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Tsuruji Iwai, Masahiro Kimura
1990 Volume 59 Issue 11 Pages
3807-3810
Published: November 15, 1990
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The optogalvanic signal has been observed in a Cs/Ne hollow cathode discharge tube by means of pulsed laser irradiation. The observed time dependence exhibits evidence of the Penning ionization process in which the short-lived excited atom Ne
*(2
p2) takes part: Ne
*(2
p2)+Cs→Ne+Cs
+*(5
d)+e. Observation also suggests the importance of the Penning process through the autoionizing states of Cs.
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Koji Ohkitani
1990 Volume 59 Issue 11 Pages
3811-3814
Published: November 15, 1990
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For a class of flows with uniform velocity gradients, the vorticity equation is reduced to an eigenvalue equation where vorticity serves as an eigenvector of the rate-of-strain tensor. This class includes a solution in which the strain is constant and the vorticity grows exponentially as exp (λ
t), with the initial eigenvalue λ(>0). A case of special interest is obtained when both the strain and the vorticity have the same time-dependence, that is, they blow up as (1−λ
t)
−1 at a finite tame. The blow-up problem for passive scalar dynamics is also discussed.
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Sanae-Inoue Itoh, Kimitaka Itoh
1990 Volume 59 Issue 11 Pages
3815-3818
Published: November 15, 1990
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A new refined model of the L-mode and H-mode transition in tokamaks is presented based on the bifurcation of the radial electric field,
Er, near the edge. The radial gradient of
Er is newly introduced to explain the sudden change of fluctuations as well as plasma fluxes at the onset of transition. This nodel predicts that the L- to H-mode transition is associated with the decrease of d
Er⁄d
r causing reduction of particle and energy fluxes at the critical gradient.
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Motohiro Matsuura, Makoto Hagiwara
1990 Volume 59 Issue 11 Pages
3819-3822
Published: November 15, 1990
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Nonlinear susceptibility
X2 is investigated in a quasi-two-dimensional complex magnet, CoCl
2-GIC (graphite intercalation compound). A negative divergence and another different singularity that
X2 changes its sign from negative to positive, are concluded to occur at the upper and the lower critical points in the compound by observing nonlinear magnetic response to an AC excitation field. From the facts, it is shown that the symmetry of
X2 at the critical point reveals a breaking of spatial magnetic symmetry in the examined systems. On this basis, the dynamical structure of hierarchical spin ordering is discussed.
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Hidetsugu Kitatani, Takehiko Oguchi
1990 Volume 59 Issue 11 Pages
3823-3826
Published: November 15, 1990
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The ferromagnetic-nonferromagnetic phase boundary on the two-dimensional ±
J Ising model in the
p-
T plane is determined by the use of the coherent-anomaly method (CAM) proposed by Suzuki, where
p is the concentration of the +
J bond, and
T the temperature. The phase boundary below the Nishimori line has been found to be vertical at
p=0.884±0.001 to the
p-axis, which is consistent with the previous results obtained under the assumption of Suzuki’s weak universality. The critical exponent γ
p(
T) has also been determined along the phase boundary, which shows a crossover tendency.
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Satoru Ohta, Takejiro Kaneko, Hajime Yoshida
1990 Volume 59 Issue 11 Pages
3827-3830
Published: November 15, 1990
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The temperature (
T) dependence of lattice parameters and the pressure effect on the charge-density wave (CDW) transition temperature
Tt for V
3Te
4 with NiAs-like crystal structure are reported. The thermal expansions of lattice parameters
a(
T) and
b(
T) below
Tt deviate upwards from their linear variation above
Tt, while both
c(
T) and β(
T) hardly change in the temperature range between 20 K and room temperature. In the pressure (
P) range up to 10.9 kbar, the pressure dependence of
Tt can be described by the expression,
Tt(
P)=(195.8±2.1) exp [−(0.025±0.002)
P] K with
P in kbar.
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Takao Yamamoto, Noriko Akutsu, Yasuhiro Akutsu
1990 Volume 59 Issue 11 Pages
3831-3834
Published: November 15, 1990
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We introduce a coarse-grained terrace-step-kink model which includes multispecies steps. The multispecies step system expresses a surface of a complex crystal such as the ice crystal. The surface free energy and the equilibrium crystal shape are calculated. We find that the facet shape is given by an arithmetic mean of those for constituent species. The multispecies system also exhibits the Gruber-Mullins-Pokrovsky-Talapov behavior at the facet edge.
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Chikao Kawabata, Takamitsu Nakanishi
1990 Volume 59 Issue 11 Pages
3835-3838
Published: November 15, 1990
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Photographs of high
Tc copper-oxide Tl-, Bi-, Y-, Eu- and Nd-superconductors taken by a high-resolution transmission electron microscope were analyzed using an image processing computer. We found that the critical temperature
Tc follows a linearlike dependence versus spacing
d between Cu–O (or other elements) sheets for the
c-axis in a perovskite structure within a spacing range of 3∼4 Å. Our empirical formula is consistent with many experimental results for copper-oxide high
Tc materials discovered so far. We predict that a universal line for
Tc vs
d exists. We obtained critical spacing
dc of superconducting phase transition. We also propose a method of creating new copper-oxide higher
Tc materials.
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Nobuo Môri, Hiroki Takahashi, Yuichi Shimakawa, Takashi Manako, ...
1990 Volume 59 Issue 11 Pages
3839-3842
Published: November 15, 1990
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The pressure dependence of
Tc for the superconducting Tl–Ba–Ca–Cu–O compounds has been measured. It is found that the pressure coefficients of
Tc in Tl
2Ba
2CaCu
2O
8 change the sign from positive to negative with a maximum
Tc and that the highly hole-doped Tl
2Ba
2CuO
6 compounds show a large negative value of d
Tc⁄d
P. These results revealed a new feature of the pressure dependence of
Tc in the hole-doped superconductors and can be interpreted speculatively in terms of the hole concentration in the CuO
2 planes assuming that the carrier concentration is redistributed with pressure.
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Yuichi Akahama, Mototada Kobayashi, Haruki Kawamura
1990 Volume 59 Issue 11 Pages
3843-3845
Published: November 15, 1990
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The superconducting transition temperature,
Tc, of group-IV transition metal zirconium has been studied as a function of pressure up to 50 GPa in relation to the pressure-induced structural phase transition. Corresponding to a phase transition from hexagonal to bcc structure, a discontinuous increase of the
Tc is observed at 30 GPa. For the bcc phase, a high
Tc of 11 K has been developed. The result suggests that an electronic configuration similar to that of the bcc Nb is induced in the bcc phase as a result of an increase in valence
d-electron numbers by the
s-
d electronic transformation. The observation of the high
Tc is decisive experimental evidence for a pressure-induced transformation from group-IV transition metal to group-V transition metal.
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Takashi Imai, Kazuyoshi Yoshimura, Takashi Uemura, Hiroshi Yasuoka, Ko ...
1990 Volume 59 Issue 11 Pages
3846-3849
Published: November 15, 1990
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The
63Cu nuclear spin-lattice relaxation rate 1⁄
T1 has been measured for oriented powders of La
2−x(Sr, Ba)
xCuO
y in a wide concentration range. The spin dynamics in a lightly doped nonsuperconductor, La
1.96Sr
0.04CuO
4.02, is found to be qualitatively similar to that of a moderately doped high
Tc superconductor, La
1.85Sr
0.15CuO
4.03. The antiferromagnetic correlation length in the latter is estimated to be reduced by a factor of ∼2. The normal state spin dynamics has been successfully observed down to liquid helium temperature for La
1.88Ba
0.12CuO
4.00. The result showed a monotonous decrease of 1⁄
T1 with somewhat sublinear temperature dependence below 100 K.
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Masao Nomura
1990 Volume 59 Issue 11 Pages
3851-3860
Published: November 15, 1990
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Higher 3
n-
j symbols of the quantum group
SUq(2) are exploited such that relations for 3
n-
j symbols of
SU(2) could persist with slight modification. Kinds of relations for 3
n-
j symbols (
n=1, 2, 3, 4, 5) specific to the theory of
SUq(2) are presented.
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Shozo Takeno
1990 Volume 59 Issue 11 Pages
3861-3867
Published: November 15, 1990
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A pure one-dimensional anharmonic lattice with quartic lattice anharmonicity and nearest neighbour interactions is shown to exhibit a
p-like stationary self-localized mode. This is an intrinsic nonlinear mode with eigenfrequency higher than that of an
s-like mode to which attention has been focussed so far. Tking the displacement differences between nearest neighbour pairs of atoms as relevant field variables leads to a much simpler formulation as compared to the case of the
s-like mode. By introducing lattice Green’s functions and using a rotating-wave approximation (RWA), analytical expressions are obtained for the eigenfrequency and eigenfuntions for a
p-like mode appearing far above the harmonic frequency band. The RWA itself is also examined to show that it is a good and working approximation procedure for anharmonic-localized-mode problems.
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Takashi Nagatani
1990 Volume 59 Issue 11 Pages
3868-3875
Published: November 15, 1990
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Laplacian growth at reaction surface is considered to study the effect of surface reaction on the diffusion-limited aggregation (DLA). A two-parameter renormalisation-group method is developed to investigate the crossover phenomenon between the reaction-limited aggregation and the diffusion-limited aggregation. The global flow diagram in the two-parameter space is obtained. it is found that there are two nontrivial fixed points, the Eden point and the DLA point. The Eden point presents the reaction-limited aggregation. The DLA point corresponding to the DLA fractal is stable in all directions, while the Eden point is a saddle point. When the reaction rate is small, the aggregate crosses over from the dense structure on small length scales to the DLA fractal on large length scales. When the order m of reaction is not equal to one, the concentration of diffusing particles has an important effect upon the crossover.
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Masaki Hayashi, Juan J. Salazar
1990 Volume 59 Issue 11 Pages
3876-3885
Published: November 15, 1990
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We consider the d-dimensional invariant phase space for a quantum ideal relativistic gas and derive the cluster decomposition for the grand canonical and canonical partition functions as well as for the microcanonical and grand microcanonical densities of states. The cluster decomposition for the latter density of states is rederived on the basis of the (anti-)symmetrization of the quantum states. As an application of the formalism for the ideal (without interaction) gas to the case of systems with interaction we choose the statistical bootstrap equation and study the effects of the dimensionality in such statistical bootstrap systems together with those of the quantum statistics.
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Takashi Ishino, Riichiro Saito, Hiroshi Kamimura
1990 Volume 59 Issue 11 Pages
3886-3897
Published: November 15, 1990
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A general treatment of the symmetry for quantum spin systems is presented with the use of permutational operators. Symmetry operations which are commutable with a Hamiltonian form the symmetry group. Complete sets of spin functions which are specified by the total spin (
Stot) are projected onto the irreducible representations of the symmetry group, using the character table. We show from symmetry consideration that a minimum dimension exists for the ground state of the Heisenberg Hamiltonian with finite N spins. The diagonalization of the Hamiltonian with the use of symmetry consideration can be effectively performed for the complete sets of
Stot=0 by the method proposed in this paper. Numerical results of the ground state and all the excited states of
Stot=0 are presented for spin systems up to
N=20.
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Takayasu Tanaka
1990 Volume 59 Issue 11 Pages
3898-3903
Published: November 15, 1990
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A simple one-dimensional model of rough film surfaces on a substrate, in which unit square “atoms” are put at ramdom on a line “substrate” subdivided into unit cells is studied statistically. One of the fractal dimension of asperity of the film surfaces, the average surface length of clusters as a function of its given bottom length, is rigorously obtained. The calculated value of this fractal dimension for the above-mentioned model is approximately equal to
b⁄(
b+\sqrtπ\bar
n) and is smaller than 1.00 for a large average thickness \bar
n and a bottom length
b. But this result disagrees with the result, 1.05, obtained by Nakamura by means of computer simulation [Phys. Rev. B
40 (1989) 2549]. But, assuming that the deposits are nonuniform and composed of an ensemble of deposits with various average thicknesses, the fractal dimension of the simulation can well be explained.
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Setsuo Ichimaru, Shuji Ogata, Aiichiro Nakano
1990 Volume 59 Issue 11 Pages
3904-3915
Published: November 15, 1990
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Hydrogen nuclei in metal hydrides have a dual character of quantum solids trapped between the metal-lattice sites and of semiclassical itinerant particles diffusive through them. First-principles calculations are presented for the pycnonuclear reaction rates in binary-ionic mixture solids and for the thermonuclear reaction rates enhanced by quantum and classical many-body effects in itinerant hydrogen. The latter effects are elucidated through an elaborate Monte Carlo simulation study for short-range correlations between itinerant hydrogen, interacting via electron-screened repulsive forces, in periodic and aperiodic (due to defects) lattice fields of metal hydrides. We find that the screening potentials and the resultant fusion rates depend extremely sensitively on microscopic details in the lattice fields, corroborating qualitatively the varied results in recent “cold fusion” experiments.
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N. L. Singh, S. Agarwal, J. Rama Rao
1990 Volume 59 Issue 11 Pages
3916-3924
Published: November 15, 1990
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Excitation functions of (α,
xn yp zα) reactions on
93Nb and
169Tm have been measured upto 50 MeV by stacked-foil activation technique with a view to improve the quality of data in the case of
169Tm, which was earlier measured with a poor resolution scintillation detector. Comparisons are presented with the predictions of three pre-equilibrium models (i.e. Exciton, Hybrid and Index Models). While for (α,
xn) type of reactions reasonably explainable pre-compound contributions are found, there seem to be indications of direct inelastic scattering effects in (α, α
xn) type of reactions in medium and heavy nuclei.
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Yoshifumi Sakamoto
1990 Volume 59 Issue 11 Pages
3925-3930
Published: November 15, 1990
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Behaviour of alkali-halide microclusters (MX)
n at finite temperatures is investigated by Monte Carlo simulation for sizes
n=4, 8 and 18. The occurrence of the first-order phase transitions between solid-, liquid-, and gas-like phases is indicated, and the aspect of liquid-like clusters is discussed in detail. Furthermore, the binding energy of charged alkali-halide clusters [(MX)
nM]
+ for sizes from
n=60 up to 106 is evaluated via the optimization of atomic positions; a stepwise increase of the binding energy per particle with
n is found. The correlation with an experimental SIMS spectrum of [(CsI)
nCs]
+ is also discussed.
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Toshirou Kasuya, Masayoshi Tanaka, Akio Komori, Yoshinobu Kawai
1990 Volume 59 Issue 11 Pages
3931-3936
Published: November 15, 1990
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Subharmonic waves of electron plasma waves are observed in an electron beam plasma system and the parametric dependences of the waves are examined in detail. The excitation mechanism is also discussed.
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Hideo Sugama, Masahiro Wakatani
1990 Volume 59 Issue 11 Pages
3937-3951
Published: November 15, 1990
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An eddy viscosity model describing enstrophy transfer in two-dimensional turbulence is presented. It is similar to that of Canuto
et al. [Phys. Fluids
30 (1987) 3391] and provides an equation for the energy spectral function
F(
k) as a function of the energy input rate per unit wavenumber, γ
s(
k). In the enstrophy-transfer inertial range,
F(
k)∝
k−3 is predicted by the model. Our model is applied to the interchange turbulence of a plasma in shearless magnetic field. Numerical simulation demonstrates that the energy spectrum for high wavenumbers is well described by this model. The turbulent transport driven by the interchange turbulence is expressed in terms of the Nusselt number Nu, the Rayleigh number Ra and the Prantl number Pr in the same manner as that of thermal convection problem. When we use the linear growth rate for γ
s(
k), our theoretical model predicts that Nu∝(Ra·Pr)
1⁄2 for a constant background pressure gradient and Nu∝(Ra·Pr)
1⁄3 for a self-consistent background pressure profile with the stress-free slip boundary conditions.
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Shinji Koide
1990 Volume 59 Issue 11 Pages
3952-3961
Published: November 15, 1990
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A non-linear numerical simulation of the dynamo effect of a reversed field pinch (RFP) with finite beta is presented. It is shown that the
m=−1,
n=(9, 10, 11, …, 19) modes cause the dynamo effect and sustain the field reversed configuration. The role of the
m=0 modes on the dynamo effect is carefully examined. Our simulation shows that the magnetic field fluctuation level scales as
S−0.2 or
S−0.3 in the range of 10
3<
S<10
5, while Nebel, Caramana and Schnack obtained the fluctuation level is independent of
S for a pressureless RFP plasma.
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Hiroaki Ogawa, Satoshi Kasai, Hiroshi Tamai, Hisato Kawashima, Yoshihi ...
1990 Volume 59 Issue 11 Pages
3962-3976
Published: November 15, 1990
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In JFT-2M, impurity behaviors during the H-mode were studied by the spectroscopic method. During the H-mode without Edge-Localized Modes (ELMs), emissions of highly ionized ion lines increased with time, although emissions of less ionized ion lines decreased just after the H-mode transition and kept constant with time. It was found from time behavior of emissions of impurity ion lines and the iron-ion density profiles that not only metal impurity but also light impurity accumulated near the plasma center during the ELM-free H-mode. During the H-mode with ELMs, the impurity accumulation was relaxed by the onset of this instability compared with the ELM-free H-mode.
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Masaki Goda, Tadashi Takemori, Haruhiko Kubo, Tohru Ogawa
1990 Volume 59 Issue 11 Pages
3977-3988
Published: November 15, 1990
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We give a rigorous proof that the cyclic self-similar deflationary structure of the type discussed in the previous paper underlies a certain wider class of shifted Fibonacci sequences. The proof is equivalent to showing that an initial phase of the type θ
0=
r1+
r2⁄τ (τ=golden mean,
r1,
r2=rational numbers) is expanded into a recurring alternating power series of 1⁄τ (including finite alternating one). Recurring decimal series expansion in powers of other irrational numbers is also mentioned. For completeness, we also show that a pair of “least units of cycle” is automatically generated on deflation in the case of Fibonacci sequences that extend in both directions.
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Hidetoshi Konno
1990 Volume 59 Issue 11 Pages
3989-4003
Published: November 15, 1990
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Surface acoustic wave (SAW) parametric oscillation is studied with the use of the nonlinear Mathieu equation:
utt+
Kut+(
A+
B sin 2ω
t)
u+
Cu3=0, which can be derived from the nonlinear wave equation in a piezoelectric solid. The nonlinear model exhibits the various experimental features of SAW parametric oscillation: (i) the excitation of the 1/2 subharmonic mode, (ii) the frequency dependence of the amplitude and the linear growth rate and (iii) the saturation of the amplitude, which have been observed in LiNbO
3. Necessary condition for chaos and effect of dissipation upon the onset of chaos for the single mode model is also clarified.
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Masahiro Nakazato, Nobuyoshi Wakabayashi, Yoshichika \={O}nuki
1990 Volume 59 Issue 11 Pages
4004-4009
Published: November 15, 1990
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Intermetallic compounds RCu
6 (R=Pr, Nd and Sm) have phase transitions from the structures having orthorhombic symmetries to those of monoclinic symmetries at low temperatures. The monoclinic angles, γ’s, for these compounds have been measured as functions of temperature down to 1.5 K. The γ’s for PrCu
6 and NdCu
6 have monotonic temperature variations that could be reproduced by a simple mean field theory for the order parameter. The γ for SmCu
6 was unusual in that it has a maximum at about 20 K, suggesting the coupling between order parameter and the electronic states. The temperature dependence of the unit cell volume of SmCu
6 has been found to exhibit a significant decrease below about 120 K. These results have been analyzed on the basis of a coupling of the lattice to a two level system with a level separation of about 23 K.
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Kêitsiro Aizu
1990 Volume 59 Issue 11 Pages
4010-4021
Published: November 15, 1990
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The number of order parameters is assumed to be two, denoted by
Q and
Q*. The degree of anisotropy of the free energy function,
Φ, in its gradientless part is assumed to be 2α with α as an integer ≥2. The preceding paper [J. Phys. Soc. Jpn.
58 (1989) 2817] clarified that, when all Lifshitz terms are forbidden, a term expressed as (
Qα+
Q*α) or (
Qα−
Q*α)×(
Q*∂
zQ−
Q∂
zQ*) can exist in
Φ and can generate semicommensurateness. Following this paper, the present paper clarifies, on the assumption of α=2, that, when all Lifshitz terms and all terms of the type described above are forbidden, a term expressed as
(
Q−
Q*)(
Q*∂
xQ−
Q∂
xQ*)−i(
Q+
Q*)(
Q*∂
yQ−
Q∂
yQ*)
can exist in
Φ and can generate semicommensurateness. This clarification is performed by studying the 4⁄
mmm-
Eu case. A case of
three order parameters is also studied.
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Kenji Tashiro, Naoyuki Ozawa, Ko Sugihara, Takuro Tsuzuku
1990 Volume 59 Issue 11 Pages
4022-4028
Published: November 15, 1990
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By means of the AC-calorimetric technique, the specific heats of well-defined specimens of highly oriented pyrolytic graphite and its stages-1, -2, and -3 intercalation compounds with ICl have been investigated at temperatures down to 2.2 K. The apparatus was calibrated through a comparison of the data for pristine graphite with those in past studies. The specific heat in the range 2.2–5 K is represented, in an approximation, as a sum of electronic and lattice terms (γ
T and α
T3) for pure graphite, and additionally of an extra term due to the dispersionless optical-mode vibration of ionized ICl species in the compounds. γ and α both increase steeply with the ICl concentration, reflecting a monotonous increase of positive holes and softening of the lattice in the
c-direction respectively. A phenomenological theory, which correlates the lattice term to the elastic constants
C33 and
C44, turns out that α tends to decrease with increasing temperature.
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Masaru Aniya, Michisuke Kobayashi, Hideo Okazaki
1990 Volume 59 Issue 11 Pages
4029-4034
Published: November 15, 1990
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A statistical mechanical basis is given to the liquid-like model of superionic conductors which has been proposed recently by the authors. It is shown that the heavy ion mass introduced ad hoc in the previous reports to characterize the immobile lattice ions, is related to the mean square displacement of the lattice ion and to the coarse graining time which appears in the time averaging operation. The idea underlining in the liquid-like model, objective, immediate application and further direction are also discussed.
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Kazuyuki Matsumoto
1990 Volume 59 Issue 11 Pages
4035-4040
Published: November 15, 1990
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By the mean-field approximation, the Stipdonk and Hetherington’s (SH) model which explains the magnetism of solid
3He may undergoes two successive phase transitions at
Hex=0, where
Hex is a external field. However, we observed only one phase transition experimentally, that is the paramagnetic phase (PARA) to the low field phase (LFP). To resolve this discrepancy between the theory and experiments, the Monte Carlo simulation have carried out for the SH model. We employ the “heat bath” algorithm to save computing time. Hence, a micro-computer becomes available for this simulation. Two samples, which contain 32 and 108 atoms, respectively, are simulated with periodic boundary condition. The magnetic susceptibility and the sub-lattice one are measured as functions of the temperature and the external magnetic field. From the result, we can conclude that this discrepancy is due to inaccuracy of the mean-field approximation. We have also determined the magnetic phase diagram, i.e. the phase boundaries of LFP–PARA and LFP-HFP(high field phase).
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Atsushi Ikawa, Hideo Fukutome
1990 Volume 59 Issue 11 Pages
4041-4048
Published: November 15, 1990
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We study the electronic and lattice structures of a single chain of randomly alloyed Se and Te (Se
1−xTe
x) by an INDO type semi-empirical model. The model explains the Te concentration dependences of the gap and the mean bond lengths observed in Se
1−xTe
x enclosed in channels of mordenite. The gap decreased with
x because Te has lone pair levels higher than those of Se though their σ
* levels are nearly at the same positions. The Se–Se and Se–Te mean bond lengths are increased by the intramolecular charge transfer from the lone pairs of the adjacent Te to the σ
* orbitals of these bonds. The polarization effect of the σ bond due to adjacent Se contributes partly to the observed increase in the quadrupole splitting in
125Te Mossbauer spectrum.
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Chikara Sugiura, Wataru Konishi, Shizuko Shoji, Shinjiro Kojima
1990 Volume 59 Issue 11 Pages
4049-4053
Published: November 15, 1990
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The fluorine
Kα emission spectra in fluorescence from a series of alkaline-earth fluorides MF
2 (M=Mg, Ca, Sr and Ba) are measured with a high-resolution two-crystal vacuum spectrometer. An anomalously low intensity of the
K1L1 satellite peak arising from 1
s−1(2
s2
p)
−1 initial states is observed for SrF
2. The measured emission spectra are presented along with the UPS spectra of the F
− 2
p valence bands obtained by Poole
et al. and the fluorine
K absorption-edge spectra by Oizumi
et al. By using these spectra, the first peak or shoulder in the fluorine
K absorption-edge spectra is identified as being due to a core exciton which is formed below the bottom of the conduction band. The binding energy of the exciton is estimated to be 1.3(±0.3), 1.1(±0.2), 1.0(±0.2) and 1.7(±0.2) eV for MgF
2, CaF
2, SrF
2 and BaF
2, respectively.
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Hisatomo Harima, Akira Yanase, Akira Hasegawa
1990 Volume 59 Issue 11 Pages
4054-4064
Published: November 15, 1990
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The electronic energy band structure has been calculated for LaCu
6, a reference material for the heavy-fermion compound CeCu
6, by using a relativistic linearized APW method with the exchange-correlation potential in the local-density approximation. LaCu
6 is a compensated metal. It is shown that the Fermi surface consists of many electron and hole sheets in four bands, and holds a lot of the extremal cross sections in various directions. They can explain origins of the major experimental dHvA frequency branches reasonably well, but fails to agree with the experimental frequencies in the low frequency region, perhaps because of limitations of the MT approximation and/or the local density approximations. It is suggested that many dHvA signals may have been missed in the previous measurements.
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Makoto Yamashita, Norio Kawakami, Ayao Okiji
1990 Volume 59 Issue 11 Pages
4065-4073
Published: November 15, 1990
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The charge and spin excitation spectra in the degenerate Anderson model are calculated by means of the exact solution. We investigate a crossover behavior in the excitation spectra. When the
f-level position shifts from the valence fluctuation regime to the Kondo regime, the broad asymmetric peak structure in the charge excitation spectrum changes into the universal one around the bare
f-level position. In the case of the spin excitation, the spectrum gets narrower and forms the sharp Kondo resonance with the hump structure arising from the orbital degeneracy. The crystal-field effects on the spin excitation spectra are also investigated in the Kondo limit. As the crystal-field splitting is increased, the Kondo resonance gets narrower and the hump structure disappears.
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Yukio Tagawa, Naoshi Suzuki
1990 Volume 59 Issue 11 Pages
4074-4086
Published: November 15, 1990
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For the one-dimensional model system of the halogen-bridged mixed-valence metal complexes (HMMC) optical absorption spectra are calculated by taking into account the transition matrix elements. Particular attention is paid to optical absorption associated with electronic energy levels localized around solitons or polarons. It is shown that the intensity and the line shape of the absorption spectra depend strongly on the strength of the electron-lattice interaction. The obtained results are discussed in connection with the photo-induced midgap absorption spectra observed in HMMC.
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Katsukuni Yoshida
1990 Volume 59 Issue 11 Pages
4087-4095
Published: November 15, 1990
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The percolative conduction in a three-dimensional case was investigated for bulk specimens of Nb-alumina composites, where the dimensional crossover does not take place. The volume-fraction
f of Nb ranges from 0 to about 0.9. The percolation transition was found to occur around
f=0.15. This threshold value
fc implies a highly random structure of the composite. Such occurrence of the percolation transition and the behavior of the conductivity σ
* were described by an effective medium model in terms of an aggregation of the complex cells which can be regarded as structural elements of the networklike percolation cluster. The power law σ
*∝(
f−
fc)
μ was found to hold over the entire range
fc≤
f≤1 with a critical exponent μ=2.06±0.05, which closely approximates to the estimation given by the existing models.
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Tohru Morita
1990 Volume 59 Issue 11 Pages
4096-4102
Published: November 15, 1990
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We study a model fermion system on a lattice, which is expected to show the superconductor state, the normal state and the antiferromagnetic state, as we vary the number density of particles and the temperature. The phase transition between the superconductor state and the normal state is investigated in the “molecular-field approximation” with the aid of the cluster variation method.
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Michitaka Suzuki, Masashi Tachiki
1990 Volume 59 Issue 11 Pages
4103-4112
Published: November 15, 1990
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The magnetization processes in ferromagnetic superconductors such as ErRh
4B
4 are theoretically studied. Between superconducting electrons and localized spins, the
s-
f exchange interaction and the electromagnetic interaction are taken into account. On a basis of the theory, the unusual magnetization curves observed in ErRh
4B
4 are explained. Various types of magnetization processes are predicted to occur in ferromagnetic superconductors.
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Susumu Misawa
1990 Volume 59 Issue 11 Pages
4113-4120
Published: November 15, 1990
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On the basis of the
t-
J model, the normal-state Hall coefficient
RH at finite temperature and the superconducting transition temperature
Tc of the strongly correlated superconductors are calculated as functions of doping fraction δ, within the framework of the Hubbard-I-type decoupling-method of the Green’s functions and by using the expression for
RH derived by Fukuyama. The superconductivity-inducing
J is treated in a mean-field-like approximation and the normal-state
RH does not contain the contribution of
J. The obtained results are symmetrical with respect to hole and electron-doping. In the hole (electron)-doping case, the resultant
RH is positive (negative) for δ<1⁄3 and changes in sign at δ=1⁄3, and it varies in proportion to δ
−1 for small δ. These behaviors are compared with the experimental results of high-
Tc oxides.
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Masatoshi Imada
1990 Volume 59 Issue 11 Pages
4121-4128
Published: November 15, 1990
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The pairing susceptibility of the one-dimensional
t-
J model is examined numerically by the quantum transfer matrix method. The temperature dependence of the pairing susceptibility χ
s shows logarithmic behavior at low temperatures as χ
s∼α log
T for
T being the temperature. The coefficient α is determined as a function of
J⁄
t and the fillingness for
J and
t being the exchange interaction and the transfer. Beyond that of noninteracting fermions, α grows rapidly with the increase of |
J|.
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Akira Ochiai, Takashi Suzuki, Tadao Kasuya
1990 Volume 59 Issue 11 Pages
4129-4141
Published: November 15, 1990
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We have investigated the series of Yb pnictides with anti-Th
3P
4 structure. The valence of Yb varies from about 2 of Yb
4Bi
3 to 2.25 of Yb
4As
3 with the decreasing weight of the pnictogen. In the case of Yb
4As
3, the 4
f level is located around the band gap and the charge ordering below about 300 K has been observed. Further, in such a situation, we have observed a clear dense Kondo or heavy Fermion behavior in the resistivity, the magnetic susceptibility and the specific heat though the carrier concentration at 4.2 K is only about 0.001/Yb
3+ion. Yb
4As
3 is a new heavy Fermion compound which inquires whether the heavy Fermion state needs free carriers.
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Yoshitami Ajiro, Toshiya Inami, Hiroaki Kadowaki
1990 Volume 59 Issue 11 Pages
4142-4147
Published: November 15, 1990
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The universality class of successive magnetic phase transitions in the triangular lattice antiferromagnet CsMnI
3 is studied by measuring the critical exponent β using neutron scattering. A weak Ising anisotropy brings about two successive transitions at
TN1=11.2 K and
TN2=8.2 K which correspond to ordering of magnetic moments parallel and perpendicular to the c-axis, respectively. The critical exponents for the parallel and perpendicular components of the sublattice magnetization, β
⁄⁄=0.32±0.01 and β
⊥=0.35±0.01, are close to or in excellent agreement with the exponent for the three dimensional
XY symmetry of the order parameter in spite of the fact that the system has the Ising spin symmetry, in accord with a prediction. They remarkably differ from β=0.25±0.01 for CsMnBr
3 which has an XY anisotropy and belongs to the three dimensional
Z2×
S1 universality.
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Yoshihiro Ishibashi
1990 Volume 59 Issue 11 Pages
4148-4154
Published: November 15, 1990
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The polarization reversal in one-dimensional systems representing ferroelectrics has been studied on the basis of a proposed discrete lattice model. Latent nuclei are assumed to exist, and their influence on the polarization appearing in equilibrium states is discussed. Simulations of polarization reversal have been performed.
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Kazuo Gesi, Toshirou Yagi
1990 Volume 59 Issue 11 Pages
4155-4160
Published: November 15, 1990
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Effect of hydrostatic pressure on the phase transitions in the deuterated compound Ca
2Sr(C
2D
5COO)
6 has been studied in a pressure and temperature range of
p<550 MPa and −150°C<
T<50°C. The ferroelectric Curie temperature (4.7°C at 0 pressure; about 4 K lower than the one in the hydrogen compound) increases with increasing pressure with an initial pressure coefficient of 0.197 K/MPa. The II–III phase boundary is practically unchanged by deuteration. The effect of deuteration on the transition temperatures is described by a parallel depression of the Curie temperature by about 4.0 K.
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Kazutoshi Fukui, Tadaaki Saito, Shin-ichi Kondo, Yasuo Fujii, Yasuo Sa ...
1990 Volume 59 Issue 11 Pages
4161-4168
Published: November 15, 1990
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Core absorption spectra of crystalline (
c-) and amorphous (
a-) GeTe thin films have been measured in the 26–70 eV region. Photoemission spectra have also been measured to determine the binding energies of Ge 3
d and Te 4
d core levels. In the
c-phase Ge 3
d absorption shows excitonic peaks which can be explained in atomic picture, while Te 4
d absorption shows broad structures which reflect DOS of the conduction band. A small peak was found below the broad structures of Te 4
d absorption, the origin of which is the excitonic transition or the transition to the hole states generated by Ge vacancies located near the top of the valence band. In the
a-phase Ge 3
d absorption shows a broad structure while Te 4
d absorption somewhat sharp doublet. The difference in the spectral features in both phases suggests that the bonding character is more covalent in
a-GeTe than in
c-GeTe.
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Shinobu Takahashi, Masahiro Shirasaki, Masaaki Kobayashi, Akira Misu
1990 Volume 59 Issue 11 Pages
4169-4176
Published: November 15, 1990
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Piezoreflectivity spectra of KI were measured and energy shifts due to the cubic, tetragonal and trigonal deformations were obtained on the lowest energy exciton and the step which has been identified with the onset of a band to band transition. Energy shifts of the exciton were found similar to those of the step in the case of the uniaxial deformations. The similarity was reduced to the similarity of the electronic state, because of the large spin-orbit splitting of the 5
p state of an I
− ion. Difference in shift energy of the exciton and the step in the case of the cubic deformation was accounted for by changes of the effective mass and the high frequency dielectric constant. In addition, energy shifts determined directly from the piezoreflectivity were shown to be the same as those determined from the deformation induced changes of dielectric constants.
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Kunitsugu Soda, Hitoshi Hirashima
1990 Volume 59 Issue 11 Pages
4177-4185
Published: November 15, 1990
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A theoretical analysis is presented on the free energy of transfer from a solvent including vacuum to another one for solute molecules with variable conformations. All the interactions concerned in the transfer free energy are shown to be classified into two groups different in their nature: The one is composed of the intramolecular interactions of solutes where the shielding effect of solvent is included, and the other consists of various solvation effects characteristic of constituent atoms of each solute. Several assumptions implicitly taken in conventional analyses of the free energy of transfer between different solvents, are explicitly shown. It is described that formulas derived in this work will serve to determine more accurate atomic parameters on the solvation thermodynamics of biomolecules by comparison with experimental data.
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Isamu Nakata
1990 Volume 59 Issue 11 Pages
4186-4187
Published: November 15, 1990
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F. Lambert, R. Willox
1990 Volume 59 Issue 11 Pages
4188-4189
Published: November 15, 1990
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