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Kenji Hiraga, Tetsu Ohsuna, Kazumasa Sugiyama
専門分野: Structure of liquids and solids; crystallography.
1998 年 67 巻 5 号 p.
1501-1504
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
A dodecahedral atom cluster, which is the largest atom cluster with icosahedral symmetry found in crystalline alloy phases, was observed in the cubic crystalline phase of β -(AlPdMnSi), referred to as a 2/1 approximant of an icosahedral quasicrystal, with a lattice constant of 2.0211, nm. The large dodecahedral cluster has a diameter of about 2.6, nm and contains about 480 atoms. The atomic arrangement of the dodecahedral cluster is divided into atomic shells with icosahedral symmetry, and most of the atoms in the shells are located at special positions associated with the golden mean in the three-dimensional Penrose lattice. A small icosahedral atom cluster, formed with twelve Al atoms at the vertices and a Pd atom at the center, is located at each vertex of a dodecahedral shell with a diameter of about 2, nm. The large dodecahedral atom cluster is considered to be an important cluster for understanding the structure of an Al--Pd--Mn icosahedral quasicrystal.
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Kazuhiro Fuchizaki, Kyozi Kawasaki
専門分野: Structure of liquids and solids; crystallography.
1998 年 67 巻 5 号 p.
1505-1508
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The dynamical density functional equation put forth recently in an attempt to go beyond the current mode coupling theories of supercooled liquid and glass transitions is solved by mapping to the kinetic lattice gas model.Analyses of the dynamic structure factor in the initial stage of freezingreveal that the equation correctly captures the mode coupling mechanism ofdensity fluctuations.
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Yhuji Tsujimi, Takuya Matsui, Haruo Furuta, Toshirou Yagi
専門分野: Thermal properties of condensed matter.
1998 年 67 巻 5 号 p.
1509-1512
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
An ultraslow relaxational mode with a relaxation time τ = 5 -- 8 μsec is discovered for the first time near the phase transition temperature T
c= 48.5°C in uniaxialferroelectric triglycine sulfate (NH_2CH_2COOH)_3·H_2SO_4 using time-resolved spectroscopy.The physical origin of the mode is assigned to be thermal relaxation, because dominant anisotropic anomalous behavior can be observed in the Bragg-diffracted mode intensity at time origin I(0)and can be well explained by the anisotropic anomaly of the thermal expansion coefficient α and the anomaly ofthe specific heat at constant stress C_X.The thermal diffusivity D
th evaluated from τ also shows theanisotropic anomalous behavior.This behavior is successfully interpreted by the anisotropic polarizationfluctuation characteristic of the structural phase transitions of uniaxial ferroelectrics.
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Hiroshi Tochihara, Wataru Shimada, Hiroshi Yamamoto, Masahiro Taniguch ...
専門分野: Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties).
1998 年 67 巻 5 号 p.
1513-1516
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The DAS 7× 7 surface structure is known to be the most stable on Si(111), and we investigated its formation mechanism by scanning tunneling microscopy. Triangular narrow unreconstructed-regions (“1× 1”), prepared on terraces by quenching, are chosen for in situ observation of the formation of the unit cell of the DAS 7× 7 at about 250°C. It is demonstrated that the single stacking-faulted half of the unit cell is formed or annihilated dynamically in a structural sequence of “1× 1”↔ 5× 5↔ 7× 7↔ 9× 9. The faulted half is stabilized when another neighboring faulted-half of the same size is formed during its lifetime. We propose a formation model for the 7× 7 unit cell.
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Wilson Agerico Diño, Hideaki Kasai, Ayao Okiji
専門分野: Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties).
1998 年 67 巻 5 号 p.
1517-1520
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We report that the alignment factors of hydrogen moleculesdesorbing in the vibrational ground state from Cu(111) and Pd(111)vary nonmonotonically with the final rotational state j depending onthe translational energy. Upon averaging over the Boltzmanndistribution of total kinetic energies at surface temperaturesrelevant to existing experiments, the resulting alignment factorvalue corresponds to a small preference for helicopter-like rotation.
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Makoto Kuwabara, Yukihiro Shimoi, Shuji Abe
専門分野: Electron states in condensed matter.
1998 年 67 巻 5 号 p.
1521-1524
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Competition between polaron and bipolaron inconjugated polymers with nondegenerate ground state issystematically studied in the extended Hubbard-Peierls modelwith the symmetry-breaking Brazovskii-Kirova term, using the density matrix renormalizationgroup method combined with lattice optimization in the adiabaticapproximation.We demonstrate that the relative stability of a bipolaron over twoseparated polarons sensitively depends onboth on-site Hubbard U and nearest-neighbor repulsion V.When U is much larger than V, the bipolaron state is morestabilized compared with mean field calculations.
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Yoshiteru Shimizu, Hideto Horii, Yositake Takane, Yoshimasa Isawa
専門分野: Electronic transport in condensed matter.
1998 年 67 巻 5 号 p.
1525-1528
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Josephson current through a multilevel quantum dot with strong Coulombrepulsion is studied by means of a Hartree-Fock approximation. We pay attentionto the offdiagonal Cooper pair tunneling process in which an up-spin electronand a down-spin electron are transferred to the opposite bank through differentsingle-particle levels in the dot. It is shown that, ifthe offdiagonal tunneling process isrelevant, the system can behave as a π junction even when thedot is nonmagnetic without a localized spin. It is alsofound that π-junction behavior is enhanced with increasing the number ofthe dot levels. On the other hand, if the offdiagonal tunneling process iscompletely negligible, the multilevel structure suppresses π-junctionbehavior. These results indicate that we should take the multileveleffects into account in analyzing the Josephson current through a correlatedquantum dot.
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Shuji Kawasaki, Mikio Takano, Ryoji Kanno, Takashi Takeda, Atsushi Fuj ...
専門分野: Electronic transport in condensed matter.
1998 年 67 巻 5 号 p.
1529-1532
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The electronic properties of CaFe
1-xCo
xO
3, a perovskite system dominated by oxygen-hole character, were studied experimentally. A partial Co-substitution has been found to induce a serial transformation from a charge-disproportionated, antiferromagnetic (AF), insulating phase (Phase I, x<0.1) to a charge-melted, AF, metallic phase (Phase II, 0.1≤ x<0.2) and then to a ferromagnetic and metallic phase (Phase III, 0.2
* at x=0 to |k|=0.13a* at x=0.1. We ascribe the serial transformation to broadening of the oxygen-hole band with increasing Co content.
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Kazuhiko Kuroki, Hideo Aoki
専門分野: Superconductivity.
1998 年 67 巻 5 号 p.
1533-1536
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Quantum Monte Carlo method is used to explore a link between the pairing symmetry and the shape of the Fermi surface in the two-dimensional Hubbard model. In the case corresponding to the hole-doped cuprates, where the Fermi level lies close to the van Hove singularities around (0, π), the d
x2-y2 pairing correlation is selectively enhanced, while in the electron-doped case, where the singularities are well below the Fermi level and the Fermi surface runs through (± π/2, ± π/2), both d
x2-y2 and d
xy correlations are enhanced with the latterhaving a √{2}× √{2} structure. The two pairing symmetries can mix to result in a nodeless gap.
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Weijie Zhang, Jun–ichi Igarashi, Peter Fulde
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1537-1539
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We calculate the impurity susceptibility for a spin-1/2 magnetic impurity symmetrically coupled to its two nearest-neighbor spins in an antiferromagnetic Heisenberg spin-1/2 chain. This is done by extending White's density-matrix renormalization group (DMRG) technique to finite temperatures. It is found that the impurity susceptibility satisfies Curie law at low temperatures, and thatthe Curie constant decreases rapidly with increasing coupling constant between the impurity spin and the spins in the chain. For strong couplings, a logarithmic dependence of the susceptibility on temperature emerges.The Curie law behavior agrees with the DMRG analysis at zero temperature but deviates from the prediction of conformal field theory.
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Kazuo Hida
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1540-1543
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The ground state of the square lattice bilayer quantum antiferromagnet with nearest (J_1) and next-nearest (J_2) neighbour intralayer interaction is studied by means of the dimer expansion method up to the 6-th order in the interlayer exchange coupling J_3. The phase boundary between the spin-gapphase and the magnetically ordered phase is determined from the poles of thebiased Padé approximants for the susceptibility and the inverse energy gapassuming the universality class of the 3-dimensional classical Heisenbergmodel. For weak frustration, the critical interlayer coupling decreaseslinearly with α (= J_2/J_1). The spin-gap phase persists down toJ_3=0 (single layer limit) for 0.45 <~ α <~ 0.65. Thecrossover of the short range order within the disordered phase is alsodiscussed.
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Masafumi Sera, Masahiko Hiroi, Ken–ichi Yamamoto, Norio Kobayash ...
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1544-1547
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The thermal expansion, specific heat and magnetization of CuGe
1-xSi
xO
3 have been studied. Although the Néel temperature T
N of the D+AF phase, where the antiferromagnetic (AF) phase coexists with the dimerized (D) one, is proportional to x up to 0.02 in H=0 as in Cu
1-xZn
xGeO
3, T
N of the M+AF phase, where the AF phase coexists with the magnetic (M) one above 10, T, suddenly increases with x between x=0.005 and 0.008. The AF properties in the D+AF phase are quite unusual in contrast with the normal ones in the AF state for x=0.02. This is because the AF properties in the D+AF phase are largely influenced by the existence of dimerization as a background, which exists below T
SP, and the quantum effect plays an important role in this phenomenon.
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Wakako Shiramura, Ken–ichi Takatsu, Budhy Kurniawan, Hidekazu Ta ...
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1548-1551
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The magnetic susceptibility and high-field magnetization process of NH
4CuCl
3 with double chains of CuCl
3 have been measured using single crystals. No anomaly indicative of the three-dimensional ordering is observed in susceptibility data above 1.7 K. It is found, by magnetization measurement down to 0.5 K, that in contrast to KCuCl
3 and TlCuCl
3, NH
4CuCl
3 has a gapless magnetic ground state at zero field. It is observed that the magnetization curve has two plateaus at one-quarter and three-quarters of the saturation magnetization, irrespective of the external field direction. The origin of the plateaus is attributed not to the magnetic anisotropy, but to the quantum effect. The relation between the plateaus and the period of the spin state is discussed in terms of a recent theory presented by Oshikawa et al. [Phys. Rev. Lett. 78 (1997) 1984].
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Kenji Nakajima, Yasuo Endoh
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1552-1555
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Inelastic neutron scattering experiments were carried out to study the oxygen doping effect on spin-waves in La
2NiO
4.11. The present study revealed well-defined spin-waves appearing in the low energy regions as well as in the smaller q
2D region near the antiferromagnetic zone center which are considered to be bound magnons associated with impurities. The `host' spin-waves still persist in higher energies with a short lifetime. The `impurity' mode may result from the doped hole distribution at both Ni and O sites in NiO
2 layers.
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Hiroshi Tsukada, Takao Goto, Kazuyoshi Ogasawara, Sachio Horiuchi, Hid ...
専門分野: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 年 67 巻 5 号 p.
1556-1559
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Spin lattice relaxation time of
1H in a charge-transfer complex of bisethylenedioxytetrathia fulvalene (BO) and decyltetracyanoquinodimethane (C
10TCNQ) has been measured in a low-temperature region of 2--50, K. The relaxation rate at the resonance frequency of 9.5, MHz exhibits Korringa-like behavior down to about 30, K. At lower temperatures, it exhibits a substantial increase with a peak at around 5, K and then rapidly decreases with decreasing temperature. Similar behavior is observed in the relaxation rate at a higher frequency (15, MHz), but the increase is supressed by a higher external field. These behaviors are well explained by the theory of localization in weakly disordered systems. These results indicate that at low temperatures, Anderson localization is detected in BO conductive layers.
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Atsushi Goto, Tadashi Shimizu, Haruyoshi Aoki, Masahiko Isobe, Yutaka ...
専門分野: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 年 67 巻 5 号 p.
1560-1563
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The metallic state below the charge density wave (CDW) transition temperature of Rb
3Cu
8S
6 has been studied by NMR and spin echo double resonance (SEDOR). This compound is known to show metallic characteristics below T
c2=55 K, although the CDW already sets in at T
c1=120 K. It has been found that some of the Cu-NMR lines start to spread out below T
c1, and remain broadened even below T
c2. In order to gain further insight into the state below T
c2, we applied SEDOR to the broadened Cu-lines below T
c2. A double-horned shape characteristic of CDW states was found in one of the SEDOR spectra, which is considered to be a manifestation of the presence of the CDW even below T
c2. The SEDOR reduction is attributed to a kind of motion in the CDW chains. On the other hand, the spin-lattice relaxation rate at the Rb sites was found to decrease rapidly below T
c2, implying that the Rb sites are not inert, but play important roles in this metallic state. As a possible mechanism for this anomalous metallic state, the spinless (charged)-soliton conduction on the CDW chains is discussed.
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Yasumasa Kajinaga, Takayuki Tsuchida, Miki Wadati
専門分野: Mathematical methods in physics.
1998 年 67 巻 5 号 p.
1565-1568
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
By using the perturbation method of multiple scales, we derive coupled nonlinear Schrödinger equations as amplitude equationsfrom coupled nonlinear Klein-Gordon equations. Such coupled nonlinear Schrödinger equations are not necessarilyintegrable. We present the reductions to the known integrable coupled nonlinearSchrödinger equations.
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Toru Ebisawa, Dai Yamazaki, Seiji Tasaki, Takeshi Kawai, Masahiro Hino ...
専門分野: Classical and quantum physics: mechanics and fields.
1998 年 67 巻 5 号 p.
1569-1573
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Easy quantum beat experiments have been developed using a new cold neutron spin interferometer, which brings us easy observation of quantum beat phenomena. The quantum beat is created by the coherent superposition of the spin eigenstates of cold neutron with different energy states, which are produced with two radio-frequency flippers. We observed quantum beat phenomena with a range of frequency from 4 kHz to 10
-5 Hz, which correspond to the energy differences from 1.66 × 10
-11 eV to 4.1 × 10
-20 eV. The principle and the arrangement of the quantum beat experiment are discussed, and typical measurement data are presented. Some applications of the quantum beat experiments are briefly proposed.
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Norihiro Tsushima, Tsuyoshi Horiguchi
専門分野: Statistical physics and thermodynamics.
1998 年 67 巻 5 号 p.
1574-1582
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We obtain phase diagrams of a spin-3/2 Ising model on a square lattice by using a corner transfer matrix renormalization group method. We find that three phases appear in the phase diagrams; they are the ferromagnetic(FM) phase, the paramagnetic(PM) phase and a ferrimagnetic(FI) phase. It turns out that a tricritical point appears in a region of space spanned by parameters of coupling constants and the temperature. We estimate values of critical exponent ν and α at a transition temperature between the FM phase and the PM phase, at that between the FI phase and the FM phase, and also at that between the FI phase and the PM phase, by using the finite size scaling analysis.
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Kyungsik Kim, J. S. Choi, Y. S. Kong
専門分野: Statistical physics and thermodynamics.
1998 年 67 巻 5 号 p.
1583-1586
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The multifractal behavior of the normalized first passage time is investigated on the two dimensional Sierpinski gasket with both absorbing and reflecting barriers. The normalized first passage time for Sinai model and the logistic model to arrive at the absorbing barrier after starting from an arbitrary site, especially obtained by the calculation via the Monte Carlo simulation, is discussed numerically. The generalized dimension and the spectrum are also estimated from the distribution of the normalized first passage time, and compared with the result on a finitely square lattice.
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Yoshihiro Yamazaki
専門分野: Statistical physics and thermodynamics.
1998 年 67 巻 5 号 p.
1587-1593
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Interface equations of motionfor a single tetragonal nucleus growth and for twin formationunder elastic fields in cubic-tetragonalstructural transitions are derived.We give an expression to the elastic energyin the form of non-local, long-range interactionsbetween nonconserved order parameters.We find that a single tetragonal nucleus grows anisotropicallyinto oval or square and that twin structure is a stationary statein the coarsening process.These results are consistent with the numerical simulation.
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Takashi Taneichi, Takayoshi Kobayashi
専門分野: Atomic spectra and interactions of atoms with photons.
1998 年 67 巻 5 号 p.
1594-1596
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
A theory for the position-dependent dynamics of an atom confined in a cavity with a movable-boundary mirror is developed. The mirror motion induces substantial transition between two optically uncoupled atomic states.
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Hiroaki Fukuta, Youichi Murakami
専門分野: Fluid dynamics.
1998 年 67 巻 5 号 p.
1597-1602
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Linear stability of the Kolomogrov flow U(y), which shows the long-wave instability in unbounded region, is investigated in restricted region { -∞ < x < ∞, 0 ≤ y ≤ L π } under two kinds of boundary conditions:a real viscous boundary condition and a virtual stress-free boundary condition.It is shown numerically and analytically that a finite-wave instability appears instead of the long-wave instability owing to the confinement.The numerical results suggest that the critical Reynolds number R_c(L) and the critical wavenumber α_c (L) tend to those in unbounded region as R_c(L) -R_c(∞) ∝ L
-1, α_c(L)-α_c(∞)(=0) ∝ L
-0.5.This power law is different from that for the finite-wavenumber instability. The effect of the difference of the boundary condition on the stability is also elucidated. It is shown numerically that it does not affectthe critical values except for small systems (L<5).
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Osamu Moriyama, Naoya Kuroiwa, Masaaki Kanda, Mitsugu Matsushita
専門分野: Fluid dynamics.
1998 年 67 巻 5 号 p.
1603-1615
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Time series signals of several flowing patterns of granular particles (rough sand) through a vertical pipe have been analyzed by the wavelet expansion method. Probability distribution functions (PDFs) of wavelet coefficients, which roughly correspond to the density increments over a given scale, are constructed. It is revealed that PDFs for the sparse and uniform flow were Gaussian distribution over wide scales. On the other hand, those of uniform but dense flow were exponential distributions and the time series signals had strong correlations between adjacent length scales. PDFs of density waves were a little more complex: When the resistance force due to the medium air was weak, they were Gaussian. When it became strong, however, PDFs of density waves changed their shape according to the scales one observes. On large scales, they were Gaussian. As the length scale became smaller, PDFs were gradually deformed from Gaussian to exponential. It implies the existence of intermittent density waves, which reminds us of fully developed turbulence.
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Osamu Moriyama, Takeshi Isoda, Naoya Kuroiwa, Masaaki Kanda, Ismael R& ...
専門分野: Kinetic and transport theory of fluids; physical properties of gases.
1998 年 67 巻 5 号 p.
1616-1624
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Density waves of granular particles (rough sand) in a vertical pipe are experimentally investigated under the condition where the medium (air) flow is well controlled. When a cock attached to the bottom-end of the pipe is open, air is dragged by falling granular particles and flows together with sand. No density waves are observed for this situation. As the cock is gradually closed, however, the pressure gradient of air inside the pipe becomes larger and, as a result, density waves of granular particles emerge. Power spectrum P(f) of time series signals of density waves shows a clear power-law form P(f) -- f
-α and the precise measurements indicate that the exponent α is close to 4/3. The value of α is robust even under the medium flow as far as density waves can be seen.
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Kazunobu Nagasaki, Tohru Mizuuchi, Sakae Besshou, Hisamichi Funaba, Ka ...
専門分野: The physics of plasmas and electric discharges.
1998 年 67 巻 5 号 p.
1625-1635
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Dependence of plasma profiles on the power absorption of electron cyclotron heating is experimentally studied in the Heliotron-E helical device. A focused Gaussian beam with controllable polarization makes it possible to change the power absorption. The electron density and temperature profiles are sensitive to the single pass absorption rate. The electron temperature profile is peaked and the density profile is hollow as the single pass absorption increases. The resonance position is also important for determining their profiles. The electron temperature profile is changed from a peaked one to a hollow one, depending on the resonance position. The non-diffusive outward flow, which is necessary to form a hollow temperature profile, is estimated by using a simple heat transport model.
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Lourdes Mestres, Maria Luisa Martinez–Sarrion, Manuel Morales, A ...
専門分野: Structure of liquids and solids; crystallography.
1998 年 67 巻 5 号 p.
1636-1642
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
X-ray and neutron powder diffraction studies of Rb
2-x(NH
4)
xSO
4 solid solutions throughout the concentration range 0≤ x≤ 2 and in the temperature range from 10 up to 300, K have been carried out. From the concentration dependencies of the lattice parameters obtained for protonated and deuterated samples, the tricritical point have been determined near the concentration x=1.6. The β -γ phase transition is of the first order for compounds with x>1.6 and of the second order for x<1.6.
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Tatsuhiro Yogi
専門分野: Structure of liquids and solids; crystallography.
1998 年 67 巻 5 号 p.
1643-1648
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The molecular-dynamics method was used to simulate a hydrogen fluoride fluid of 500 particles interacting through Lennard-Jones potential function of the intermolecular separation r and the electric dipole interaction between hydrogen fluorides. The present work represents the partial radial distribution functions for two variates, self-diffusion constant and surface tension of liquid HF over a wide temperature range. The evidence of existence of dimer (HF)_2 and the possibility of hydrogen bonding between HF molecules are examined.
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Yasuhisa Yamamura, Kazuya Saito, Michio Sorai, Isao Ikemoto
専門分野: Equations of state, phase equilibria, and phase transitions.
1998 年 67 巻 5 号 p.
1649-1654
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Effects of an impurity on a displacive phase transition are examined for crystalline biphenyl (BP) by adiabatic calorimetry.While the anomaly in the heat capacity remained unchanged by 1% of naphthalene (NA), the anomaly disappeared at 1% of 4, 4
′-difluorobiphenyl (DFBP).The observed effect is discussed in relation tothe localization of the soft-mode.Two impurities differ in the existence/absence of the twisting degree of freedom that produces the soft-mode.The DFBP molecule weakly localizes the lattice vibration of BP crystalover the wide range of distance.The localization by the NA molecule is strongand only the close neighboring BP molecules are affected.
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Tomoko Tsuchiya, Makoto Katori
専門分野: Equations of state, phase equilibria, and phase transitions.
1998 年 67 巻 5 号 p.
1655-1666
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The λ-state chiral Potts model on a finite directed latticeis defined, whose partition function under a certain boundarycondition becomes the directed percolation (DP)probability for a finite lattice in the λ → 1 limit.We also introduce the system of m friendly walkers of Ltime-steps and prove that its generating functionof trajectories is equal to the partition function of the λ-state chiral Potts model when m=(λ-1)/2.Combining these results gives a new formula for the DP probabilitygiven by a double limit L → ∞ and m → 0of the generating function of the m friendly walkers.We define the critical value p
c(m) for the infinitesystem of m friendly walkers.Numerical study supports our conjecture that the critical valuep
c for the DP probability is given by the m → 0extrapolation of p
c(m).
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Tomozo Tomoyose, Mitsuhiro Seino
専門分野: Transport properties of condensed matter (nonelectronic).
1998 年 67 巻 5 号 p.
1667-1671
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The number density fluctuation of mobile ions in superionic conductors (SIC) is studied by using the coupled phonon-lattice gas model. The dynamical structure factor of SIC of α-AgI type is calculated by using the generalized Langevin equation for the number density fluctuation caused by the mobile ion hopping. It is found that the calculated dynamical structure factor is of a non-Lorentzian type with asymmetric temperature dependence.
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Bruno Lindquist, Rolf Riklund
専門分野: Electron states in condensed matter.
1998 年 67 巻 5 号 p.
1672-1676
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
A one-dimensional discrete tight-binding model with nearest-neighbour interaction is studied. We use the transfer model with variable hopping matrix elements, here assuming the two values t or -t, and constant on-site potential. Under this conditions all the eigenstates are known to be extended. It is shown that if the distribution of the off-diagonal matrix elements constitutes a deterministic aperiodic sequence, the eigenstate corresponding to the middle eigenvalue is periodic for some choices of the sequence, but not for all. The studied sequences that turn out to have a periodic middle state are the Thue-Morse sequence, the Rudin-Shapiro sequence and many of the generalised Thue-Morse sequences but not for instance the well known Fibonacci sequence.
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Yoshiyuki Yoshida, Rikio Settai, Yoshichika Onuki, Humihiko Takei, Kiy ...
専門分野: Electron states in condensed matter.
1998 年 67 巻 5 号 p.
1677-1681
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We have observed the de Haas-van Alphen (dHvA) oscillation of Sr_2RuO_4, the layered perovskite superconductor not based on copper.The Fermi surface was confirmed to be a corrugated cylinder.This characteristic feature of the Fermi surface brings about a large angular dependence of the dHvA amplitude, which is explained by the spin-splitting zero in the dHvA oscillation and the Yamaji effect.
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Shuntaro Yoda, Kosaku Yamada
専門分野: Electron states in condensed matter.
1998 年 67 巻 5 号 p.
1682-1687
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We investigate the two-dimensional Hubbard modelwith the long-range Coulomb interaction.We assume the form of the effective Coulomb interaction, which is treated as a perturbation.For the half-filling case, the self-energy is numerically evaluatedup to the second-order terms of the perturbation expansionwith the full momentum dependence included.The k-mass is calculated from this self-energy.It is found that the first-order term makesa dominant contribution to the reduction of the k-mass.
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Jian–Xin Zhu, Z. D. Wang
専門分野: Electronic transport in condensed matter.
1998 年 67 巻 5 号 p.
1688-1692
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We investigate the conductance through an Aharonov-Bohm normal metal ring connected to normal and superconducting leads. It is shown that, due to the Andreev reflection at the normal superconducting phase boundary, the conductance maxima could be enhanced to be twice as large as that for the ring connected with normal conducting leads. The voltage bias may suppress this conductance enhancement. However, the periodicity of the oscillating conductance in flux is not altered by the presence of the superconducting contact. The discussion is also extended to include the impurity scattering effect and the multichannel case. Quite interestingly, the period halving could be induced by the impurity scattering even in one-dimensional normal superconducting hybrid structures.
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Minoru Sasaki, Shuuji Tanaka, Hiroshi Negishi, Masasi Inoue, Reizo Kat ...
専門分野: Electronic transport in condensed matter.
1998 年 67 巻 5 号 p.
1693-1703
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Pulsed-laser induced transient thermoelectric effect (TTE) and magnetotransport measurements have been made for molecular conductors (DMe-DCNQI)
2Cu (h salt) and its deuterated crystals (d
7 salt) along the c-axis over the temperature range 4.2--300, K. The photogenerated TTE voltage decays exponentially with two characteristic relaxation times τ
1 and τ
2 due to hole diffusions, followed by a thermal diffusion process of photogenerated phonons. From these relaxation times, we have estimated the corresponding hole mobilities μ
1 and μ
2 (especially μ
1 at low temperature exceeds as high as 6, 000, cm
2/Vs), which show an unusually strong temperature dependence at high temperatures (μ
1, μ
2∝ T
-3 for the h salt and μ
2∝ T
-3.5 for the d
7 salt), suggesting the presence of any anomalous scattering mechanism in these salts, in addition to conventional neutral impurity and phonon scatterings. Furthermore, with special ohmic contacts to a tiny sample, we have successfully measured the positive Hall voltage and magnetoresistance for the h salt, both of which show a nonlinear magnetic-field dependence. The galvanomagnetic properties of the h salt are reasonably explained by a two-carrier model mainly of two types of holes located around the Γ and P points in the Brillouin zone of the three-dimensional (3D) anisotropic band, with concentrations, p
Γ and p
P, and mobilities, μ
Γ (=μ
2) and μ
P (=μ
1), respectively. Moreover, we have calculated the temperature dependence of the dc conductivity, in general accord with the observations, whose analyses yield the Fermi energy for the d
7 salt, E
F = 42, meV (enhancement of E
F), compared to 20, meV for the h salt, and the effective mass at the P point [m
P = 1.6m
0 for the h salt and m
P = 2.3m
0 for the d
7 salt, compared to the theoretical values around the Γ point, m
Γ=(3.6--4.3)m
0]. The carrier transport along the c-axis at low temperature is mostly due to the holes around the Γ point, while, at high temperatures, electrons in the one-dimensional (1D) electron band are also responsible for the carrier transport; the temperature dependence of its conductivity follows the power law σ
e ∝ T
-1.9. Finally, we have discussed a possible band model for both salts, where the enhancement of the hole Fermi energy by partial deuteration in the DMe-DCNQI molecule is important to induce the metal-insulator transition occurring in the d
7 salt.
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Tsuneya Ando, Takeshi Nakanishi
専門分野: Electronic transport in condensed matter.
1998 年 67 巻 5 号 p.
1704-1713
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
The effective potential of an impurity in a k·p scheme is derived in two-dimensional graphite sheet.When the potential range is smaller than the lattice constant, it has an off-diagonal matrix element between K and K
′ points comparable to the diagonal element.With the increase of the range, this off-diagonal element decreases rapidly and the diagonal element for envelopes at A and B sites becomes identical.The crossover between these two regimes occurs around the range smaller than the lattice constant.In the latter regime, back scattering between states with +k and -k vanishes identically for the bands crossing the Fermi level in the absence of a magnetic field, leading to an extremely large conductivity.The absence of the back scattering disappears in magnetic fields, giving rise to a huge positive magnetoresistance.
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Jun–ichiro Kishine, Kenji Yonemitsu
専門分野: Superconductivity.
1998 年 67 巻 5 号 p.
1714-1731
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Based on the perturbative renormalization group (PRG) approach, we have studied dimensional crossovers in Hubbard ladders coupled viaweak interladder one-particle hopping, t
⊥.We found that the one-particle crossover is strongly suppressed throughgrowth of the intraladder scattering processes which lead the isolatedHubbard ladder system toward the spin gap metal (SGM) phase.Consequently when t
⊥ sets in, there exists, for any finite intraladder Hubbard repulsion, U>0, the region where the two-particle crossover dominates the one-particle crossover and consequentlythe d-wave superconducting transition, which is regarded as a bipolaroncondensation, occurs. By solving the scaling equations for the interladder one-particle andtwo-particle hopping amplitudes, we give phase diagrams of the system with respect to U, t
⊥0 (initial valueof t
⊥) and the temperature, T.We compared the above dimensional crossovers with those in a weakly coupled chain system, clarifying the differencebetween them.
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Masanori Taira, Morio Suzuki, Xu–Guang Zheng, Tsutomu Hoshino
専門分野: Superconductivity.
1998 年 67 巻 5 号 p.
1732-1737
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
Two kinds of junctions were fabricated on a single crystal and a polycrystal of Bi
2Sr
2CaCu
2O
8-x. The tunneling conductance characteristics, G(V) were measured for the former junction at temperatures from 4.2 K to 100 K, and for the latter one at temperatures from 8.7 K to 90 K. It was found that the conductance peak (CP) at zero-bias is observed for tunneling direction perpendicular to a c-axis, but is not observed for tunneling direction parallel to a c-axis. Kashiwaya et al. theoretically predicted that the junction fabricated on a d-wave superconductor can give various G(V) characteristics scattering from a s-wave like spectrum to a d-wave like one, and has CP under certain boundary condition. In the present investigation, the measured G(V) characteristics in the high T
c Bi-system superconductor were found to qualitatively agree with the theoretical prediction by Kashiwaya et al.
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Takashi Sugiyama, Masanori Ichioka
専門分野: Superconductivity.
1998 年 67 巻 5 号 p.
1738-1747
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
For the d
x2-y2 superconductors, we investigate the fourfold symmetry of the upper critical fields and magnetization related to the torqueunder the parallel magnetic field to the ab plane of the crystal.We take into account the s-wave order parameter induced from the spatial variation of the d
x2-y2-wave order parameter.In addition, we investigate the effects of the shape of the Fermi surface.If the pairing interaction for the s-wave channel is attractive, the s-wave component can enhance the above fourfold symmetry.Depending on the structure of the Fermi surface, the fourfold symmetric anisotropy in the ab plane enhances or suppressesthe fourfold symmetric behavior.There is also the case where the fourfold symmetric anisotropyof in the ab plane changes the sign of the fourfold symmetric behavior from that of the isotropic case.
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Kenji Kamishima, Mikhail I. Bartashevich, Tsuneaki Goto, Makoto Kikuch ...
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1748-1754
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We have measured the magnetization and magnetostriction of Mn
3GaC in pulsed high magnetic fields up to 37, T and the magnetization under steady magnetic field and pressure up to 0.82, GPa. Mn
3GaC is antiferromagnetic (AF) at low temperatures. It exhibits successive transitions to an intermediate (I), to a ferromagnetic (F) and to a paramagnetic phase. The transition between the AF and I phases is first order and the others are second order. The transition temperature between the I and F phases does not change greatly with increasing magnetic field. At low temperatures, a metamagnetic transition from the AF to the I state is observed. Volume magnetostriction measurement at 4.2, K indicates that the volume is abruptly decreased by the metamagnetic transition and then gradually shrinks with increasing field. High pressure stabilizes the F phase and enhances the Mn moment.
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Norikazu Tanaka, Kazuko Motizuki
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1755-1761
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
To study the anisotropy of g-factor of Cu
2+ ion in the antiferromagnetic Bi
2CuO
4 having an interesting crystal structure, we calculate the energy splitting of the orbital state of Cu
2+ ion due to the electric crystalline field arising from the surrounding O
2-, Bi
3+ and Cu
2+ ions. On the basis of Pryce's spin Hamiltonian we evaluate g-tensor of each Cu
2+ ion in the unit cell. We also study the magnetic anisotropy energy caused by the dipole-dipole interaction and anisotropic exchange interaction. The results are discussed in connection with observations.
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Tetsuji Kuramoto
専門分野: Magnetic properties and materials.
1998 年 67 巻 5 号 p.
1762-1766
発行日: 1998/05/01
公開日: 1999/10/01
ジャーナル
認証あり
We study magnetic and critical properties of the alternating spin antiferromagnetic Heisenberg chain with S=1/2 and 1 in a magnetic field at T=0. The numerical diagonalization is applied to the system up to 2N=20 sites. Checking numerically that magnetic states with the magnetization per site m obey a conformal field theory with conformal anomaly c=1 for 1/4
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