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Nobuko Fuchikami, Hijiri Iwata, Shunya Ishioka
1999 Volume 68 Issue 12 Pages
3751-3754
Published: December 01, 1999
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To elucidate several issues relating to the thermodynamics of computations, we performed a simulation of a binary device using a Langevin equation. The simulation confirmed that the minimum energy consumption for a cycle of recording and erasing one-bit of information is kT ln 2 as suggested by Landauer. On the basis of our numerical results, we consider how to estimate the thermodynamic entropy of computational devices. We then argue against the existence of the so-called residual entropy in frozen systems such as ice.
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Ryoji Sahara, Hiroshi Mizuseki, Kaoru Ohno, Yoshiyuki Kawazoe
1999 Volume 68 Issue 12 Pages
3755-3758
Published: December 01, 1999
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A site-percolation model with two different sizes of particles is newly introduced on a square lattice. To estimate the fractal dimension and critical exponents with high accuracy, a finite-size scaling analysis is performed with a Monte Carlo simulation. The obtained fractal dimension coincides with that of the ordinary model, while the estimated exponents β, γ, and ν are slightly different from those of the ordinary model. However, the normalized exponents hat β = β / ν and hat γ = γ / ν remain the same as in the ordinary model, which is a manifestation of weak universality.
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Ryo Kanada, Kazuo Sasaki
1999 Volume 68 Issue 12 Pages
3759-3762
Published: December 01, 1999
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It is shown that the directed transport of Brownian particles can be induced by thermal ratchets with symmetric, two-state fluctuating potentials, contorary to an earlier belief that at least three states are needed for the potential to fluctuate if the potential is symmetric. It is proved that the potential must lack the symmetry of glide reflection in order for the directed movement of particles to occur in a two-state ratchet. Based on this finding, several models with symmetric potentials are constructed to demonstrate the occurrence of the particle flow.
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Tohru Kinugawa, Frederick J. Currell, Shunsuke Ohtani
1999 Volume 68 Issue 12 Pages
3763-3765
Published: December 01, 1999
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We propose the application of pulsed evaporative cooling, which has been used successfully for Bose-Einstein condensation of neutral atoms, to highly charged ions. Practically, this cooling technique can be highly efficient and favorable for ions in an electron beam ion trap (EBIT). By computer simulation, we have numerically estimated the performance of this cooling scheme on the basis of the standard evaporation theory. The result is very promising; from the initial temperature of 500 eV, Kr
+30 can be cooled to room temperature within a few seconds.
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Yasuhito Kiwamoto, Kiyokazu Ito, Akio Sanpei, Akihiro Mohri, Tetsumori ...
1999 Volume 68 Issue 12 Pages
3766-3769
Published: December 01, 1999
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We report new features observed in two-dimensional interactions of discrete vortices either isolated in vacuum or immersed in a background vorticity. The vortices are strings of electron plasma which are produced with a newly developed cathode array and trapped in a Malmberg trap. We observe long-lasting orbital motion of discrete vortices in vacuum, consistent with kinetic equations of point vortices, while a rapid re-organization occurs in the spatial distribution of vorticity when discrete vortices are immersed in an extended distribution of the background vorticity. The main features of the new observation are accounted for by a recently-proposed theoretical model incorporating collective interaction between two vortices.
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Kenichiro Yagi, Hikaru Terauchi, Noritaka Kuroda, Kazumasa Ueda, Toyon ...
1999 Volume 68 Issue 12 Pages
3770-3773
Published: December 01, 1999
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The structural properties of a neutral/radical 1 : 2 mixed compound, (NMe
4)
2TCNQ
3, are studied by the X-ray diffraction method in the temperature range between 25 and 150°C. The experimental data show that a second-order phase transition occurs at around 60°C and that the high-temperature phase has a monoclinic C2/m structure. The molecular planes of dimerized TCNQ
-· radicals, which slip against each other in the low-temperature phase, are expected from the C2/m symmetry to be totally eclipsed in the high-temperature phase. A good fit of the power law (1-T/T
c)^α to the temperature variation of the intensity of the Bragg reflection arising from the slipped radicals is obtained with T
c=330.7± 0.8 K and α =0.66± 0.05 for T≤ T
c. Influences of this novel phase transition on the electronic properties are discussed.
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Seishi Kondo, Tomoki Minoguchi
1999 Volume 68 Issue 12 Pages
3774-3777
Published: December 01, 1999
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We report, for the first time, on the dynamics of the contact angle in the process of quantum nucleation on a planar cell wall. The phase boundary of nucleus is assumed to be thin. Change of the contact angle causes the nucleus to deform and decrease to most 100f the imaginary part of action when Young's static contact angle is near 90°. This suggests that the dynamics of the contact angle has only a minor effect on critical overpressure Δ P
c if the static shape is close to hemispherical.
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Munehiro Nishida, Susumu Kurihara
1999 Volume 68 Issue 12 Pages
3778-3781
Published: December 01, 1999
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The quantum nucleation of phase slips in neutral superfluids confined in a thin torus is investigated by means of the collective coordinate method. We have devised, with numerical justification, a certain collective coordinate to describe the quantum nucleation process of a phase slip. Considering the quantum fluctuation around the local minimum of the action, we calculate the effective mass of the phase slip. Due to the coherence of the condensate throughout the torus, the effective mass is proportional to the circumference L of the torus, and the decay rate has a strong exponential L-dependence.
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Mitsuhiro Arikawa, Takashi Yamamoto, Yasuhiro Saiga, Yoshio Kuramoto
1999 Volume 68 Issue 12 Pages
3782-3785
Published: December 01, 1999
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The dynamical charge structure factor N(Q, ω) with Q smaller than the Fermi wave number is derived analytically for the one-dimensional supersymmetric t-J model with 1/r
2 interaction. Strong spin-charge separation in dynamics is found. N(Q, ω) with a given electron density does not depend on the spin polarization of a system with an arbitrary size. In the thermodynamic limit, only two holons and one antiholon contribute to N(Q, ω). These results together with generalized ones for the SU(K, 1) supersymmetric t-J model are derived via solution of the Sutherland model in the strong coupling limit.
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Fumio Komori, Kan Nakatsuji
1999 Volume 68 Issue 12 Pages
3786-3789
Published: December 01, 1999
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We studied the conductance of atomic-sized wires of iron made in a scanning tunneling microscope (STM) at 4.2 K. The conductance was measured as a function of the displacement between the iron substrate and the STM tip during the elongation and compression of the wires. The observed conductance curves were quantized, and some of the steps in the conductance curves display hysteresis for repeated displacements. The unit of the quantization is e
2/h as expected in ferromagnetic materials. A magnetic field of up to 150 mT hardly affects the conductance. These results are discussed in terms of the ballistic transport accompanied with the sudden atomic rearrangements and the continuous deformation around the wires.
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Yoshinori Konishi, Zhong Fang, Makoto Izumi, Takashi Manako, Masahiro ...
1999 Volume 68 Issue 12 Pages
3790-3793
Published: December 01, 1999
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Using the epitaxial strain, the magnetic and electronic phases can be controlled for thin films of the manganites, La
1-xSr
xMnO
3, grown on perovskite substrates with various lattice parameters. The strain-induced orbital-ordering (disordering) via coupling with the cooperative Jahn-Teller distortion produces different spin-structures, such as ferromagnetic, layer-type or chain-type antiferromagnetic states, and hence different magnetoelectronic characteristics. The spin-orbital phase diagram for La
1-xSr
xMnO
3 films has been obtained in the plane of strain-field (c/a ratio) vs doping x, which can be quantitatively reproduced by the density-functional electronic-calculation.
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Mitake Miyazaki, Keita Kishigi, Yasumasa Hasegawa
1999 Volume 68 Issue 12 Pages
3794-3797
Published: December 01, 1999
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We study the transition temperature T
c(H) of a quasi-one-dimensional (Q1D) superconductivity which is derived from the quantum effect of electron motion in a strong magnetic field. We calculate T
c(H) of both isotropic and anisotropic superconductivity by taking account of the optimal momentum of the Cooper pairs and the effect of higher harmonic terms along the second conducting axis in the tight-binding model. We find that, although T
c(H) of the spin-singlet superconductivity is strongly suppressed by the Zeeman effect, the suppression of T
c(H) is not very severe if we take the optimal pair-momentum and the higher harmonic terms into account. The obtained T
c(H) for the spin-singlet superconductivity is consistent with the experimental results in TMTSF salts.
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Yusuke Kato
1999 Volume 68 Issue 12 Pages
3798-3801
Published: December 01, 1999
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The Hall effect of a single vortex is studied within the time-dependent-Ginzburg-Landau (TDGL) theory taking into account both charging and screening effects explicitly. The effects of charging on the Hall conductivity are two-fold. One contribution is proportional to the charge density at the vortex center and the other enters the Hall conductivity through the local Hall electric field at the vortex center. The latter has been missed in earlier works and yields a Hall conductivity opposite in sign to that derived from the conventional argument using the TDGL equation with complex relaxation time.
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Masaki Kanada, Yukio Yasui, Masanori Ito, Hiroshi Harashina, Masatoshi ...
1999 Volume 68 Issue 12 Pages
3802-3805
Published: December 01, 1999
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The dynamical magnetic behavior of pyrochlore-type Tb
2Ti
2O
7 with geometrically frustrated magnetic moments has been investigated by means of neutron inelastic scattering on a single crystal specimen. Dispersion curves of the magnetic excitation and the temperature (T) dependence of the spectral function have been studied in detail, where we have identified the pattern of the short-range magnetic correlation and the T-dependence of the correlation length.
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Feng–Lin Shyu, Ming–Fa Lin
1999 Volume 68 Issue 12 Pages
3806-3809
Published: December 01, 1999
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The π-electronic excitations of the 3D (2D) multiwalled carbon nanotube bundles (arrays) are studied within the linear response approximation. The longitudinal dielectric function exhibits a peak or diplike structure at the neighborhood of ω =2γ
0 (γ
0 is the resonance integral). This special structure induces a pronounced π-plasmon peak in the loss function. The π-plasmon frequency and the oscillator strength of collective excitations are significantly affected by the direction and the magnitude of the transferred momentum, the number of shells in a multiwalled nanotube, and the dimensionalities of the coupled multiwalled nanotube systems. On the other hand, they are insensitive to the electronic structure of the single-walled carbon nanotube (or the chiral angle) and the slight change of the shell number. The predicted π-plasmon characteristics could be experimentally checked with EELS or optical spectra.
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Hideyuki Inouye, Koichiro Tanaka, Ichiro Tanahashi, Yuki Kondo, Kazuyu ...
1999 Volume 68 Issue 12 Pages
3810-3812
Published: December 01, 1999
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We observed an ultrafast response as fast as 240 fs in a gold nanoparticle system, in a femtosecond optical Kerr shutter experiment. We successfully demonstrate 2.5 THz optical switching. The ultrafast response of the Kerr signal is explained by a simple model taking into account the self-diffraction of the pump pulse by the generated transient grating.
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Takayasu Tanaka
1999 Volume 68 Issue 12 Pages
3813-3818
Published: December 01, 1999
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A method is presented to get a sustaining nonlinear inter-particle potential for an arbitrarily given steady motion in a one-dimensional nonlinear lattice. Here each particle is simply assumed to interact only with its nearest neighbors. This scheme is carried with an extensive use of formal series expansions and manipulations. In the latter half of this paper, this method is applied to some simple cases.
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Mikio Fujii
1999 Volume 68 Issue 12 Pages
3819-3825
Published: December 01, 1999
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The rate at which pure initial states satisfying the detailed balance condition on the photon number states deteriorate into mixtures in the decoherence process is computed for a laser field above threshold in the Scully-Lamb laser model. In steady-state laser operation, the field state suggested by Scully and Lamb is shown to be the least increase of the error area in the complex amplitude plane, thus becoming the most stable field state among the squeezed states characterized by the phase order parameter Δ .
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Yukiko Umeno, Heng Fan, Miki Wadati
1999 Volume 68 Issue 12 Pages
3826-3830
Published: December 01, 1999
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Exact integrability and algebraic Bethe ansatz of the small-polaron model with the open boundary condition are discussed in the framework of the quantum inverse scattering method (QISM). We employ a new approach where the fermionic R-operator which consists of fermion operators is a key object. It satisfies the Yang-Baxter equation and the reflection equation with its corresponding K-operator. Two kinds of `super-transposition' for the fermion operators are defined and the dual reflection equation is obtained. These equations prove the integrability and the Bethe ansatz equation which agrees with the one obtained from the graded Yang-Baxter equation and the graded reflection equations.
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Mizuhiko Saeki
1999 Volume 68 Issue 12 Pages
3831-3839
Published: December 01, 1999
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A general form of admittance is derived using the relaxation method under thermal equilibrium initial conditions from a second-order TCL equation with no external driving terms. Its admittance is shown to include the two interference terms in the TCLE method (method of TCL equations with external driving terms). Effects of the first and second interference terms in the TCLE method are numerically discussed for a quantal spin (magnitude 1/2) interacting with a spin-like bath and with a boson-like bath, respectively. It is shown that the first interference term which represents effects of the initial correlation and which is neglected in the relaxation method under decoupled initial conditions of the spin and bath, produces the effects which enhance the peaks of line shapes slightly and which abase the line shapes at the small frequency region, and becomes larger as the characteristic frequency of the heat bath becomes smaller.
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Miki Wadati, Takeya Tsurumi
1999 Volume 68 Issue 12 Pages
3840-3847
Published: December 01, 1999
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The ground state properties of a Bose-Einstein condensate with repulsive or attractive inter-atomic interaction confined in axially symmetric magnetic trap are studied through the variational approach. It is shown that, if the trap has a high asymmetry and thus the equi-potential surface of the trap is of “cigar” or “pancake” shape, the properties of the condensate are drastically changed from the case of isotropic (spherically symmetric) trap.
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Tomoyuki Nagaya, Takahiro Takeda, Hiroshi Orihara
1999 Volume 68 Issue 12 Pages
3848-3852
Published: December 01, 1999
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We have investigated the pattern fluctuation in a highly developed electro-hydrodynamic convection (EHC) by dynamic analyses of spatial Fourier coefficients of images. We measured the power spectrum and the two-time correlation function of spatial Fourier coefficients of images in the two turbulent states of EHC: the dynamic scattering mode (DSM)1 and DSM2 states. It was found that in the DSM1 state both the power spectrum and the correlation time show spatial anisotropy and have a characteristic peak at a wave number corresponding to the thickness of the cell in the rubbing direction. The peaks of the power spectrum and the correlation time decrease as the applied electric field is raised, and vanish entirely when the system undergoes the transition from DSM1 to DSM2. In the DSM2 state, there is no anisotropy in both the power spectrum and the correlation time.
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Yukitoshi Motome, Nobuo Furukawa
1999 Volume 68 Issue 12 Pages
3853-3858
Published: December 01, 1999
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A new Monte Carlo method is proposed for fermion systems interacting with classical degrees of freedom. To obtain a weight for each Monte Carlo sample with a fixed configuration of classical variables, the moment expansion of the density of states by Chebyshev polynomials is applied instead of the direct diagonalization of the fermion Hamiltonian. This reduces a cpu time to scale as O(N
dim2 log N
dim) compared to O(N
dim3) for the diagonalization in the conventional technique; N
dim is the dimension of the Hamiltonian. Another advantage of this method is that parallel computation with high efficiency is possible. These significantly save total cpu times of Monte Carlo calculations because the calculation of a Monte Carlo weight is the bottleneck part. The method is applied to the double-exchange model as an example. The benchmark results show that it is possible to make a systematic investigation using a system-size scaling even in three dimensions within a realistic cpu timescale.
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Nengwu Zheng, Tao Wang, Tao Zhou, Yujie Sun, Wei Su, Yi Zhang
1999 Volume 68 Issue 12 Pages
3859-3862
Published: December 01, 1999
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In this paper, a theory, called Weakest Bound Electron Potential Model Theory, is employed to study the transition probability of low states of Na, K, Rb and Cs. The parameters are determined by solving the coupled equations: concerning energy ε and the radial expectation value ‹ r›
nl of the weakest bound electron. Some transition probabilities of alkali metal atoms are given to show the reliability of the present method. The more accurate the ‹ r›
nl and energy ε, the better the calculated results of the transition probabilities.
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Hideki Hashimoto, Tomoyuki Shimonishi, Takeshi Miyazaki
1999 Volume 68 Issue 12 Pages
3863-3880
Published: December 01, 1999
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Vortex motions in a stably stratified rotating fluid are considered theoretically, based on the quasigeostrophic approximation. A class of exact staionary solution is obtained, which represents an ellipsoidal volume with uniform potential vorticity Q
0 embedded in a two-dimensional uniform strain field hat e with uniform background vorticity 2 hat γ . In a pure strain field ( hat γ =0), stationary solutions are allowed for | hat e /Q
0|< about 0.15. Similarly, stationary solutions are allowed for hat e /Q
0> about -0.1 in a simple shear flow ( hat γ = hat e ). We study the stability of these exact solutions against infinitesimal disturbances. In a pure strain field, highly elongated ellipsoids are shown to be unstable to Lame-modes whose order m is higher than 2. In a simple shear flow, a highly elongated ellipsoid whose major axis is perpendicular to the flow direction, is unstable, whereas any ellipsoidal vortex seems to be stable, if the major axis is parallel to the flow direction.
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Sergey Vladimirovich Vladimirov, Lennart Stenflo, Ming–Young Yu
1999 Volume 68 Issue 12 Pages
3881-3884
Published: December 01, 1999
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A renormalized quasilinear evolution equation for the particle distribution function in a weakly turbulent plasma is presented. The interaction of both resonant and nonresonant waves with the plasma particles is included. The nonresonant waves are crucial for the overall energy balance of the system and contribute significantly to the turbulent process. The velocity-space diffusion coefficients and turbulence levels of existing quasilinear theories are significantly modified.
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Juan A. Aparicio, Juan A. del Val, Victor R. González, Marco A. ...
1999 Volume 68 Issue 12 Pages
3885-3892
Published: December 01, 1999
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This work reports information about the temporal evolution of the excitation equilibrium departure in a high current pulsed arc. An argon plasma has been created in a linear lamp by discharging a capacitor bank on its electrodes. Spatially and temporally-resolved measurements have allowed us to determine electron density N
e and excitation temperature T with great accuracy. Single-wavelength interferometry and H_α-Stark broadening have been used to measure N
e (0.2--0.98× 10
23 m
-3). Excitation temperature has been obtained from Boltzmann-plot of ArII lines and ranges in this experiment from 13500 to 26500 K. By assuming this temperature is equal to kinetic electron temperature and by comparing the theoretically predicted and the experimental ArII/ArI intensities ratios at each instant of the plasma life, it is possible to measure the departure of the excitation processe from local them dynamic equilibrium (LTE) conditions and to show the ionizing characteristics of this close-to-LTE plasma. Different theoretical criteria have also been tested in order to select the minimal energy level from which partial LTE could be considered.
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Ruben A. Dilanian, Fujio Izumi, Kazuyuki Itoh, Takashi Kamiyama
1999 Volume 68 Issue 12 Pages
3893-3900
Published: December 01, 1999
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Structural changes accompanying a cubic-orthorhombic transition in K
2Mn
2(SO
4)
3 were investigated by high-resolution neutron powder diffraction. The structure parameters of cubic (P2
13) and orthorhombic (P2
12
12
1) phases were precisely refined by the Rietveld method with intensity data measured at 300 K and 40 K, respectively. In the cubic phase, sulfate ions exhibit dynamic orientational disordering. Six oxygen atoms surrounding each Mn
2+ ion form two kinds of highly distorted octahedra, whose degrees of distortion are remarkably different from each other. On the other hand, sulfate ions are fully ordered in the orthorhombic phase. We conclude that the distortion of the MnO
6 octahedra and short Mn-O distances in the cubic phase are closely related to the mechanism of the phase transition. Results of neutron diffraction experiments at 31 different temperatures support the idea that the orthorhombic → cubic transition proceeds via the nucleation and growth of the cubic phase within an orthorhombic matrix.
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Katsuki Katayama, Tsuyoshi Horiguchi
1999 Volume 68 Issue 12 Pages
3901-3910
Published: December 01, 1999
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We investigate the Ghatak-Sherrington model with S≥ 1, including S=∞, in a framework of the replica method, namely in terms of the replica symmetry (RS) solutions, the de Almeida and Thouless (AT) stability analysis and the one-step replica symmetry breaking (RSB) solutions. We find that there is a first order transition of van der Waals type between the paramagnetic phase and the spin glass phase and also a first order transition between the RS solution and the RSB solution in the model with integral S in some range of anisotropy parameter, while there is only a continuous transition in the model with half-integral S, including S=∞. We find that the model with integral S has a critical end point under the external magnetic field. We obtain phase diagrams as for the AT stability for the model under the external magnetic field.
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Takefumi Yamada, Fumihito Shikanai, Junko Hatori, Masaru Komukae, Tosh ...
1999 Volume 68 Issue 12 Pages
3911-3915
Published: December 01, 1999
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The effect of hydrostatic pressure on the phase transition of (CH
3)
2NH
2H
2AsO
4 was investigated by dielectric measurement at high pressure up to about 1.5 GPa. A pressure-induced phase for (CH
3)
2NH
2H
2AsO
4 was newly observed above 1.36 GPa at room temperature. The transition to the pressure-induced phase shows first order character. The effects of hydrostatic pressure on the ferroelectric transition temperatures for both crystals of (CH
3)
2NH
2H
2AsO
4 and (CH
3)
2N(H
0.5D
0.5)
2(H
0.5D
0.5)
2AsO
4 were dielectrically investigated. As the pressure increases, the transition temperatures for both crystals monotonously decrease. Their pressure derivatives, dT
c/dp, were obtained to be -49±1 K/GPa for (CH
3)
2NH
2H
2AsO
4 and -52±1 K/GPa for (CH
3)
2N(H
0.5D
0.5)
2(H
0.5D
0.5)
2AsO
4. From the present experimental results, the lack of an appreciable isotope effect on dT
c/dp was observed in (CH
3)
2NH
2H
2AsO
4.
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Hiroo Oya
1999 Volume 68 Issue 12 Pages
3916-3921
Published: December 01, 1999
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An anomalous peak has been reported at 1.8 K in the heat capacity/temperature curve of silver ultrafine particles (Ag UFP) of 20.7 nm in size. The effective strain η of Ag UFP was estimated to be 4.8 × 10
-4. This anomaly, however, cannot be explained within the harmonic approximation of lattice vibration. The sine-Gordon nonlinear partial differential equation was employed to explain the motion of the atoms in Ag UFP. A breather solution was chosen to express the lattice vibration of the Ag UFP. A value of exciting energy of the nonlinear lattice vibration was estimated from the data obtained in the experiment. A single nonlinear vibrator is considered to consist of Ag atoms in several 111 planes, and vibrate under mutual influence. Transition from nonlinear lattice vibration to linear one was also discussed.
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Tatsuma D. Matsuda, Yuji Aoki, Hitoshi Sugawara, Hideyuki Sato, Alexan ...
1999 Volume 68 Issue 12 Pages
3922-3926
Published: December 01, 1999
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We have measured the specific heat and magnetocaloric effect of an UCoAl single crystal down to --0.1 K in fields applied along the c-axis to investigate the thermodynamic aspects of the metamagnetic behavior. Hysteresis behavior observed in both physical quantities below --3 K confirms the first order character of the metamagnetic transition. We have found that an apparent decrease of the electronic part of specific heat C
e/T by 20% at 0.25 K with increasing field across the metamagnetic transition field of --1 T, evidencing the change in the density-of-states at the Fermi energy. C
e/T gradually decreases with increasing temperature in zero field. This anomalous temperature dependence can be explained by taking into account a spin fluctuation contribution in the low-field state.
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Yoshifumi Onishi, Kazumasa Miyake
1999 Volume 68 Issue 12 Pages
3927-3930
Published: December 01, 1999
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It is studied which type of superfluidity is induced by the paramagnon-mediated interaction in a two-dimensional isotropic Fermion system. The stability of various types of Cooper pairing is investigated in the framework of strong coupling theory on the basis of the RPA treatment for spin fluctuations. It is shown that the d-wave pairing is the most likely possibility in the two-dimensional isotropic Fermi system with short-range repulsive interaction. This is in marked contrast with the three-dimensional case where the triplet p-wave pairing is stabilized, and gives a prediction for a possible type of superfluidity of
3He adsorbed on the flat graphite surface.
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Hitoshi Furukawa, Tetsuo Ohmi
1999 Volume 68 Issue 12 Pages
3931-3935
Published: December 01, 1999
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The symmetry of Cooper pairs and transition temperature T
c of superfluid
3 He films thinner than coherence length with specularly reflecting boundary are investigated. Using the paramagnon model for the pairing interaction, we show the symmetry of pairs is likely p-wave and the gap at T
c is the ABM (or Planer) type. The quantum size effect yields the oscillating behavior of T
c as a function of the film thickness. On the contrary to the result of Tesanovic and Valls, the transition temperature we obtained is higher than that of the bulk system.
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Hiroshi Kawai, Yoshimichi Nakamura, Masatoshi Nakayama
1999 Volume 68 Issue 12 Pages
3936-3940
Published: December 01, 1999
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The time resolving dynamical Monte Carlo simulations(DMCS) on a narrow Si(001)S
B terrace are performed with the parameters obtained from the first-principles procedures. It is shown that the two-body time-correlation functions of the system correspond to those of the ideal kinetic one-dimensional Ising system. The dynamical feature of the flip-flop motion of dimers in the system is well described by the ideal kinetic one-dimensional Ising system. The one-dimensional kinetic transition rates on the system are obtained. The one-dimensional fluctuation of the system is enough slow to be observed by STM at realistic temperature.
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Tetsuro Saso
1999 Volume 68 Issue 12 Pages
3941-3947
Published: December 01, 1999
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A new approach is proposed which encompasses the dynamical mean field theory (DMFT) for strongly correlated electron systems and the self-consistent renormalization (SCR) theory of spin fluctuations. The latter is incorporated into DMFT as a O(1/d) correction, where d is the spatial dimensionality, but in a phenomenological way. The DMFT is completely recovered when the effect of spin fluctuation is omitted, whereas the properties at the quantum critical point (QCP) is the same as the SCR theory. An example of calculation is presented for the single band Hubbard model and the non-Fermi liquid behavior is demonstrated at QCP.
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Yusuke Wakabayashi, Nobuyoshi Wakabayashi, Masahiro Yamashita, Toshio ...
1999 Volume 68 Issue 12 Pages
3948-3952
Published: December 01, 1999
Released on J-STAGE: June 28, 2000
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X-ray scattering experiments have been performed on a quasi-one dimensional system, Ni
1-xPd
x(chxn)
2Br
3. Strong diffuse scattering was observed for x > 0.7, and it was interpreted as due to spatial inhomogeneity in the valence of metal ions. This inhomogeneity takes the form of CDW in which the metal ions within a chain have valences alternating between + 2 and + 4. Correlations in the valence sequence could be determined parallel as well as perpendicular to the chain direction. Pair correlation functions deduced from the measurements show the existence of strong correlation between the positions of bridging Br ions and those of Br counter ions. It is concluded that the valence of metal ions for x<0.7 is + 3. These results are consistent with previous data on optical and magnetic measurements.
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Etsuji Yamamoto, Yoshinori Haga, Yoshihiko Inada, Masao Murakawa, Yosh ...
1999 Volume 68 Issue 12 Pages
3953-3959
Published: December 01, 1999
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We grew a high-quality single crystal of UC and carried out the de Haas-van Alphen(dHvA) experiments. The Fermi surfaces of a semimetal UC were confirmed to consist of three ellipsoidal hole-Fermi surfaces centered at the X points and six cushion-like electron-Fermi surfaces centered at the W points in the fcc Brillouin zone. These Fermi surface properties are based on the combined results of dHvA experiments and SRAPW-energy band calculations. The hole and electron Fermi surfaces mainly originate from the C 2p valence band and the U 5f conduction band, respectively. The cyclotron mass of the hole is light, being a rest mass of an electron m
0, while the mass of the electron is heavy, being in the range from 4.0 to 15 m
0. The mass enhancement is large for the electron Fermi surface, originated from the U 5f character.
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Hiroaki Kusunose, Yoshio Kuramoto
1999 Volume 68 Issue 12 Pages
3960-3965
Published: December 01, 1999
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Entanglement of spin and orbital Kondo effect is investigated on the basis of a Kondo-type exchange model with twofold orbital degeneracy. By using Wilson's numerical renormalization-group method, we examine dynamical and thermal properties respecting the difference in time-reversal property of multipole operators. In the presence of particle-hole symmetry, the model has a new non-Fermi-liquid fixed point with a fractional entropy. The spectral intensity of the quadrupole susceptibility diverges in the zero-frequency limit, while the dipole susceptibility shows a Fermi-liquid-like behavior. This is understood by mapping to the two-channel Kondo model, in which the dipole moment is mapped onto the operators with the scaling dimension Δ
m=1, while the quadrupole moment onto the operators with another scaling dimension Δ
e=1/2. Even for a fairly particle-hole asymmetric case with the Fermi-liquid ground state, the non-Fermi-liquid behavior has significant influences in electric and thermal properties.
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Masahisa Tsuchiizu, Yoshikazu Suzumura
1999 Volume 68 Issue 12 Pages
3966-3974
Published: December 01, 1999
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The effect of an alternating potential on a one-dimensional half-filled Hubbard model with repulsive interaction has been examined by applying the renormalization group method to the bosonized Hamiltonian. The electronic state, which is determined by the competition between alternating potential and umklapp scattering, is calculated where the relevance and the irrelevance of the alternating potential lead to the band insulator and the Mott insulator respectively. The excitation gaps for charge and spin fluctuations are calculated for both states.
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Tsuyoshi Yamaguchi
1999 Volume 68 Issue 12 Pages
3975-3979
Published: December 01, 1999
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Electronic states of the impurity pentagon in carbon sheet are calculated by the DV-Xα-LCAO method. The neighboring C atom of the central pentagon is negatively charged and other C atoms are almost neutral. The electric field for a negative (positive) sample bias induces the electron transfer from the tail-end (central pentagon) C atoms of carbon sheet to the central pentagon (tail-end) C atoms. Both the occupied orbitals near the HOMO for the negative sample bias and the unoccupied orbitals for the positive sample bias have high charge density around the central pentagon. This well reproduces the scanning tunneling microscopy images.
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Takashi Sugiyama, Nobuo Tsuda
1999 Volume 68 Issue 12 Pages
3980-3987
Published: December 01, 1999
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The electrical resistivity ρ and the magnetic susceptibility χ were measured for the sintered samples of Ca
1-xLa
xRuO
3 (0≤ x≤ 1) (Lax) and Ca
1-xPr
xRuO
3 (x≤ 0.2). The temperature coefficient dρ/dT is positive at 300 K for all the samples, but ρ increases logarithmically with decreasing temperature as for the Kondo effect except for the end members x=0 and 1. The Curie-Weiss like χ was found for Lax, and the absolute value of the antiferromagnetic Weiss temperature increases with x until 0.3 and then decreases. For La 0.3 the Curie-type χ appeared overlapping the Curie-Weiss χ below 50 K, and there was no clear peak in χ down to 5 K. The resistance anomaly may have been caused either by the Kondo scattering, or a localization effect and/or an electron-electron interaction under the random distribution of hetero-valent cations.
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Chang–Ren Wang, Shui–Tien Lin
1999 Volume 68 Issue 12 Pages
3988-3993
Published: December 01, 1999
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The metal-insulator (MI) transition in Al
70Pd
22.5Re
7.5 quasicrystals with the resistivity ratio r=ρ
4.2 K/ρ
300 K ranging from 6 to 105 is identified by investigating the low-temperature conductivity and magnetoconductivity and analyzing the temperature behavior of W(T)= frac d
l nσ(T) d
l nT of the samples near the M-I transition. The extrapolated zero-temperature conductivity σ(0) for metallic samples near the M-I transition is found to vary as σ(0)=σ
0(1- frac r r
c )
ν with ν=1 and critical resistivity ratio r
c=12.8± 0.5. For weakly insulating Al
70Pd
22.5Re
7.5 quasicrystals, the conductivity σ(T) is seen to cross over from Mott's variable-range hopping dependence to the power-law temperature dependence.
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Tsuneya Ando, Takeshi Nakanishi, Masatsura Igami
1999 Volume 68 Issue 12 Pages
3994-4008
Published: December 01, 1999
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Effects of impurities with a strong and short-range potential are studied in carbon nanotubes within a k · p scheme. The calculated conductance approaches those obtained for nanotubes with a lattice vacancy when the strength of the potential is sufficiently large. The conductance at ε=0 is analytically shown to be quantized into zero, one, and two times of the conductance quantum e
2/π(h/2π) depending on the difference in the number of vacancies at A and B sublattices in nanotubes with a sufficiently large diameter.
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Takeshi Inaoka, Atsushi Nishida, Masayuki Hasegawa
1999 Volume 68 Issue 12 Pages
4009-4013
Published: December 01, 1999
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By means of the local-density-functional formalism, we examine the thickness dependence of carrier-electron states in doped semiconductor films with and without surface carrier-depletion layers. The film thickness is varied in a broad range where our carrier system evolves from a virtually semi-infinite (S-I) system to a quasi-two-dimensional (2D) one. The carrier-density distribution near the surface and the level of the chemical potential are found to remain the same as those of the S-I system down to such a small thickness that carrier motion normal to the surfaces is quantized significantly. With further decrease in film thickness, our carrier system evolves from the above S-I-like system into a quasi-2D one differently in the absence and presence of the depletion layers.
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Atsuo Satou, Yoshiko Oi Nakamura
1999 Volume 68 Issue 12 Pages
4014-4019
Published: December 01, 1999
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The ground state property of the alternating-spin ladder is studied in the case that the system involves an antiferromagnetic intra-chain interaction as well as two kinds of inter-chain interactions; one is between spins of the same magnitude and the other is between spins with different magnitudes. The calculation has been carried out by the exact diagonalization method. As a consequence of the competition among interactions, the system is revealed to show an interesting variety of phases in the ground state; the results are summarized as a phase diagram. A ferrimagnetic and two type of singlet ground states appear, and natures of two singlet phases are discussed.
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Masanori Ichioka, Kazushige Machida
1999 Volume 68 Issue 12 Pages
4020-4031
Published: December 01, 1999
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Focusing on La
2-xSr
xCuO
4, we study the stripe structure by the self-consistent mean-field theory of the Hubbard model. By introducing the realistic Fermi surface topology, the SDW-gapped insulator is changed to metallic. The solitonic features of the stripe structure and the contribution of the mid-gap states are presented. We consider the band dispersion, the local density of states, the spectral weight, and the optical conductivity, associated with the solitonic structure. These results may provide important information for the experimental research of the stripe structure, such as the angle-resolved photoemission experiments. The “Fermi surface” shape is changed depending on the ratio of the incommensurability δ and the hole density n
h. In real space, only the stripe region is metallic when δ/n
h is large.
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Takashi Fujikawa, Jun Kawai
1999 Volume 68 Issue 12 Pages
4032-4036
Published: December 01, 1999
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A simple theoretical approach is given to study XAFS-like spectra (extended X-ray emission fine structure, EXEFS) observed in X-ray fluorescence spectra based on one-step quantum mechanical formula derived by Almbladh and Hedin. Electronic relaxation and shake-off processes are crucial to explain the spectral features. Here the “shake-off” processes are different from those found in the typical XPS and XAFS spectra; the “shake-off” electrons are ejected during the fluorescence emission processes. Formal EXEFS formulas derived here are the same as the usually used XAFS formula. However, we should carefully use the phase shifts by taking account of the relaxation effects due to additional core hole production; they should be different from those used in the XAFS analyses. The radial dipole integral should be replaced by the corresponding monopole radial integral in the EXEFS analyses.
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Eiichi Yagi, Takafumi Sasahara, Tetsuo Joh, Marcus Hacke, Teruo Urai, ...
1999 Volume 68 Issue 12 Pages
4037-4044
Published: December 01, 1999
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In order to investigate the initial stage of Xe bubble formation in α-Fe, the lattice location of Xe atoms has been studied by the channelling method for the Fe crystals implanted with Xe ions at 150~keV at room temperature up to doses 10
14, 4× 10
14, 10
15 and 10
16~Xe/cm
2. Most of the Xe atoms are located at substitutional (S) and random (R) sites. At low implantation doses small portion of them are located at tetrahedral (T) sites and the sites slightly displaced from a lattice point by about 0.085~nm in the ‹ 111 › direction (D site). With increasing implantation dose the fractions of S-, D- and T-site occupancies decrease, whereas that of the R-site occupancy increases. These results suggest that at the initial stage of implantation Xe-vacancy (V) complexes, i.e., XeV, XeV
4 and larger ones, are formed and they act as nucleation centres for the subsequent growth to Xe bubbles.
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Tetsuji Konishi, Akihiko Kitada, Yoshiyuki Saito, Kimihisa Ito
1999 Volume 68 Issue 12 Pages
4045-4046
Published: December 01, 1999
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