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Saburo Kakei
1999 Volume 68 Issue 9 Pages
2875-2877
Published: September 01, 1999
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Orthogonal and symplectic matrix integrals are investigated. It is shown that the matrix integrals can be considered as a τ-function of the coupled KP hierarchy, whose solution can be expressed in terms of pfaffians.
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Hui–Hui Dai, Xianguo Geng
1999 Volume 68 Issue 9 Pages
2878-2881
Published: September 01, 1999
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The nonlinearization method of the Lax pair is developed and applied to the sine-Gordon equation, from which two new finite-dimensional completely integrable systems in the Liouville sense and some explicit solutions of this equation are obtained.
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Masaharu Isobe, Hiizu Nakanishi
1999 Volume 68 Issue 9 Pages
2882-2885
Published: September 01, 1999
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We performed numerical simulations on a two-dimensional inelastic hard disk system under gravity with a heat bath to study the dynamics of granular fluidization. Upon increasing the temperature of the heat bath, we found that three phases, namely, the condensed phase, locally fluidized phase, and granular turbulent phase, can be distinguished using the maximum packing fraction and the excitation ratio, or the ratio of the kinetic energy to the potential energy. It is shown that the system behavior in each phase is very different from that of an ordinary vibrating bed.
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Koh Saitoh, Tadahiro Yokosawa, Michiyoshi Tanaka, An Pang Tsai
1999 Volume 68 Issue 9 Pages
2886-2889
Published: September 01, 1999
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A model for the formation of an Al-Co decagonal quasicrystal with space group P overline 10 m2 from a τ
2-inflated monoclinic Al
13Co
4 approximant is constructed on the basis of the observation of high-resolution electron microscope images. It is shown that star- and crown-shaped structural units of the Al-Co decagonal quasicrystal are formed by combining elongated hexagon tiles or the basic structural unit of τ
2-Al
13Co
4.
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Hirofumi Kawanaka, Izumi Hase, Shunichiro Toyama, Yoshikazu Nishihara
1999 Volume 68 Issue 9 Pages
2890-2893
Published: September 01, 1999
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The magnetic properties of double perovskite oxide Sr
2FeWO
6 have been reported. The magnetic susceptibility and Mössbauer effect of
57Fe show that this compound is an antiferromagnet with T
N=37 K. The Mössbauer parameters below -- 20 K are the center shift of + 1.2 mm/s relative to metallic iron, the quadrupole splitting of 1.9 mm/s and the hyperfine field of -- 110 kOe. The quadrupole splitting has a strong temperature dependence. From these data, we conclude that Fe in Sr
2FeWO
6 is in the Fe
2+ high-spin state, while the hyperfine field seems to be quite small. The cell volume shows a large increase compared to other Sr
2FeTO
6 (T=Mo, Re, etc.), which is in the Fe
3+ high-spin state. These results suggest that these compounds have a strongly coupled charge and lattice systems.
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Osamu Takagi, Tetsuro Saso
1999 Volume 68 Issue 9 Pages
2894-2897
Published: September 01, 1999
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Linear conductance through a quantum dot is calculated under a finite magnetic field using the modified perturbation theory. The method is based on the second-order perturbation theory with respect to the Coulomb repulsion, but the self-energy is modified to reproduce the correct atomic limit and to fulfill the Friedel sum rule exactly. Although this method is applicable only to zero temperature in a strict sense, it is approximately extended to finite temperatures. It is found that the conductance near electron-hole symmetry is suppressed by the application of the magnetic field at low temperatures. Positive magnetoconductance is observed in the case of large electron-hole asymmetry.
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Masako Saito
1999 Volume 68 Issue 9 Pages
2898-2901
Published: September 01, 1999
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Impurity effects on spin-Peierls (SP) systems are investigated by using the phase Hamiltonian including mean field interchain interactions at T=0. It is shown that impurities induce antiferromagnetic long-range order and that there is a critical density, above which the SP lattice distortion disappears. Both first-order and second-order phase transitions are possible at this critical density. The former is realized in SP systems with a relatively large interchain interaction. Our results are qualitatively consistent with the recent experimental report on Cu(Mg)GeO
3 by Masuda et al. [Phys. Rev. Lett. 80 (1998) 4566.]
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Yutaka Maniwa, Hiroshi Kira, Fumihiko Shimizu, Youichi Murakami
1999 Volume 68 Issue 9 Pages
2902-2905
Published: September 01, 1999
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The structural and magnetic properties of potassium-loaded zeolite LTA, K
x-K
12Si
12Al
12O
48, were studied as a function of the loading density, x, up to -- 7. We observed a superlattice that develops with increasing loading density, and which is correlated with the low-temperature (T) magnetic phases. It was found that the ferromagnetic-like moment appearing at low T's coexists with lattice modulations such as the mass density wave or the charge density wave.
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Hiroyuki Nojiri, Hiroshi Kageyama, Kenzo Onizuka, Yutaka Ueda, Mitsuhi ...
1999 Volume 68 Issue 9 Pages
2906-2909
Published: September 01, 1999
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Various spin-gap excitations have been observed in the two-dimensional dimer system SrCu
2(BO
3)
2 by ESR. The zero-field energy gap of the lowest spin-gap excitation shows a splitting into two triplet modes and the energy splitting clearly depends on the magnetic field orientation. A zero-field splitting is also found between the S
z=+1 and S
z=-1 branches of each triplet. These behaviors are qualitatively explained by considering the anisotropic inter-dimer and intra-dimer exchange couplings. The averaged value of the lowest spin-gap energy is determined to be 722±2 GHz (34.7 K). We have also found a second spin-gap excitation at 1140 GHz (54.7 K), which indicates that the inter-dimer coupling is strong. Besides these modes, a number of gapped ESR absorptions are found and we propose that these excitations are caused by the localized nature of the excited state in the present system.
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Yuko Hosokoshi, Keiichi Katoh, Katsuya Inoue, Tsuneaki Goto
1999 Volume 68 Issue 9 Pages
2910-2913
Published: September 01, 1999
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We have newly synthesized organic radicals F
2PIMNH and Cl
2PIMNH, where F
2PIMNH = 2-[4
′-N-tert-butylamino-2
′, 6
′-difluorophenyl]- 4, 4, 5, 5-tetramethyl-4, 5-dihydro-1H-imidazol-1-oxyl and Cl
2PIMNH = 2-[4
′-N-tert-butylamino-2
′, 6
′-dichlorophenyl]- 4, 4, 5, 5-tetramethyl-4, 5-dihydro-1H-imidazol-1-oxyl. Both crystals include zigzag chains made of hydrogen bondings. The magnetism of Cl
2PIMNH is explained by the Heisenberg antiferromagnetic uniform chain model with 2J/k
B=-3.6 K and gapless ground state is suggested. On the other hand, static magnetic measurements of F
2PIMNH suggest the nonmagnetic ground state and the existence of a finite gap in its excitation spectrum. In this crystal, the next-nearest-neighbor contacts are seen, which are believed to be the origin of the energy gap.
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Yutaka Itoh, Takato Machi, Nobuaki Watanabe, Naoki Koshizuka
1999 Volume 68 Issue 9 Pages
2914-2917
Published: September 01, 1999
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We report nuclear quadrupole resonance (NQR) measurements of the
63Cu nuclear spin-lattice relaxation times in YBa
2(Cu
1-xNi
x)
4O
8 (x=0, 0.005, 0.010 and 0.020) using a spin-echo technique. We obtained the
63Cu NQR relaxation rate (1/T
1)
HOST due to spin fluctuations of the host Cu electrons and the Ni-induced
63Cu relaxation rate 1/τ
1 separately. The results demonstrate that the Ni impurities destroy the superconducting long-range order but not the pseudo spin-gap or the host Cu antiferromagnetic correlation.
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Tohru Fujita, Teruya Ishihara
1999 Volume 68 Issue 9 Pages
2918-2921
Published: September 01, 1999
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We observed the directional enhancement of photoluminescence (PL) for nonresonant excitation from cavity polaritons in the distributed feedback (DFB) waveguide microcavities when a cavity standing wave mode is resonant to an exciton. The cavities consist of a quartz grating substrate with --700 nm pitch, a (C
6H
5C
2H
4NH
3)
2PbI
4 film with large exciton oscillator strength, and a polystyrene film. They are regarded as a new type of one-dimensional photonic crystals consisting of resonant dispersive materials which couple strongly to modes in the crystals. On the other hand, a dye-dispersed film on the grating does not exhibit such an enhancement, which demonstrates that the polariton effect is essential. We point out for periodic structures in the strong coupling regime that a macroscopic polarization formed under a resonant condition may exhibit ultrafast radiative decay.
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Alexandru Popa
1999 Volume 68 Issue 9 Pages
2923-2933
Published: September 01, 1999
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We have demonstrated in previous papers the following property of closed, conservative and bounded systems: The energy which results from the Schrödinger equation can be rigorously calculated by line integrals of analytical functions, if the Hamilton-Jacobi equation, written for the same system, is satisfied in the space of coordinates by a periodical trajectory. In the present article, we show that this property is connected to the intrinsic wave properties of the system. This results from the equivalence between the Schrödinger equation and the wave equation, valid for conservative systems. As a consequence of the wave properties of the system, we show that the Hamilton-Jacobi equation has always periodical solutions, whose constants of motion are identical to the eigenvalues of the Schrödinger equation, written for the same system. It results that the calculation model presented in previous papers is generally valid in the case of closed, conservative and bounded systems. We present the applications of the model to the nitrogen and oxygen atoms, to the ions with the same structure, and to the He
2, Be
2 and B
2 molecules.
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Miaohua Chen, Hongliang Ma, Maosheng Li, Zhijun Chen, Wei , Fuquan Lu, ...
1999 Volume 68 Issue 9 Pages
2934-2935
Published: September 01, 1999
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The hyperfine structures of the transitions 4f
4(
5I)5d
6G
3/2→4f
4(
5I)6p
6H
o5/2, (577.21 nm) and 4f
4(
5I)5d
6G
3/2→4f
4(
5I)6p
6H
o5/2 (582.75 nm) of
143Nd II and
145Nd II have been measured by collinear laser-ion-beams spectroscopy. The hfs constants A and B of the involved levels have been determined.
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Chunguang Du, Zhaoyang Chen, Jingtao Zhang, Zhizhan Xu
1999 Volume 68 Issue 9 Pages
2936-2939
Published: September 01, 1999
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The effect of squeezed vacuum input on the optical bistable behavior of a system of N three-level atoms which are simultaneously coupled to a coherent pump field and a squeezed vacuum input is investigated. It is shown that the squeezed vacuum will significantly increase the range of the optical bistability, and the bistability can be controlled by the squeezing photon number and the strength of two-photon correlation.
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Tashpulat Rozi
1999 Volume 68 Issue 9 Pages
2940-2955
Published: September 01, 1999
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The purpose of this study is to examine the response of Hill's vortex to small three-dimensional disturbances of azimuthal numbers m=0, 2, 3 and 4. Specifically, we focus our attention on the temporal evolution of its surface shape. Moffatt and Moore (1978) used the streamfunction for the formulation of the problem for an axisymmetric disturbance (m=0), and obtained an approximate analytical solution for surface shape. To deal with three-dimensional modes, we must solve the Euler equation numerically inside the core. First, comparison is satisfactorily made, in the axisymmetric case (m=0), between the approximate analytical solution of Moffatt and Moore and the formulation using velocity potential in the entire space. Numerical computation for the disturbance with azimuthal number m=2 is performed. It is found that as time proceeds, double spike-like structure is formed around the rear stagnation point. We point out that some instability occurring near the front stagnation point, found in the previous paper, is due to the lack of number of terms in the expansion of the velocity field. Further numerical results for m=3 and 4 show that a peak of initial surface elevation moves downstream toward the rear stagnation point forming a m spike-like structure. A rough estimate suggests that the spikes grow with time t approximately as e
α m t, with α being dependent on initial condition, implying a fast development of fine-scale structure around the rear.
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Tatsufumi Nakamura, Susumu Kato, Tomokazu Kato
1999 Volume 68 Issue 9 Pages
2956-2961
Published: September 01, 1999
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The effect of plasma inhomogeneity on propagation of an intense and short laser pulse is examined analytically, especially in the case of a plasma with a constant density gradient. An envelope equation describing the laser pulse propagating through inhomogeneous plasmas is derived and solved analytically by using operator calculus. As a result, it is found that propagation of a laser pulse through a plasma with a constant density gradient is characterized by a unique parameter α=57κλ×P[TW] which depends on the plasma gradient κ, the laser wavelength λ, and the laser power P. With this parameter, we discuss self-focusing of laser pulses for realistic parameters. Necessary power to propagate the laser pulse for a desired distance without diffraction becomes clear by using our result.
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Takeshi Takaishi, Kyoji Nishikawa
1999 Volume 68 Issue 9 Pages
2962-2964
Published: September 01, 1999
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Linear dispersion characteristics of ion acoustic waves in a dusty plasma is studied in the fluid model. It is shown that charge variation of dust particles has a destabilizing effect of the wave in the short wavelength region where the electron Debye shielding of the ion space charge becomes incomplete. Secondary electron emission effect is also investigated and the charge variation is shown to have a destabilizing effect at all wavelengths except the longest one, if the dust particles are positively charged.
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Yasumitsu Matsuo, Keisuke Takahashi, Keisuke Hisada, Seiichiro Ikehata
1999 Volume 68 Issue 9 Pages
2965-2968
Published: September 01, 1999
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The proton dynamics along the c axis (the c
h axis) in the high-conductive phase for Rb
3H(SeO
4)
2 was investigated by the CW NMR analysis. It was found that the proton NMR line shape at room temperature was described in Gaussian curve but that it was described in the summation of the Gaussian and Lorentzian curves in the high-conductive phase. Moreover, the NMR line width in the high-conductive phase became 10 times narrower than that at room temperature. These results indicated that protons moved along the c
h axis in high-conductive phase. Furthermore, the dynamics of the protons along the c
h axis was made clear from calculating the second and forth moments. From this result, it was found that protons move disorderedly along the c
h axis between quasi-stable positions which exist between neighboring SeO
4 ions.
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Osamu Yamamuro, Mariko Ishikawa, Isao Kishimoto, Jean–Jacques Pi ...
1999 Volume 68 Issue 9 Pages
2969-2976
Published: September 01, 1999
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The heat capacity of plastically crystalline cyanoadamantane was measured with an adiabatic calorimeter in the temperature range 5--310 K. A glass transition appeared at 163 K in the supercooled plastic phase. The ordered phase obtained by annealing underwent a first-order transition to the plastic phase at 273 K. Enthalpy relaxation was also measured around T
g to investigate the molecular reorientation with long relaxation times (10
3 < τ <10
5 s). Dielectric permittivity of plastically crystalline isocyanocyclohexane was measured in the temperature range 120--230 K and frequency range 20--10
6 Hz to determine the relaxation times of the molecular reorientation. The fragility of cyanoadamantane was small while those of isocyanocyclohexane and cyclohexanol were intermediate between the fragile and the strong systems. The configurational entropies of these plastic crystals were calculated as functions of temperature. Their relaxation times were reproduced well by an extended version of the Adam-Gibbs theory which is modified by considering the configurational entropy inside the cooperatively rearranging region.
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Takao Yamamoto
1999 Volume 68 Issue 9 Pages
2977-2984
Published: September 01, 1999
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The relaxation processes of vicinal surface induced by the diffusion of adatoms along the step edge are analyzed by the Ginzburg-Landau-Langevin equation based on the harmonically-interacting step (HIS) picture. By the equation, the time evolutions of the step deformation width and the step fluctuation width are analyzed. For the relaxation process induced by the infinite-length step-edge diffusion, these quantities show the “universal” scaling behaviors. However, both of the universality and the scaling behavior disappear for the finite-length diffusion. To verify the results quantitatively, we performed the Monte-Carlo calculations for the solid-on-solid step terrace-step-kink model. The results from the Monte-Carlo calculations agree with the analytic results from the HIS picture very well.
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Youichi Ohno
1999 Volume 68 Issue 9 Pages
2985-2993
Published: September 01, 1999
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The electron-energy-loss spectroscopy (EELS) spectra of (Ca
xBi
1-xS)
1+yTiS
2 (x ≈ 0.5 and y≈0.2) and Mg
x(BiS)
1+y(TiS
2)
2 (x ≈ 0.04--0.07) are measured to study alkaline earth metal substitution and intercalation effects on the electronic structure of the first- and the second-stage misfit-layer compounds containing Bi. It is found that although a loss peak arising from a partial plasma resonance in a TiS
2 layer is still observed after large scale Ca substitution for Bi in a BiS layer, the electronic structure and optical properties are affected more significantly than those of the Mg intercalation derivative of the second-stage compound. Kramers-Kronig (K-K) analyses show that energy states for the Ca substitution compound are more delocalized and the optical window around 7.5 eV, which has been found for bulk TiS
2, disappears. For the Mg intercalation compound the joint density of states (JDS) is sharper due to an increased d/p energy gap and/or the localization of energy states in a direction perpendicular to layers.
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Yukihiro Shimizu, Alex Hewson, Osamu Sakai
1999 Volume 68 Issue 9 Pages
2994-2998
Published: September 01, 1999
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The specific heat and the magnetisation of an impurity Anderson model, which has a non-Kramers doublet lowest state of an f
2 configuration subject to the tetragonal crystalline electric field, are investigated using the numerical renormalization group method. We examine two cases where the ground states of the system are non-Fermi-liquid (NFL) of two-channel Kondo type model and local-Fermi-liquid (LFL), respectively. In the former case the temperature dependence of the specific heat shows a broad peak which has an entropy, 0.5ln 2, in the absence of the magnetic field. The specific heat shows two peaks in a very weak magnetic field: one has the same temperature dependence as in the absence of the magnetic field, the other at very low temperatures shows a release of the residual entropy, 0.5 ln 2. In the LFL case the specific heat shows only one peak which has an entropy, ln 2, in the absence of the magnetic field. The temperature dependence does not change in a very weak magnetic field. The γ-coefficient of the specific heat and the magnetic susceptibility never show - ln T dependence in the LFL case, even when the parameters are very close to the critical situation between NFL and LFL ground state.
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Youichi Yanase, Kosaku Yamada
1999 Volume 68 Issue 9 Pages
2999-3015
Published: September 01, 1999
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In this paper we study the effects of the strong coupling superconductivity on the normal state electronic structure. We point out that the pseudogap phenomena in High-T
c cuprates are naturally explained as a precursor of the strong coupling superconductivity. We expand the reciprocal of the T-matrix with respect to the momentum and the frequency, and we discuss the properties of the expansion parameters. We estimate these parameters and carry out the calculations for the single particle self-energy using the T-matrix and the self-consistent T-matrix approximations, respectively. We show that the superconducting fluctuations, which are strongly diffusive within the conventional weak coupling theory, become propagative and have the character of the pre-formed pairs in the strong coupling case. The spectral weight and the density of states show the gap-like features by the effects of the resonances with the thermally excited weakly-damped pre-formed pairs. The spectral weight at the Fermi energy is strongly suppressed. This suppression starts at the mean field critical temperature T
MF and the actual critical temperature T
c is strongly reduced owing to the fluctuations. These features properly explain to the pseudogap phenomena in High-T
c cuprates.
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Akinori Irizawa, Kazuyoshi Yoshimura, Koji Kosuge, Christian Dusek, He ...
1999 Volume 68 Issue 9 Pages
3016-3021
Published: September 01, 1999
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The layered compounds Ba
1-xBi
xCoS
2 (0≤ x≤ 0.7) were prepared in a single phase of the BaCoS
2 type. The electric resistivity was found to be drastically decreased with x and shows a systematic change from insulating to metallic with decreasing temperatures: the electric resistivity for x≥q 0.05 follows the T
2-dependence below 20 K, indicating that the Fermi liquid state is realized at low temperatures, while it shows semiconducting temperature dependence at high temperatures. The electronic specific heat coefficient γ for Ba
0.95Bi
0.05CoS
2 was estimated to be a small value of 3.5 mJ/mol·K
2 instead of the large T
2-term in the resistivity. In magnetic susceptibility measurements, the antiferromagnetic ordering was found to be stable even in metallic samples. These results can be understood as: two types of electronic bands near the Fermi level in the electron-doped BaCoS
2, one of which has the Mott-Hubbard gap giving rise to the antiferromagnetic ordering just as BaCoS
2 and the other has a small but finite size of density of states at the Fermi level, showing metallic conduction.
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Kiyoshi Itoh, Yuji Yano, Nobuo Tsuda
1999 Volume 68 Issue 9 Pages
3022-3026
Published: September 01, 1999
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The resistivity and the Seebeck coefficient were measured for sintered Ca
1-xNa
xPd
3O
4 (0≤ x≤ 1). There occurs a metal to insulator transition at x=0.3, and the material is nonmetallic for smaller x. The resistivity shows a logarithmic temperature dependence for x<0.3, and it is as low as 0.1 Ωcm at 300 K for CaPd
3O
4. When the resistivity of CaPd
3O
4 is analyzed with an activation type process, the activation energy becomes temperature dependent. The magnetic susceptibility of CaPd
3O
4 is as small as 2.9× 10
-5 emu/mol at 277 K and almost temperature independent. The transition is supposed to be a Mott-Anderson transition.
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Harukazu Yoshino, Keizo Murata
1999 Volume 68 Issue 9 Pages
3027-3033
Published: September 01, 1999
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It is known that the third angular effect of the magnetoresistance of quasi-one-dimensional (Q1D) metals for the field rotation within its most conducting plane is observed as a hump of the magnetoresistance when the magnetic field is almost parallel to the one-dimensional axis. In order to explain this hump, the angular dependence of the magnetoconductivity tensor of a Q1D conductor, (TMTSF)
2ClO
4, where TMTSF is tetraselenafulvalene, is numerically calculated by semiclassical relaxation time approximation. We demonstrate that the third angular effect is originated from the incomplete cancellation of the carrier velocity, v
z, over the closed and semi-closed orbits of carriers on the Q1D Fermi surface caused by weak Lorentz force. We also show that the oscillating angular dependence of the magnetoresistance reported for (TMTSF)
2PF
6 by the off-angle rotation of the magnetic field should be intrinsically, even for o rthorhombic systems, unsymmetric about the lattice plane including the rotation and the most conducting axes.
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Shunsuke Yoshii, Masatoshi Sato
1999 Volume 68 Issue 9 Pages
3034-3040
Published: September 01, 1999
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Various physical properties of Y
2-xBi
xRu
2O
7 have been studied. The critical temperature T
G of a spin-glass transition observed in the system decreases with x and goes to zero at x=x
c in the region of the insulator-metal phase boundary. The low temperature specific heat coefficient γ increases with decreasing x from 2.0, has a maximum at x
c and decreases with further decreasing x. In Y
2Ru
2O
7, there exists a significant specific heat anomaly at T
G. Because the anomaly does not depend on the applied magnetic field, it seems to be due to a structural phase transition, suggesting that the spin-glass transition is induced by this transition. By detailed studies on the relationship between the transport properties and the transition temperatures T
G of Y
2-xM
xRu
2O
7 (M=Bi, Lu and Ca) and Y
2Ru
2-xTi
xO
7, an intimate correlation of the itinerant nature with the structural transition is pointed out.
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Yoshiyuki Yoshida, Atsushi Mukai, Rikio Settai, Kousaku Miyake, Yoshih ...
1999 Volume 68 Issue 9 Pages
3041-3053
Published: September 01, 1999
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We measured the de Haas-van Alphen (dHvA) effect, magnetoresistance and specific heat to clarify the two-dimensional Fermi surface properties of Sr
2RuO
4. From the angular dependence of the dHvA amplitude, we determined the Yamaji angle for three quasi-cylindrical Fermi surfaces α, β and γ to be 30.6°for the Fermi surface α, about 30°for β and 15.3°for γ. The cyclotron masses of sum and difference oscillatory components, m
*β±α and m
*γ±α, are found to be highly different from m
*_β + m
*_α and m
*_γ + m
*_α, respectively, for any field direction. The dHvA oscillation due to sums and differences is not due to the magnetic interaction but to the chemical potential oscillation for quasi-two-dimensional Fermi surfaces. The specific heat data are discussed from a viewpoint of a characteristic energy gap in a possible p-wave superconductor Sr
2RuO
4.
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Yukihiro Okuno, Masashige Matsumoto, Manfred Sigrist
1999 Volume 68 Issue 9 Pages
3054-3061
Published: September 01, 1999
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The microscopic mechanism of circular currents induced in the vicinity of a non-magnetic impurity is analyzed for the (time-reversal symmetry breaking) chiral superconducting state d ( k ) = hat z (k
x ± i k
y) which is very likely realized in Sr
2RuO
4. From the analytic, not self-consistent solution of the Bogoliubov-de Gennes equations we find two types of quasiparticle states, a bound state and the continuum state. Through impurity scattering the condensate transfers angular momentum to the quasiparticle states which generate a circular current. At low temperature the continuum part of the quasiparticle spectrum gives the main contribution. The non-selfconsistent solution yields a state of finite angular momentum. The comparison with the corresponding Ginzburg-Landau theory reveals the existence of a compensating counterflow created by the superconducting condensate. The currents and magnetic fields appearing around the impurity have possibly been observed by muon spin relaxation measurements.
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Tomio Koyama
1999 Volume 68 Issue 9 Pages
3062-3068
Published: September 01, 1999
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We formulate a quantum theory for the transverse Josephson plasma in intrinsic Josephson junctions. The electromagnetic field is quantized in this formulation. The Josephson plasma is, then, described as the massive photon in superconductors. We derive the transverse dielectric function and calculate the plasma frequency at finite temperatures in the case where the superconducting energy gap has d
x2-y2-wave symmetry. The effect of thermally excited quasiparticles on the Josephson plasma is discussed. The temperature variation of the plasma frequency near T
c is strongly dependent on the interlayer coupling constants.
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Hiroshi Shimahara
1999 Volume 68 Issue 9 Pages
3069-3073
Published: September 01, 1999
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It is shown that the upper critical field of the superconductivity can be remarkably enhanced due to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) effect, even if the system does not have any flat portion of the Fermi-surface (FS). As an example, we examine a two-dimensional tight binding model at various hole concentrations. The optimum electron concentration at which the ratio of the critical field to the Pauli paramagnetic limit of the uniform BCS state takes maximum is found to be far away from the half-filling. Near there, the ratio exceeds 5 times the Pauli paramagnetic limit. We explain a new mechanism by which the critical field is enhanced due to an FS structure. The FFLO state is discussed in connection with the organic superconductors.
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Tatsuo Goko, Fumihiko Nakamura, Toshizo Fujita
1999 Volume 68 Issue 9 Pages
3074-3077
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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The anisotropic stress effects on superconducting temperature T
c have been investigated in single crystals of La
2-xSr
xCuO
4 with x=0.10 and 0.145. Utilizing non-hydrostaticity of the applied pressure, we estimated T
c in the tetragonal phase at the ambient pressure. The T
c was found to be higher in the tetragonal phase than the T
c in the orthorhombic phase. We demonstrate that the orthorhombic distortion suppresses superconductivity and the tetragonal structure with the flat CuO
2 plane is favorable for superconductivity.
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Kazuo Mukai, Kentaro Suzuki, Keishi Ohara, Javad B. Jamali, Norio Achi ...
1999 Volume 68 Issue 9 Pages
3078-3085
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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The magnetic susceptiblities, ESR and powder X-ray patterns of verdazyl radical alloy, (p-CDpOV)
1-x(p-BDpOV)
x (x=ox 0--1 ), were measured to study the doping effects of magnetic impurities for the quasi-1D Heisenberg ferromagnet (p-CDpOV) and antiferromagnet (p-BDpOV) with S = 1/2, which have similar van der Waals radius to each other. The susceptibility curves systematically change with impurity concentration x. The most noticeable point is that the impurity effect is rather mild on the 1D ferromagnetic Heisenberg system. The characteristic feature of 1D ferromagnet still survives even in the heavily doped sample with x = 0.50. The positive Weiss constant (θ) and the ferromagnetic intrachain exchange interaction (2J
intrachain) remain constant between x = 0 and 0.50. The results indicate that the p-BDpOV radical functions as an ideal dopant for the 1D ferromagnet, p-CDpOV. This is the first report of the effects of magnetic impurities on the quasi-1D ferromagnetic chain system.
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Yuuki Watanabe, Seiji Miyashita
1999 Volume 68 Issue 9 Pages
3086-3090
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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In order to study conditions for the appearance of ferromagnetism in a wide filling region, we investigate numerically three types of one-dimensional Lieb-ferrimagnetic Hubbard models: a periodic diamond (PD) chain, a periodic alternately-attached leg (PAAL) chain and an open diamond (OD) chain. All of these models have a flat band (or equivalently, degenerate single-electron eigenvalues). The PD and OD chains commonly have a local-loop structure. Nagaoka's theorem holds only in the PD chain. At half-filling, it have been rigorously proven that all of these models are ferrimagnet. Away from half-filling, however, quite different magnetic properties are found. In the fillings 1/3<ρ
e<1/2, the ground state of the PD chain for a infinitely-large U is the extended ferromagnetic state, that is, the saturated ferromagnetic state or the spiral state for odd or even number of electrons, respectively. In the PAAL chain, on the other hand, there is no magnetic order. Thus, the flat band is found to be not a sufficient condition of the extended ferromagnetic state. We find, moreover, that the saturated ferromagnetism appears in the OD chain, although the Nagaoka theorem does not hold on this chain. This indicates that the local-loop structure plays an important role on the appearance of the extended ferromagnetic state.
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Satoshi Kokado, Naoshi Suzuki
1999 Volume 68 Issue 9 Pages
3091-3094
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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Dynamical structure factors of S=1/2 antiferromagnetic--ferromagnetic alternating chains are calculated by the numerical method based on the ground state obtained by exact diagonalization procedure and also by the pair dynamical correlated-effective-field approximation. A couple of characteristic natures of neutron scattering intensity due to magnetic excitations are predicted: the intensity of transition to the lowest triplet states takes the maximum value at q=π/2 in the whole range of the exchange ratio, and the continuum states above the second gap could be observable at large q.
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Kazuo Gesi
1999 Volume 68 Issue 9 Pages
3095-3099
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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The dielectric properties have been measured for single crystals of ferroelectric (CH
3NH
3)
2AlBr
5 · 6H
2O. The dielectric constant along the a direction ε
a shows a sharp λ -type peak at the Curie temperature of 76.6 K below which the crystal shows ferroelectricity along the a direction. The dielectric constant along the a direction ε
a obeys a Curie Weiss law with the Curie constant of 3.3×10
2 K in a temperature range about 30 K above the Curie temperature. The spontaneous polarization approaches the saturation value of 6.5×10
-3 C/m
2 at low temperatures. Beside the ferroelectric Curie temperature, there is a first order phase transition at about 250 K where the dielectric constant shows a slight discontinuous change. The results are compared with those of the isomorphic ferroelectric crystal of (CH
3NH
3)
2AlCl
5 · 6H
2O, and discussed.
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Tsuyoshi Idé, Akio Kotani
1999 Volume 68 Issue 9 Pages
3100-3109
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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Theoretical study for Cu 4p-1s resonant X-ray emission spectroscopy (RXES) of Nd
2CuO
4 is given in the context of local and nonlocal natures of electronic excitations. Detailed analyses with an impurity Anderson model and multi-Cu models are presented, based on exact diagonalization technique. By investigating partial densities of states, basic characters of each excited state are clarified. It is demonstrated that a disagreement with experimental data is unavoidable with the impurity model. The key concept to solve the difficulty is Zhang-Rice singlet formation in the intermediate state of RXES. We find that it survives in the final state of RXES as the lowest charge-transfer excitation. The limitation of the impurity model and the essential role of nonlocal excitations in RXES are stressed.
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Shin–ichi Tadaki, Macoto Kikuchi, Yuki Sugiyama, Satoshi Yukawa
1999 Volume 68 Issue 9 Pages
3110-3114
Published: September 01, 1999
Released on J-STAGE: June 28, 2000
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The optimal velocity traffic flow model is one of the car-following models which describe the behavior of cars by differential equations. In that model, each car controls its speed toward an optimal (safety) velocity, which depends only on the headway. We constructed a new car-following type simulation model for traffic flow in a coupled map form based on the optimal velocity model. We can easily simulate open road systems with the model. The emergence of weakly congested flow induced by noise is investigated. We observe the enhancement of the car density induced by noise. The strong traffic jam hardly occurs in open road systems. We discuss the problems of unrealistic acceleration in the optimal velocity model and the possibility of spontaneous formation of strong traffic jams.
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Kiwamu Oda, Kiyohiro Sugiyama, Noriaki Kensho Sato, Takemi Komatsubara ...
1999 Volume 68 Issue 9 Pages
3115-3116
Published: September 01, 1999
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Dai Aoki, Tetsutaro Inoue, Koichi Kindo, Norihito Suzuki, Kousaku Miya ...
1999 Volume 68 Issue 9 Pages
3117-3118
Published: September 01, 1999
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Tatsuya Nagao, Jun–ichi Igarashi
1999 Volume 68 Issue 9 Pages
3119
Published: September 01, 1999
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1999 Volume 68 Issue 9 Pages
3120
Published: September 01, 1999
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1999 Volume 68 Issue 9 Pages
3121
Published: September 01, 1999
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