m0 (
m0: rest mass of an electron). From an intensive change of the dHvA amplitude at 80–90 kOe and the temperature dependence of the electrical resistivity, NpNiGa
5 is most likely an antiferromagnet with a Néel temperature,
TN=30 K.
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Wataru Kobayashi, Ichiro Terasaki, Masashi Mikami, Ryoji Funahashi
2004 Volume 73 Issue 3 Pages
523-525
Published: March 15, 2004
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We have found that the thermoelectric power of the ordered perovskite CaMn
3−xCu
xMn
4O
12 is negative at high temperature (−35 μV/K at 1000 K), although this material is a hole-doped conductor in which Cu
2+ is substituted for Mn
3+. This is quantitatively explained by the extended Heikes formula, where entropy flows in a direction opposite to the charge.
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M. Kamada, S. Okuma
2004 Volume 73 Issue 3 Pages
526-529
Published: March 15, 2004
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We report on current–voltage (
I–
V) characteristics for a thick amorphous Mo
xSi
1−x film both in conventional strip-like and Corbino-disk (CD) contact geometries. In CD, vortices rotate around the sample center and we can control the gradient as well as the strength of the Lorentz force acting on the vortices. In the vortex-liquid phase, we find no significant difference in the shape of
I–
V curves between the two geometries, while in the vortex-glass phase anomaly in the
I–
V curves is visible in CD as a dip in
dlog
V⁄
dlog
I at a characteristic current
I*. Using recent simulation work by Miguel and Zapperi, we suggest that a change in the vortex dynamics from plastic flow to laminar (liquid-like) flow occurs at approximately
I*.
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Gaku Amano, Satoshi Akutagawa, Takahiro Muranaka, Yuji Zenitani, Jun A ...
2004 Volume 73 Issue 3 Pages
530-532
Published: March 15, 2004
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In this study, we investigated superconductivity at 18 K in an yttrium sesquicarbide system, Y
2C
3, by a magnetization measurement, although this material with a maximum
Tc of 11.5 K has already been investigated by Krupka
et al. in J. Less-Common Met.
17 (1969) 91. The crystal structure of Y
2C
3 is a body-centered cubic (Pu
2C
3-type) structure, and the lattice parameters are varied by heat treatment conditions. The magnetization (
M–
H) curves of this compound show a typical type-II superconducting behavior, and the lower critical field,
Hc1(0), is 3.5 mT. The
Tc value in this system is changed in the range from 15 K to 18 K, depending on sintering conditions. The sintering conditions in this work are different from those in a previous work by Krupka
et al. We successfully synthesized a new high-
Tc phase in Y
2C
3.
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Ryotaro Arita, Kazuhiko Kuroki, Hideo Aoki
2004 Volume 73 Issue 3 Pages
533-536
Published: March 15, 2004
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We propose theoretically that the application of magnetic fields can induce spin-triplet superconductivity in repulsively interacting electron systems having strong ferromagnetic spin fluctuations. We have confirmed the general idea in the Hubbard model on the triangular lattice, whose Fermi surface consists of disconnected pockets for low electron concentrations, by numerically calculating the pairing susceptibility in a moderate magnetic field with the dynamical cluster approximation combined with the quantum Monte-Carlo method.
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Kazunori Umeo, Kyoutarou Yamane, Yuji Muro, Kenichi Katoh, Yuzuru Niid ...
2004 Volume 73 Issue 3 Pages
537-540
Published: March 15, 2004
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Low-temperature properties of a heavy fermion compound YbAgGe have been investigated by electrical resistivity, specific heat and magnetization measurements on a single crystalline sample. This compound, crystallizing in the hexagonal ZrNiAl-type structure, undergoes two magnetic phase transitions at
TM1=0.8 K (second order) and
TM2=0.65 K (first order). Below
TM2, the jump of the resistivity along the
a axis indicates gap formation on the Fermi surface along the
a axis. The extremely small magnetic entropy of 0.6 J/mol K released at
TM1 is attributed to the combination of the Kondo effect and magnetic frustration effect. When the magnetic field
B||
a is increased to 5 T,
TM1 is depressed to 0 K. At this critical magnetic field, the magnetic susceptibility χ follows the Curie–Weiss law, χ
−1−χ
0−1∝
T, in a wide temperature range from 0.45 K to 300 K.
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Ryousuke Shiina, Yuji Aoki
2004 Volume 73 Issue 3 Pages
541-544
Published: March 15, 2004
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We propose a theory of the field-induced ordered state in PrOs
4Sb
12. It is based on an antiferro-quadrupolar (AFQ) interaction in the low-lying singlet–triplet subspace. Using a pseudo-spin description, we clarify a hidden symmetry in the local Hamiltonian and its relation with possible order parameters. Stable AFQ phases are determined for the direction of magnetic fields, and the effect of
Th symmetry on the anisotropic phase diagram is discussed.
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Makoto Yokoyama, Hiroshi Amitsuka, Seiichiroh Itoh, Ikuto Kawasaki, Ke ...
2004 Volume 73 Issue 3 Pages
545-548
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We have performed elastic and inelastic neutron scattering experiments on solid solutions of U(Ru
1−xRh
x)
2Si
2 with Ru-rich concentrations:
x=0, 0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with increasing
x, and correspondingly, the onset temperature
Tm (∼17.5 K at
x=0) of weak antiferromagnetic (AF) Bragg reflection decreases. For
x=0.04 and 0.05, no magnetic order is detected in the investigated temperature range down to 1.4 K. In the intermediate range, 0.02≤
x≤0.03, we found that the AF Bragg reflection is strongly enhanced. At
x=0.02, this enhancement takes place at ∼7.7 K (≡
TM), which is significantly lower than
Tm (∼ 13.7 K).
TM increases with increasing
x, and seems to merge with
Tm at
x=0.03. If the AF state is assumed to be homogeneous, the staggered moment μ
o estimated at 1.4 K increases from 0.02(2) μ
B/U (
x=0) to 0.24(1) μ
B/U (
x=0.02). The behavior is similar to that observed under hydrostatic pressure (μ
o increases to ∼0.25 μ
B/U at 1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an increase in the AF volume fraction. We also found that the magnetic excitation observed at
Q=(1,0,0) below
Tm disappears as
T is lowered below
TM.
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Hiromitsu Hori, Shoji Yamamoto
2004 Volume 73 Issue 3 Pages
549-552
Published: March 15, 2004
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In terms of spinless fermions via the Jordan–Wigner transformation along a snakelike path and spin waves modified so as to restore the sublattice symmetry, we investigate the static and dynamic properties of two-leg antiferromagnetic Heisenberg ladders. The specific heat is finely reproduced by the spinless fermions, whereas the magnetic susceptibility is well described by the modified spin waves. The nuclear spin–lattice relaxation rate is discussed in detail with particular emphasis on its novel field dependence.
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Norio Ogita, Kazushige Yamamoto, Chihiro Hayashi, Tomoyoshi Matsushima ...
2004 Volume 73 Issue 3 Pages
553-555
Published: March 15, 2004
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The hydrogen binding state in the mechanically milled graphite has been investigated by Raman scattering and infrared absorption. There is no C–H vibration signal in Raman scattering spectra, while, a C–H vibration signal has been clearly observed by infrared absorption. The dominant hydrogen configuration is C–H
2 and the contribution of C–H
3 slightly increases for a longer milling time. This result indicates the first experimental determination of the hydrogen state in the mechanically milled graphite under hydrogen gas atmosphere.
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Satoru Saito, Akira Shudo, Jun-ichi Yamamoto, Katsuhiko Yoshida
2004 Volume 73 Issue 3 Pages
557-565
Published: March 15, 2004
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For a differentiable map (
x1,
x2,…,
xn)→(
X1,
X2,…,
Xn) that has an inverse, we show that there exists a Nambu-Hamiltonian flow in which one of the initial value, say
xn, of the map plays the role of time variable while the others remain fixed. We present various examples which exhibit the map–flow correspondence.
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Hang-yu Ruan
2004 Volume 73 Issue 3 Pages
566-572
Published: March 15, 2004
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Some exact solutions of the (2+1)-dimensional modified Nizhnik–Novikov–Vesselov equation are obtained with the help of variable separation approach and bilinear method. These exact solutions describe the interactions of different types of soliton. They are the interaction between two dromions, between a line soliton and a
y-periodic soliton and between two plateau type solitons. Detail behaviors of these interactions are illustrated both in analytically and in graphically.
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Hidetoshi Konno, Peter S. Lomdahl
2004 Volume 73 Issue 3 Pages
573-579
Published: March 15, 2004
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Stochastic processes with fractional order nonlinearity that give rise to the hyper Gamma distribution are demonstrated. Nonlinear mathematical structures necessary for the appearance of the hyper Gamma distribution are also exhibited for one, two, three-dimensional systems. Information geometrical relations for their associated nonlinear Langevin equations are displayed, and their physical significance is discussed in conjunction with the fluctuation–dissipation theorem for the Langevin equations.
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Tami Machida, Kiyoshi Kawamura
2004 Volume 73 Issue 3 Pages
580-587
Published: March 15, 2004
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Electron which interact with thermal phonons is transfered between two molecules irreversibly with the probability almost unity when hopping parameter between molecules is controlled appropriately. To study this electronic process, a kinetic equation for the density matrix is derived from the quantum Liouville equation with a time-dependent Hamiltonian. An important point is that a meaningful kinetic equaion is derived when adiabatic states are employed as basis of the density matrix. The newly derived kinetic equation is applied to study the electron transfer between two molecules in the presence of the time-dependent hopping parameter.
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Takahiro Yamaguchi, Hirokazu Ohtagaki
2004 Volume 73 Issue 3 Pages
588-598
Published: March 15, 2004
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Oscillation modes of forced nonlinear systems of van der Pol type: \\ddot
x−μ(1−
x2)\\dot
x+
x=
fsin(ω
t), (\\dot
x=(
d⁄
dt)
x) are studied, where μ denotes a parameter of nonlinear damping characteristics, and
f is an amplitude of external periodic force with the angular frequency ω. Introducing a multiplicity
M of the oscillation mode π
r,s(
m,
m+1) associated with
r times
m peaks and
s times (
m+1) peaks;
M=
rm+
s(
m+1), which represents a degree of periodicity of the oscillation mode, the relations of
M to the angular frequency ω are obtained for varying ω, where the amplitude
f is fixed as the value 1. By numerical experiments, it is shown that what state of the oscillation mode π
r,s(
m,
m+1) appears for variation in ω. At first, we shall show that a set of the rotation number of the oscillation mode π
r,s(
m,
m+1) belongs a subset of Farey series. Secondly, we shall show that the region of angular frequency to the characteristics of oscillation modes consists of three disjoint regions of different types; Type1, Type2 and Type3. Furthermore, we shall show that in the region of Type1, the multiplicity
M is proportional to inverse of the angular frequency ω, and in the region of Type2, only an oscillation mode π(1) does exist. Finally, we shall show that in the region of Type3, for the case of small damping, the value of multiplicity
M decreases hyperbolically for increasing inverse of the angular frequency ω, and for the case of large damping, the value of multiplicity
M increases hyperbolically for increasing inverse of the angular frequency ω. The results obtained enables us to see what oscillation mode appears for varying the angular frequency.
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Tosizumi Aoki
2004 Volume 73 Issue 3 Pages
599-607
Published: March 15, 2004
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In the context of modified spin–wave theory, we perform a finite-temperature spin–wave calculation in the large-α region of the J
1–J
2 model, where α=
J2⁄
J1. The spin correlation functions for large separations are calculated and the correlation lengths at very low temperatures are given. The two-types of spin correlation functions with a spatial anisotropy are obtained, and each of them is expressed in terms of the two different correlation lengths. At α→∞, the J
1–J
2 model on the square lattice with a lattice spacing
a should physically be divided into the two disconnected square-lattice antiferromagnets with a lattice spacing \\sqrt2
a. At this limit, one of our two correlation functions vanishes and the other is correctly reduced to the one in the square-lattice antiferromagnet. Also the two correlation lengths are unified and are reduced to the one in the above square-lattice antiferromagnet.
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Jirohta Kasagi, Hideyuki Yuki, Taiji Baba, Takashi Noda, Junji Taguchi ...
2004 Volume 73 Issue 3 Pages
608-612
Published: March 15, 2004
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Thick target yields of α particles emitted in the
6,7Li(d,α)
4,5He reactions in PdLi
x and AuLi
x were measured as a function of the bombarding energy between 30 and 75 keV. It was found that the reaction rate in Pd at lower energies is enhanced strongly over the one predicted by the cross section for the reaction with bare nuclei, but no enhancement is observed in Au. A screening energy is introduced to reproduce the excitation function of the thick target yield for each metal. The deduced value for Pd amounts to 1500±310 eV, whereas it is only 60±150 eV for Au. The enhancement in the Pd case cannot be explained by electron screening alone but suggests the existence of an additional and important mechanism of screening in metal.
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Yukio Suezaki
2004 Volume 73 Issue 3 Pages
613-616
Published: March 15, 2004
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The nominal shear stress versus shear rate curve of the shear banding flow in non-Newtonian complex fluids was investigated for the planer rotating disc and plate geometry of the rheometer. By postulating two discrete values of the viscosity that depends on the local stress, an analytically tractable calculation could be performed and two stress-shear rate curves were obtained depending on the type of the shear banding. By use of this geometry we can specify the initial location (the rim of the disc) of the beginning of the non-Newtonian shear flow without ambiguity. In this way we can eliminate the effect of unexpected fluctuations of shear flow that could occur in homogeneous or almost homogeneous shear rate geometries. The nominal shear stress versus shear rate curve possesses the maximum and minimum values in the case of vorticity banding for shear thinning flow, while the curve becomes a monotonous increasing function for shear thickening flow. In the case of gradient banding, a wedge shaped cross section of the banding pattern was expected only for shear thinning flow and the shear rate stress curve becomes a monotonous increasing function.
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Hiroshi Amemiya, Toshiya Tanabe, Takeshi Katayama
2004 Volume 73 Issue 3 Pages
617-626
Published: March 15, 2004
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This paper is concerned with plasmas where the ion temperature is larger than the electron temperature and the cooling of ions by Coulomb interaction is important. Contrary to previous treatments on Coulomb collisions where the Coulomb logarithm is assumed to be constant, it is treated here as variable to take the effect of low energy electrons more accurately into account. This correction is found to be important especially when the ion velocity is comparable to the electron thermal velocity at which the ion cooling is most efficient. Functions from which the cooling rate is derived are obtained and compared with the previous results and then the energy relaxation of ions is calculated by integrating the cooling rate over the ion velocity distribution. The cooling time is obtained as a function of ion temperature. Some applications of the result are suggested.
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Kengo Nishio, Junichiro Koga, Toshio Yamaguchi, Fumiko Yonezawa
2004 Volume 73 Issue 3 Pages
627-633
Published: March 15, 2004
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When a material is confined in a nanometer-scale pore, novel properties not seen in a macroscopic-scale material are expected. With this situation in mind, we carry out molecular dynamics (MD) simulation for the purpose of investigating the atomic configurations of Lennard–Jones (LJ) Ar solid in a pore of 3.4 nm in diameter. These results concerning the radial distribution function, Voronoi face parameters and bond-orientational order parameter show that the atomic structure of the confined Ar solid is non-crystalline (or in other words, amorphous) with a large number of Ar atoms having the local-icosahedral symmetry. The same kinds of the atomic configurations appears in bulk LJ glasses constructed via glass transition. However, there DOES exist a remarkable difference between these two cases. The amorphous structure in a bulk Ar glass easily crystallizes, after the annealing of 0.045–0.3 ns, into a closest-packed crystal (hcp, fcc or even a random stacking). On the other hand, the amorphous structure in a nanometer-scale pore remains unchanged on annealing even after 40 ns or longer. Our results of MD simulations strongly suggests that the amorphous structure in a confined Ar solid is ‘
practically stable’ in the sense that no crystallization is observed during the time span of annealing.
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Takanao Asahi, Katsuhiko Hasebe
2004 Volume 73 Issue 3 Pages
634-638
Published: March 15, 2004
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Crystal structure of the high-pressure phase in (CH
3)
2NH
2H
2PO
4 was analyzed using X-ray diffraction data measured at
p≅1.2 GPa and
T=295(1) K. Lattice constants
a=9.057 Å,
b=9.468 Å,
c=6.822 Å, α=93.25°, space group
P2
1⁄
b11,
Z=4. Though half of PO
4 groups rotate by 50° through pressure-induced phase transition, hydrogen bonded chain structure of PO
4 along the
b- and
c-axes is preserved.
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Ryoji Kiyanagi, Kenji Tsuda, Naofumi Aso, Hiroyuki Kimura, Yukio Noda, ...
2004 Volume 73 Issue 3 Pages
639-642
Published: March 15, 2004
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The structure of Sr
3Ru
2O
7 was reinvestigated by a neutron diffraction and a convergent-beam electron diffraction (CBED) experiment on single crystals. The CBED experiment revealed that the space group of Sr
3Ru
2O
7 is Bbcb with an orthorhombic lattice with nanometer-size twin components in the crystal. Taking these observations into account, a structure analysis was carried out with the neutron data. It was found that RuO
6-octahedrons connected each other have rotated about
c-axis in the opposite direction. This result is consistent with the previous report by a powder neutron diffraction experiment.
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Takashi Ichinomiya
2004 Volume 73 Issue 3 Pages
643-648
Published: March 15, 2004
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We study the temperature and the interaction dependence of Green’s function in the attractive Hubbard model using self-consistent T-matrix approximation (SCTMA). It is found that at low temperatures, the spectrum of electrons on the Fermi surface shows a three-peak structure. On the other hand, at high temperatures, the spectrum has only two peaks. We also find that by increasing the electron–electron attraction, the temperature at which the explained three-peak spectrum appears is decreased. These results are partially explained by the static superconducting fluctuation; however, at strong coupling we need to include the effect of dynamical fluctuation. The “preformed pair” scenario of the pseudogap in high-
Tc superconductors and the validity of SCTMA for the BCS–Bose Einstein condensation crossover problem are discussed.
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Taiki Ueda, Hiroaki Shishido, Shin Hashimoto, Tomoyuki Okubo, Mineko Y ...
2004 Volume 73 Issue 3 Pages
649-655
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We have measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat and de Haas–van Alphen (dHvA) oscillation of Ce
2RhIn
8, together with the dHvA oscillation of La
2RhIn
8. In La
2RhIn
8 we detected three kinds of dHvA branches showing cylindrical Fermi surfaces, which are well explained by the result of FLAPW energy band calculations. The corresponding two dHvA branches were detected in Ce
2RhIn
8, indicating that the topology of the Fermi surface in Ce
2RhIn
8 is approximately the same as that of La
2RhIn
8. The magnetic susceptibility and magnetization of Ce
2RhIn
8 were analyzed on the basis of the crystalline electric field scheme of localized-4
f energy levels. Pressure-induced superconductivity was confirmed above 1.2 GPa from the resistivity and ac-susceptibility measurements.
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Masanori Maruyama, Koichi Kusakabe
2004 Volume 73 Issue 3 Pages
656-663
Published: March 15, 2004
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We propose that to modify zigzag edges of nanographite structures by hydrogenation, fluorination or oxidation is a method to create magnetic materials made only from light elements. These reactions and methylene addition are compared with each other in several aspects by considering a graphene ribbon having mono-hydrogenated zigzag edges as a starting material. A local-spin-density approximation was applied to the electronic band-structure calculation of nanographite ribbon structures and stability of each ribbon was tested by the first-principles manner. Among possible reactions for graphene ribbon, hydrogenation produces the largest magnetic moment per a carbon atom. Since the hydrogenation is exothermic, however, fluorination has advantage, where the reaction is endothermic. The possible maximum moment is 1/3 of that for the ideal hydrogenationed graphene ribbon. A graphene ribbon with an oxidized zigzag edge and a monohydrogenated zigzag edge possesses a partially spin-polarized flat band similar to the fluorinated ribbon. A magnetic moment appears at the monohydrogenated zigzag edge but not at the oxidized edge. No evidence of spin polarization, however, has been found for a methylene-substituted graphene ribbon.
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Hiroaki Shishido, Noriko Nakamura, Taiki Ueda, Rihito Asai, Andrei Gal ...
2004 Volume 73 Issue 3 Pages
664-668
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We have succeeded in growing a single crystal of CeNiIn
4 with the orthorhombic crystal structure by the In-flux method. CeNiIn
4 is found to order antiferromagnetically below 1.4 K, with a successive change of the magnetic structure below 0.75 K. The magnetic phase diagram was formed by the specific heat and magnetization measurements. The electronic specific heat coefficient is determined as 80 mJ/K
2·mol. From these experimental results it is concluded that CeNiIn
4 is a usual 4
f-localized compound.
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Kentaro Indoh, Aya Tobo, Hiroki Yamauchi, Kenji Ohoyama, Hideya Onoder ...
2004 Volume 73 Issue 3 Pages
669-675
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Specific heat and magnetization measurements were performed precisely on the antiferroquadruplar (AFQ) ordering compound DyB
2C
2 in order to reexamine its magnetic
B–
T phase diagrams. We find new phase boundaries in both diagrams with
B||[1 0 0] and
B||[1 1 0], and revise the field dependency of some boundaries. In the resultant diagrams, all the phase have closed regions in the
B–
T space. Two phase boundaries start from
TN in both diagrams with
B||[1 0 0] and
B||[1 1 0]. The one decreases its transition temperature with increasing field which is the same behavior just to normal antiferromagnets. The other gradually increases its transition temperature with increasing fields, which seems to satisfy behavior demanded for magnets with spontaneous magnetizations. The new-found boundary divides the previously reported AFQ phase into two phases. The one has magnetically ordered moments on the AFQ ordered quadrupoles and exists only in magnetic fields. The other is a pure AFQ phase with paramagnetic moments on the ordered quadrupoles.
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Keiichi Koyama, Kouichi Fukushima, Yoshikazu Makihara, Hironobu Fujii, ...
2004 Volume 73 Issue 3 Pages
676-680
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We have studied the magnetic and structural properties of Ce(Fe
0.9Co
0.1)
2 with the C15 cubic Laves-phase structure by low-temperature x-ray diffraction measurements in magnetic fields up to 5 T, and in the temperature range from 9 to 300 K. The C15 structure is distorted to rhombohedral symmetry at 90 K in zero magnetic field, accompanied with the magnetic phase transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) states with decreasing temperature. In the AFM state, it is observed clearly that the rhombohedral distortion state recovers the C15 structure by applying magnetic field, accompanied with the metamagnetic transition from the AFM to the forced FM states with a hysteresis in the magnetization process.
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Qingfeng Lu, Peijie Sun, Dexuan Huo, Toshio Mizushima, Yosikazu Isikaw ...
2004 Volume 73 Issue 3 Pages
681-686
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The Ni sites of an intermediate-valence compound CeNi
2Al
3 can be partially substituted with Cu atoms up to 40%. Both the unit-cell volume and the number of conduction electrons increase with the substitution. The magnetic susceptibility χ(
T), specific heat
C(
T), electrical resistivity ρ(
T) and thermoelectric power
S(
T) were measured for the Ce(Ni
1−xCu
x)
2Al
3 system. With increasing
x, the χ(
T) curve changes from that of a Pauli paramagnet to a Curie–Weiss type showing Ce
3+ local moments above
T=50 K. Huge thermoelectric power is observed in all the samples of our study. The great peak over 50 μV/K in
S(
T) curve and the broad hump in ρ(
T) curve shift down to lower temperatures, meanwhile, a ten-fold enhancement of both the electronic specific-heat coefficient γ and the linear coefficient α of
S(
T) takes place simultaneously, with increasing
x. These results reveal that the hybridization between 4f and conduction electrons is weakened by introducing the Cu atoms into the Ni sites. The effects arising from the electronic change in conduction band as well as the unit-cell volume expansion are discussed, of which the former is found to dominate the evolution of the properties in Ce(Ni
1−xCu
x)
2Al
3.
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Yasuhiro Saito, Akihisa Koga, Norio Kawakami
2004 Volume 73 Issue 3 Pages
687-693
Published: March 15, 2004
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The dynamics of a doped hole in the orthogonal-dimer spin system is investigated systematically in one, two and three dimensions. By combining the bond-operator method with the self-consistent Born approximation, we argue that a dispersive quasi-particle state in the dimer phase is well defined even for quasi-two-dimensional systems. On the other hand, a doped hole in the plaquette-singlet phase hardly itinerates, forming an almost localized mode. We further clarify that although the quasi-particle weight in the dimer phase is decreased in the presence of the interchain coupling, it is not suppressed but even enhanced upon the introduction of the interlayer coupling.
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Yu Kawasaki, Yutaka Kishimoto, Noritaka Imai, Takashi Ohno, Hidenori K ...
2004 Volume 73 Issue 3 Pages
694-697
Published: March 15, 2004
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We report the results of
209Bi-NQR measurements on the heavy-fermion compound CeRhBi with the large electronic specific heat coefficient γ∼500 mJ/mol·K
2 at 2 K. From the Bi-NQR spectra, it is proved that no magnetic ordering occurs down to 0.15 K. The temperature dependence of nuclear spin–lattice relaxation rate 1⁄
T1 clearly demonstrates a crossover from a localized regime at high temperature to an itinerant ground state with the Kondo temperature
TK of about 8 K. It is, therefore, revealed that CeRhBi is a typical heavy-fermion compound with a non-magnetic ground state, closely located at a quantum critical point. In the context of CeRhPn (Pn = Bi, Sb, As) series, where all compounds crystallize in the same orthorhombic ε-TiNiSi-type structure, no trace of gap formation is observed in 1⁄
T1 down to 0.2 K in CeRhBi, although the values of 1⁄
T1 in the Kondo semiconductors CeRhSb and CeRhAs markedly decrease at low temperatures due to the presence of excitation gap.
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Katsuhiko Tsuchida, Chihiro Kato, Toshiaki Fujita, Yoshiaki Kobayashi, ...
2004 Volume 73 Issue 3 Pages
698-702
Published: March 15, 2004
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Specific heats measurements and Ru-NMR studies have been carried out for Bi
3Ru
3O
11 and La
4Ru
6O
19, which commonly have three-dimensional linkages of edge-sharing pairs of RuO
6 octahedra. The Knight shifts, the nuclear spin–lattice relaxation rates 1⁄
T1 and the electronic specific heats
Cel of these systems exhibit anomalous temperature (
T) dependence at low temperatures, as was pointed out by Khalifah
et al. [Nature
411 (2001) 660.] for the latter system based on their experimental data of the resistivity, magnetic susceptibility and electronic specific heat. Ratios of 1⁄
T1T to the square of the spin component of the isotropic Knight shift,
Kspin estimated for these systems at low temperatures suggest that they have antiferromagnetic (AF) spin fluctuations. It is confirmed by the fact that the
T-dependences of 1⁄
T1T and
Cel⁄
T of the present systems can be explained by the self-consistent renormalization theory for three dimensional itinerant electron systems with AF spin fluctuations. All these results suggest that the AF fluctuations are the primary origin of the characteristics of their low temperature physical behavior.
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Takao Sekiya, Takatoshi Yagisawa, Nozomi Kamiya, Deependra Das Mulmi, ...
2004 Volume 73 Issue 3 Pages
703-710
Published: March 15, 2004
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Optical absorption and electron paramagnetic resonance (EPR) spectra were measured for synthetic anatase TiO
2 single crystals annealed under oxygen or hydrogen atmosphere at the desired temperatures. The as-grown crystal changed its color from pale blue through yellow to colorless by annealing under oxygen pressure. On the other hand, the contact of the colorless crystal with hydrogen gas resulted in the change of its color to pale blue or dark blue depending on annealing temperature. On repetitive heat-treatment under oxygen atmosphere, the dark blue crystal became dark green, yellow and colorless. Since the change of the crystal colors reflects difference in the defect states, repetitive control of the defect states was established in this work. The EPR spectra revealed absence of paramagnetic species in colorless crystal and presence of the conduction electrons in pale blue, dark blue and dark green crystals. The EPR spectra of pale blue crystal were asymmetric because of the existence of conduction electrons and its line shape was analyzed on the basis of normal skin effect. The yellow crystal shows complex EPR spectra. Models for various defects in these crystals are proposed.
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Masahiko Matsubara, Yoshihisa Harada, Shik Shin, Takayuki Uozumi, Akio ...
2004 Volume 73 Issue 3 Pages
711-718
Published: March 15, 2004
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Theoretical calculations of the Sc 2
p→3
d→2
p resonant X-ray emission spectroscopy (RXES) in ScF
3, ScCl
3 and ScBr
3 are performed with a ScX
6 (X = F, Cl and Br) cluster model. Effects of intra-atomic multiplet coupling and interatomic hybridization are taken into account. The cluster model parameters for these materials are determined by analyzing experimental results of X-ray photoemission spectroscopy (XPS) and RXES. Some of the results are compared with new experimental data for ScCl
3 and ScBr
3. In the RXES results, we pay attention to the intensity ratio of the spectra arising from nonbonding states, which have mainly two peaks due to the crystal field splitting. From the change of the spectral intensity in RXES we find that the character of the highest energy structure of the main peaks in X-ray absorption spectroscopy (XAS) varies from almost pure
eg state to the
eg and
t2g mixed state depending on the strength of the multiplet effect and hybridization effect.
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Mitsushi Terakami, Hideyuki Nakagawa
2004 Volume 73 Issue 3 Pages
719-726
Published: March 15, 2004
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Polarized infrared (IR) absorption measurements on CN
− or OH
− centers in cadmium halide and PbI
2 crystals were carried out at 6 K with a high spectral resolution of 0.025 cm
−1 at 2000 cm
−1 by using a FTIR spectrometer. Several sharp absorption lines with widths less than 0.1 cm
−1 are observed in the energy region of the stretching vibration, i.e. 2000 to 2250 cm
−1 for CN
− and 2500 to 4500 cm
−1 for OH
−. These lines are classified into several groups attributed to (1) an isolated center simply substituted for a halogen ion, (2) an interstitial center located between the cadmium and halogen ion sheets and (3) a coupled center with an anion vacancy or a host metal ion. Almost all of the dipole axes (bond axes) of the CN
− ions doped in MI
2 (M = Cd or Pb) are parallel to the crystal
c-axes, while those of the isolated and coupled CN
− centers in CdX
2 (X = Cl or Br) lean away from the direction of the
c-axis. The most OH
− ions doped in CdX
2 (X = Cl, Br or I) and PbI
2 are arranged in the halogen-ion planes with their dipole axes parallel to the crystal
c-axes. The first overtone yields values of χ
e and ω
eχ
e for CN
− and OH
− in CdX
2 and PbI
2. These values explain well the isotope shift of the main stretching band in CdX
2 and PbI
2.
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R. L. Chern, C. Chung Chang, Chien C. Chang, R. R. Hwang
2004 Volume 73 Issue 3 Pages
727-737
Published: March 15, 2004
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The study presents a finite difference formulation for efficiently computing band structures of three-dimensional photonic crystals. First of all, we will show how to correctly discretize the double-curl equation for the magnetic field so that the transversality condition is exactly satisfied in the discrete sense. The first few branches of nontrivial eigenfrequencies that determine the major full band gaps of photonic crystals are computed by interlacing an inverse method with conjugate gradient projection and full multigrid acceleration. The presently developed method is applied to compute band structures of photonic crystals with modified simple cubic lattice, tetragonal square spiral structure (direct and inverse structures), and diamond structure with
sp3-like configuration. The computed results for the modified simple cubic and square spiral structures are in close agreement with those obtained by previous authors. Moreover, the
sp3-like configuration made of silicon and air is reported to have a large band gap which is larger than the largest reported elsewhere in the literature.
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Jeong Won Kang, Ho Jung Hwang
2004 Volume 73 Issue 3 Pages
738-744
Published: March 15, 2004
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We have systemically investigated structural phases of potassium in carbon nanotubes using a structural optimization process applied to an atomistic simulation method. As the radius of the carbon nanotubes is increased, the structures are found in various phases from an atomic strand to multi-shell packs composed of coaxial cylindrical shells and in helical, layered, and crystalline structures. Binding energy variations of encapsulated nanowires as a function of radius were identical with those of freestanding nanowires as a function of radius. Freestanding potassium nanowires of the same structures corresponding to the potassium nanowires encapsulated in carbon nanotubes were unstable and broken at the low temperature. However, when the potassium nanowires were encapsulated in carbon nanotubes, the stability of the K nanowires increased because the walls of carbon nanotubes guarded the encapsulated K nanowire. Numbers of helical atom rows composed of coaxial tubes and orthogonal vectors of a circular rolling of a triangular network can explain multi-shell phases of potassium in carbon nanotubes.
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N. B. Arboleda Jr., H. Kasai, K. Nobuhara, W. A. Diño, H. Nakan ...
2004 Volume 73 Issue 3 Pages
745-748
Published: March 15, 2004
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We performed quantum dynamics calculations using previously obtained potential energy surfaces (PESs) for the dissociative adsorption of hydrogen molecule incident on a Mg(0001), Ti(0001), and La(0001) surface. Based on the sticking probability plots we obtained as functions of the incidence H
2 beam energy, La is the best material for hydrogen storage, followed by Ti, and then by Mg. This is due to the absence of an activation barrier in the H
2/La(0001) system. Both H
2/Ti(0001) and H
2/Mg(0001) systems have activation barriers, but the H
2/Ti(0001) system has a very small activation barrier far from the curved region of the reaction path, while the H
2/Mg(0001) system has a high activation barrier close to the curved region along the reaction path. Our results also indicate that the sticking probability has some dependence on the vibrational state of the impending H
2 molecule for the Mg, Ti and La surfaces. The degree of dependence still varies in each metal. Vibrational effect is most observed with Mg, followed by Ti, and then by La.
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Toshiaki Omori, Tsuyoshi Horiguchi
2004 Volume 73 Issue 3 Pages
749-755
Published: March 15, 2004
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We propose a dynamical neural network model with excitatory neurons and inhibitory neurons for memory function in hippocampus and investigate the effect of inhibitory neurons on memory recall. The results by numerical simulations show that the introduction of inhibitory neurons improves the stability of the memory recall in the proposed model by suppressing the bursting of neurons.
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Hideto Takekida, Kenichi Nanbu
2004 Volume 73 Issue 3 Pages
756-757
Published: March 15, 2004
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Hidetoshi Konno, Peter S. Lomdahl
2004 Volume 73 Issue 3 Pages
758-759
Published: March 15, 2004
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M. Kano, S. Masuda, A. Ogata, K. Okabe, H. Okamoto
2004 Volume 73 Issue 3 Pages
760-761
Published: March 15, 2004
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Takao Yoshinaga
2004 Volume 73 Issue 3 Pages
762-763
Published: March 15, 2004
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Yositake Takane
2004 Volume 73 Issue 3 Pages
764-765
Published: March 15, 2004
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Andrei Galatanu, Yoshinori Haga, Etsuji Yamamoto, Tatsuma D. Matsuda, ...
2004 Volume 73 Issue 3 Pages
766-767
Published: March 15, 2004
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