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Takao Yamamoto, Yo–ichi Kawashima
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2715-2718
Published: 2000
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We investigate the fluctuation properties of a multilayer membrane system by means of a capillary-wave (CW) picture.
We examine the non-crossing effect between membranes.
From the CW picture, we derive a novel Hamiltonian expressing the fluctuation properties, which is different from the Hamiltonian proposed by Helfrich [W. Helfrich: Z. Naturforsch
33a (1978) 305].
To verify the new Hamiltonian, we performed a Monte Carlo simulation on the basis of the Gaussian solid-on-solid model for a one-dimensional multilayer membrane system.
The result strongly supports the novel Hamiltonian.
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Syuji Miyazaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2719-2722
Published: 2000
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The mean square distance σ
2(t) of the diffusion induced by on-off intermittency is derived based on the continuous-time random walk theory. It obeys a scaling law σ
2(t)=2Dt φ(t/τ) with diffusion constant D and characteristic time τ, which is confirmed by the use of numerical iterations of a specific periodic map. The scaling function φ and the power spectrum of the on-off intermittency variable I(ω) are analytically obtained from the distribution function of the laminar duration. Normal diffusion (φ(z)∼ 1) and slow diffusion (φ(z)∝ 1/√z) are observed, respectively, for t>>τ and t<<τ. The former and latter correspond to the flat part (I(ω)∼ const) and the power law (I(ω)∝ 1/\sqrt{ω}), respectively, for the power spectrum.
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Masatoshi Imada, Tsuyoshi Kashima
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2723-2726
Published: 2000
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A numerical algorithm for studying strongly correlated electron systems is proposed. The groundstate wavefunction is projected out after a numerical renormalization procedure in the path integral formalism. The wavefunction is expressed from the optimized linear combination of retained states in the truncated Hilbert space with a numerically chosen basis. This algorithm does not suffer from the negative sign problem and can be applied to any type of Hamiltonian in any dimension. The efficiency is tested in examples of the Hubbard model where the basis of Slater determinants is numerically optimized. We show results on fast convergence and accuracy achieved with a small number of retained states.
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Tatsuzo Nagai, Kazuhiro Fuchizaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2727-2730
Published: 2000
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The relaxation process to a scaling state which is a nonequilibrium steady state in evolving cellular structures, such as soap froths and grain systems, is investigated by computer simulation of the vertex model and phenomenology in two dimensions. Our results are as follows: (i) This relaxation is hierarchical, that is, the average size of a cell (the characteristic length of the system) relaxes rapidly at an early stage and then topological quantities associated with the shape of cells relax slowly at a late stage. (ii) The latter slow relaxation is well described by the stretched exponential function. (iii) The time exponent β of the stretched exponential function is related to the power γ of the distribution for the time interval of the topological change in the form γ = 1 + β.
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Yusuke Wakabayashi, Youichi Murakami, Ichiro Koyama, Tsuyoshi Kimura, ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2731-2734
Published: 2000
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Orbital and charge ordering phenomena in bilayered perovskite manganite LaSr
2Mn
2O
7 have been studied by resonant X-ray scattering. Superlattice reflections corresponding to these orderings are observed below 210 K. The in-plane and stacking structure of the orbital and charge order is determined from these reflections. The anisotropy of the anomalous atomic scattering factor of Mn
3+ in the orbital ordered state is observed in the azimuthal angle dependence of the reflections. The anisotropy is attributed to the band dispersion of 4p level due to the layered structure as well as the orbital order. In the course of this study, we have found that charge and orbital orderings collapse simultaneously, maintaining the same correlation lengths with further decreasing temperature.
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Takeo Kato
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2735-2738
Published: 2000
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Soliton-pair nucleation rates Γ = A exp(-B) are studied in highly biased sine-Gordon systems with a local inhomogeneity for both a thermal activation regime and a quantum tunneling regime. It is found that the local inhomogeneity strongly affects the nucleation rates by modifying the bias-dependence of the exponent B. This change in the exponent B is explained by a dimensional crossover caused by the local inhomogeneity. The necessary condition for observation of inhomogeneity effects is also discussed.
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Yasuhiro Utsumi, Masahiko Hayashi, Hiromichi Ebisawa
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2739-2742
Published: 2000
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We investigate the dynamical quantum fluctuation effect on an Andreev current through an ultrasmall superconductor in the Coulomb blockade regime. We calculate the current using a phenomenological gauge invariant model and the real-time path-integral method. We choose a special gauge which absorbs the scalar potential to convert the phase of a superconductor as a dynamical variable. A zero-energy phase fluctuation of the superconductor suppresses the Andreev current at low bias voltage. This suppression is expected to be observed in samples with large level spacing and small charging energy which allow the coexistence of a large quantum fluctuation and Andreev reflection process.
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Iduru Shigeta, Toll Uchida, Yukihiro Tominari, Takeshi Arai, Fusao Ich ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2743-2746
Published: 2000
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We report the experimental results of quasiparticle tunneling using Bi
2Sr
2CaCu
2O
8+δ (BSCCO)-SiO-Ag planar junctions. For the {001}-oriented junctions, we have measured a well-known V-shaped gap structure expected for d-wave superconductors. For the {100}- and {110}-oriented junctions, a reproducible zero bias conductance peak (ZBCP) enhancement has been observed. The temperature dependence of the ZBCP is also presented. The ZBCP was observed below T
c. Our results are consistent with those of recent studies on the Andreev reflection between a d-wave superconductor and a normal metal.
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Satoshi Okuma, Masaki Arai
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2747-2750
Published: 2000
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We have performed four-terminal ac complex resistivity measurements in the linear regime, as well as dc resistivity measurements, for thick a-Mo
xSi
1-x films in constant magnetic fields (B = 0.1 and 1 T). The critical behavior associated with the second-order transition has been observed for both dc and ac resistivities. This is the first convincing evidence for the vortex-glass transition (VGT) in the homogeneously disordered low-T
C superconductors containing microscopic pinning centers. On the basis of this result, together with our previous finding of VGT in granular In films, we conclude that the VGT is universal in type-II superconductors with moderate disorder independent of whether pinning is microscopic or mesoscopic, or whether they are high-T
C or low-T
C superconductors.
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Yoshiyuki Fukumoto
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2755-2758
Published: 2000
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By using the perturbation expansion up to the fifth order, we study the two-triplet-dimer (TD) excitation spectra in the Shastry-Sutherland model, where the localized nature of a TD, the propagation of a TD pair by the correlated hopping and the long-range interactions between TD's play an essential role. It is found that the dispersion relations for first-neighbor TD pair excitations with S=1 and p-type symmetry qualitatively explain the second-lowest branch observed in the neutron inelastic scattering experiment. It is also predicted that the second-lowest branch consists of two components, p
x- and p
y-states, with slightly different excitation energies. The origin of the singlet mode at 3.7 meV observed in the Raman scattering experiment is also discussed.
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Tetsuo Ohama, Atsushi Goto, Tadashi Shimizu, Emi Ninomiya, Hiroshi Saw ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2751-2754
Published: 2000
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23Na NMR spectrum measurements in α
'-NaV
2O
5 with a single-crystalline sample are reported. In the charge-ordered phase, the number of inequivalent Na sites observed is more than that expected from the low-temperature structures of space group Fmm2 reported so far. This disagreement indicates that the real structure, including both atomic displacement and charge disproportionation, is of lower symmetry. It is suggested that zigzag ordering is the most probable. It is also found that the temperature variation of the NMR spectra near the transition temperature is incompatible with that of second-order transitions.
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Hiroshi Uozaki, Takahiko Sasaki, Satoshi Endo, Naoki Toyota
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2759-2762
Published: 2000
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To study the magnetic ground state in the title compound of a quasi two-dimensional charge transfer salt containing Fe
3+ (S = 5/2) paramagnetic ions, we have measured the magnetic torque at 0.4 K ≤ T ≤ 4 K and H ≤ 14 T using a capacitive cantilever torque meter. The torque and magnetization data above 1 K are well scaled by the Brillouin plot with a Weiss temperature of -0.8 K. From theoretical analysis for a uniaxial antiferromagnet, anomalous torque curves below 1 K reveal that an antiferromagnetic ordering with its easy axis perpendicular to the conducting ac-plane occurs between 0.5 K and 1 K. This antiferromagnetic order coexists with the metallic state of π-electrons, indicating quite weak π-d interaction.
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Hiroyuki Nakamura, Tomoaki Yamasaki, Saurav Giri, Hideto Imai, Masayuk ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2763-2766
Published: 2000
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We performed powder neutron diffraction and scattering experiments of the S = \frac{1}{2}$ triangular lattice system, BaVS
3, and found magnetic reflections below T
X \simeq 30$ K. The propagation vector is determined to be incommensurate (0.226 0.226 0) in the hexagonal index. The ordered moment is roughly estimated to be ∼ 0.5μ
B/V. Although the elastic magnetic diffractions disappear above T
X, low-energy inelastic scattering, which has an Q-ω dispersion similar to that below T
X, was observed between T
X and the metal-insulator transition point T
MI \simeq 70$ K, indicating the presence of a long-range and dynamic antiferromagnetic correlation, i.e., a spin-liquid-like state, between T
X and T
MI.
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Kaori Kuzushita, Shotaro Morimoto, Saburo Nasu, Shin Nakamura
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2767-2770
Published: 2000
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The charge disproportionation and the magnetic properties of Sr
3Fe
2O
7, which has a double-layered perovskite structure, have been investigated. From
57Fe Mössbauer measurements, the Néel temperature T
N and the critical temperature for the charge disproportionation reaction (2Fe
4+→Fe
3++Fe
5+) are determined to be 120 K± 2 K and 343 K± 10 K, respectively. Above 343 K, spectra clearly show a Fe
4+ singlet. The
57Fe Mössbauer spectrum at 4.5 K under externally applied longitudinal magnetic field consists of four magnetically split components and is similar to the spectrum obtained from CaFeO
3 with a helical spin structure. With an increase of the external magnetic field, the relative intensity of the 2nd and 5th absorption peaks increases, which implies that the magnetic moments of Fe have a tendency to form a texture perpendicular to the direction of the external magnetic field.
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Akira Sekiyama, Koji Kadono, Kyoko Matsuda, Takeshi Iwasaki, Shigenori ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2771-2774
Published: 2000
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``Bulk-sensitive'' Ce 3d-4f resonance photoemission (RPES) with an unprecedentedly high resolution has revealed a clear difference of bulk Ce 4f spectral weights of heavy fermion system CeRu
2Si
2 and CeRu
2Ge
2 in the region of the tail of the Kondo peak and its spin-orbit partner. The significant spectral difference in both materials is in strong contrast to the mutually similar ``surface-sensitive'' 4d-4f RPES. The obtained bulk-sensitive spectra are well reproduced by a single impurity model. Consideration of the crystalline electric field splitting is important for estimating a realistic Kondo temperature from the bulk 4f spectra.
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Fumitaka Sakamoto, Kenji Miyakawa
Article type: Cross-Disciplinary Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2775-2778
Published: 2000
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Dynamic behaviors of reduction waves are studied in a one-dimensional gel coupled with the Belousov-Zhabotinsky reaction as a function of temperature and composition of the reaction solution. The most striking behaviors observed are self-replication and preservation of reduction pulse waves. In the former dynamics, after the propagating reduction pulse wave vanishes, it splits into two counterpropagating pulses. In the latter dynamics, counterpropagating reduction pulse waves annihilate each other upon head-on collision and then reappear. Furthermore, annihilation and preservation of reduction waves are observed to occur simultaneously upon head-on collision.
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Takahiko Miyakawa, Kenji Oda, Toru Suzuki, Hiroyuki Yabu
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2779-2785
Published: 2000
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Static properties of a bose-fermi mixture of trapped potassium atoms are studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for both repulsive and attractive bose-fermi interatomic potentials. Qualitative estimates are given for solutions of the coupled equations, and the parameter regions are obtained analytically for the boson-density profile change and for the boson/fermion phase separation. Especially, a combination of the coupling constants and the particle numbers is found that discriminates the region of the large boson-profile change. These estimates are applied for numerical results for the potassium atoms and their consistency is verified.
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Mitsuyoshi Tomiya, Naotaka Yoshinaga
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2786-2791
Published: 2000
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The mode fluctuation distribution (MFD) of three-dimensional quartic oscillators coupled by quartic perturbations is numerically studied. The system is continuously transferred from the integrable to the chaotic regime by changing a single coupling strength. The MFD of the three-dimensional systems is found to be a sensitive measure of integrability as in two-dimensional systems. If the system is exactly integrable, the MFD has the characteristic skew distribution. On the other hand, even in the region that the chaotic and integrable volumes are comparable in the phase space, the MFD already becomes almost the Gaussian distribution as in the completely chaotic regime. We also find that the Brody parameter increases gradually without a plateau by increasing the coupling constant. It shows a clear contrast to the two-dimensional system.
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Keiji Saito, Taro Nagao
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2792-2797
Published: 2000
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The bootstrapped density of states introduced by Bogomolny and Keating for classically chaotic systems is applied to integrable systems, and the condition which leads to the universal nature of correlation between levels is investigated. We consider the two-point correlation function of the d-dimensional billiard system. We find the condition between the dimension and the periodic orbit sum in the semiclassical trace formula under which condition the correlation is well described by the Poisson statistics.
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Michinori Shiomi, Fumitaka Matsubara, Takayuki Shirakura
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2798-2807
Published: 2000
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We examine the phase transition of Ising spin glass models in two dimensions (2D), calculating complementary two quantities, i.e., the interface free energy $\overline{Δ F(T)} and the Binder parameter g
L, on finite L × L (L ≤ 24) lattices at very low temperatures T. We find that these quantities exhibit quite different features depending on the distribution of bonds. For the ± J distribution, $\overline{Δ F(T)} at very low temperatures slightly increases with L and g
L intersect at T ∼ 0.25J. These results suggest a non-zero temperature phase transition, T
c ≠ 0. On the other hand, for the Gaussian distribution, $\overline{Δ F(T)} decreases as L increases even at T = 0 and g
L for different L converges to unity at T = 0. These results confirm the assumption of the zero temperature phase transition, T
c = 0. Finite-size scaling analyses support those results. Thus we suggest that, in 2D, the existence of a finite-temperature phase transition depends on the distribution of bonds and it exists when the bond distribution is ± J.
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Keita Ogawa, Yukiyasu Ozeki
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2808-2815
Published: 2000
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The non-equilibrium relaxation method (NER) is applied to a frustrated spin system with competitive interactions. The critical point and critical exponents are estimated accurately for the Blume-Emery-Griffiths model in three dimensions. It is applied to the region where successive transitions of PM-FM-PM-SQ phases occur; we denote paramagnetic (PM), ferromagnetic (FM) and staggered quadrupole (SQ) phases. With the analysis for relaxation of fluctuations, we can estimate various critical exponents. The result indicates that all transitions belong to the Ising universality class in three dimensions. It is found that the NER method is useful to analyze the critical phenomena for complex systems in which equilibrium simulation is even difficult.
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Katsuki Katayama, Tsuyoshi Horiguchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2816-2824
Published: 2000
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We investigate a fully connected Hopfield neural network with spin-S (S ≥ 1) Ising neurons, including S=∞, when binary patterns are embedded by the Hebbian learning rule. We analyze the energy function of the neural network using the replica method. We investigate a generalization ability of the neural network within the replica symmetric (RS) solutions. We clarify that the generalization ability of the neural network with a larger value of S is enhanced when the finite number of concepts are extracted from the presented examples.
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Hidezumi Terazawa
Article type: Elementary Particles and Fields
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2825-2828
Published: 2000
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It is pointed out that the two abnormal cosmic ray events with the charge of Z=14 and the mass number of A \cong 370$ found in 1990 by Saito et al.1 can be explained by either one of the following three possibilities: 1) super-hypernuclei, 2) technibaryonic nuclei or technibaryon-nucleus atoms, and 3) ``color-balled nuclei''. How to distinguish among these three in future experiments is discussed in some detail.
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Chikako Uchiyama, Fumiaki Shibata
Article type: Atoms and Molecules
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2829-2844
Published: 2000
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The formation of the atomic coherence via a photon field has been considered to play an essential role in the laser action. The importance of the formation has been also recognized from the viewpoint of cavity QED. This paper analyzes quantum mechanical dynamics of a self-organized formation of coherence between atoms and photon field. We solved an equation of a reduced density operator for a quantum laser model with plural atoms by using coherent states and orthogonal polynomials, and obtained a solution in a continued fraction form. We numerically evaluate time evolution of averaged physical quantities and quasi-probability density of photon field. Under an appropriate condition for laser oscillation, time evolution of an average of induced atomic dipole moments shows a co-operative phenomenon. Numerical evaluation of the quasi-probability density of a photon field reveals that a coherently more stabilized and stronger photon field emerges as the number of atoms increases. To our knowledge, this is the first detailed quantum mechanical analysis on the self-organized formation of coherence within atoms beyond an intuitive explanation of a laser oscillation. Moreover, our formulation also provides a tool to analyze phenomena observed in microcavity QED experiments.
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Osamu Kujirai, Youichi Ogawa
Article type: Atoms and Molecules
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2845-2849
Published: 2000
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Autoionization states of neutral praseodymium atom (Pr I) were investigated using two-color two-step laser resonance ionization spectroscopy (RIS). A Pr hollow cathode lamp was used as an atomic source and optogalvanic signals were measured. The Pr I was excited from the ground state to four first step excitation levels (21120.69, 21471.81, 22014.11 and 23067.34 cm
-1) by the first step laser. These four channels were used to study odd-parity autoionization states. Four dyes were used in the second step excitation. The 108 odd-parity autoionization states were found by optogalvanic spectroscopy and their total angular momentum (J) values were estimated.
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Tetsuichiro Hayakawa, Kiyonobu Nagaya, Koichi Hamada, Yoshinori Ohmasa ...
Article type: Atoms and Molecules
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2850-2858
Published: 2000
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The photon energy dependence of the photoelectron photoion coincidence (PEPICO) spectra near the Se K-edge have been measured for Se
2 and larger species such as Se
5 at the BL-12C in Photon Factory. The PEPICO spectra reveal that the multiply charged ions, Se
z+, are produced as a result of the de-excitation process following the inner-shell excitation. Two prominent structures corresponding to the π
* and σ
* resonances are clearly observed in the energy dependence of the branching ratio from Se
2, while only one structure corresponding to the σ
* resonance can be seen for the larger species. At the σ
* resonance, the production of Se
+ and Se
2+ is enhanced, in comparison with the direct ionization where the core-hole states are completely relaxed before the dissociation. The energies of the π
* and σ
* resonance relative to the 1s ionization potential are estimated at -10.0± 0.5 eV and -5± 1 eV, respectively. In addition, we propose a new method for the size-selective structural analysis of clusters by utilizing the PEPICO measurements.
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Sang June Hahn, Su–Bin Song
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2859-2865
Published: 2000
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We have investigated the stable operation regime of the short-pulse FEL oscillator system. Two different stable-focus regimes of stable operation have been identified. The one is a single-mode stable regime (SSR) and the other is a bump stable regime (BSR). The former is operated with a large cavity detuning and gives a single-mode stationary state without saturation. And the latter is operated near perfect cavity synchronism with a low current and gives a multi-mode stationary state after a transient bump of the macropulse power. Using properly defined collective phase variables, we describe the electron dynamics and the phase evolution of the optical field in the stable operation regimes.
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Hiroaki Ono
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2866-2872
Published: 2000
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By the reductive perturbation method, Faraday rotation of electromagnetic waves propagating in a nonlinear dielectric medium parallel to an external magnetic field is investigated. The derived equation takes the form of derivative nonlinear Schrödinger (DNLS) equation appropriate to boundary value problems. Based upon this equation, we have considered how the linear Faraday effect is modified. It is found that a linearly polarized wave incident to the dielectric medium under an external magnetic field shows the Faraday rotation whose angle is the same as that for linear waves in the lowest order but slightly modified by the third harmonic waves generated by the mutual interaction of the right and left polarized waves. On the other hand, an elliptically polarized wave shows the nonlinear Faraday rotation whose angle is dependent on the square of the amplitude of an incident wave. Further the inverse Faraday effect is estimated to be proportional to the square of the magnitude of an incident nonlinear circularly polarized wave train. In addition to the present dielectric medium, these phenomena are expected to occur in many systems subject to DNLS equations such as a ferromagnet.
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Xun–Li Feng, Jing–Tao Zhang, Zhi–Zhan Xu
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2873-2877
Published: 2000
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The photon statistics of the two-photon fluorescence of a two-level atom in a squeezed vacuum is investigated by using the second-order correlation function g
(2)(t). Based on its analytical solution, g
(2)(t) is found to be an oscillatory function of time when the average photon number of the squeezed vacuum light field is above a threshold. The origin of the oscillatory behavior of g
(2)(t), which generally results from the external driving field for resonance fluorescence, is the driving effect of the squeezed vacuum light field on the atom. It is also found that the oscillatory behavior of g
(2)(t) can provide a measurement of the ac Stark effect.
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Christine Fernandes Xavier, Roberto Antonio Antonio
Article type: Classical Phenomenology and Applications
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2878-2882
Published: 2000
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An hydrodynamic model for sonoluminescence in diatomic gases, taking into account vibrational relaxation effects is presented. Allowing for heat conduction at the bubble boundary and using the Gilmore approximation for the bubble radius equation, it is possible to obtain different maximum gas temperatures associated to translational/rotational degrees of freedom and to vibrational ones. The difference in maximum temperatures should be negligible in the case of oxygen but it should reach large values in the case of nitrogen. This indicates that care should be taken when amounts of dissociation and/or amounts of ionization are estimated in sonoluminescence, starting from the thermodynamic equilibrium hypotheses. It may happen that the velocity of the bubble collapse is so high that such kinds of processes have no sufficient time to develop.
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Tomejiro Yamagishi, Makoto Tsukayama
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2883-2888
Published: 2000
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Dynamics of externally driven ion sheath in the double plasma device has been investigated by numerically solving a nonlinear differential equation. The global dynamical changes of the system have been examined by evaluating parametric changes of the Poincaré map and the maximum Lyapunov exponent. The transitions to chaos caused by the cascade bifurcation and intermittency are clearly shown by graphical methods. The correlation dimension calculated for a strange attractor, D
2∼ 1.54, agrees well with the experimental one indicates that the chaos is low dimensional, and the system can be described by the low dimensional equation.
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Tomejiro Yamagishi
Article type: Fluids, Plasmas, and Electric Discharges
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2889-2894
Published: 2000
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The discontinuity at the boundary between an area preserving system and dissipative system has been studied by investigating the effect of weak dissipation on drift orbits making use of a simple mapping model in a helical magnetic field. It is found that, after many mapping iterations, any orbit even chaotic one tends to an attractor forming a vortex line with a very small dissipation. The number of iteration to converge within a certain distance from the attractor is inversely proportional to the amount of the dissipation. Although the behavior of orbits completely change, the basic stability characteristics of the system does not change, i.e., the coordinate of the attractors are determined by the stable fixed points in the area preserving system. Since wide range of orbits are concentrated around the attractors after many toroidal rotations, a pinch effect is created by a small dissipation. Application of this pinch effect to fusion plasmas is discussed.
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Takanao Asahi, Katsuhiko Hasebe, Akira Onodera
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2895-2899
Published: 2000
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Crystal structure of the high pressure phase VI of thiourea, SC(NH
2)
2, has been analyzed at 0.97 GPa, 295 K from X-ray diffraction data; orthorhombic, Pbnm, a=5.503 Å, b=7.138 Å, c=24.788 Å, Z=12, R=0.055 for 351 independent reflections. Displacements of molecules at V-VI phase transition bring about reconstruction of hydrogen bonds network.
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Sheng–You Huang, Xian–Wu Zou, Wen–Bing Zhang, Zhun&n ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2900-2904
Published: 2000
Released on J-STAGE: November 30, 2000
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Molecular dynamics simulations have been carried out to investigate the energy localization in a one-dimensional Morse lattice with an impurity. The energy distribution around the impurity site is studied. It shows that the potential energy localization is only limited to the impurity and its nearest neighboring particles. Influence of the repulsive and attractive parts of the potential on the energy localization around an impurity has also been studied. The results show that at intermediate and high temperatures the repulsive potential dominates the quantitative behavior of the energy localization of the impurity. The attractions are manifested primarily in the low temperature range, but this effect decreases as the temperature increases and is almost negligible at high temperatures. They also show that in thermal equilibrium, the average potential energy of the impurity increases with decreasing repulsion stiffness, and decreases with reduced attraction one. The results are explained by the soliton fusion theory of a Toda lattice.
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Hirotake Shigematsu, Hiroyuki Mashiyama, Masaki Takesada, Ken–ic ...
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2905-2909
Published: 2000
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The soft phonon modes, which are related to the normal-incommensurate phase transition of Rb
2ZnBr
4, have been measured by inelastic neutron scattering. The existence of both phase and amplitude modes has been confirmed, and the phonon dispersion curves have been determined in the low-temperature commensurate phase. On the other hand, the phonon dispersion curve of the transverse acoustic phonon along the (0 0 ξ) direction does not vary appreciably in the normal phase. The soft mode is fully overdamped above the normal-incommensurate phase transition. Diffuse scattering develops around h0l±5/17 as temperature approaches T
i =347 K from above.
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Toshikuni Miyazaki, Mamoru Yamashita
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2910-2916
Published: 2000
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The surface stabilized smectic A phase of homeotropic alignment (SmAII) appears even under the homogeneous anchoring due to an effect of walls as the symmetry breaking field to the smectic layer. As an analogue of the Freedericksz transition at nematic phase, a response of the transverse electric field at SmAII is studied by the constant temperature molecular dynamics simulation of the Gay-Berne system sandwiched by the walls, where each molecule has an electric dipole along the molecular long axis. At a threshold of the field strength, the system changes to the smectic A phase with layer normal being parallel to the electric field (SmAI) via an intermediate phase like a smectic C phase. By reducing the field, again SmAII appears directly, showing a hysteresis characteristic to the discontinuous transition. The dipole-dipole interaction is proved to stabilize the layer structure of smectics, while SmAI changes to smectic C phase in the electric field.
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Jun Takeda, Toshiyuki Inukai, Masatoshi Sato
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2917-2922
Published: 2000
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Behavior of the electronic specific heat C
el of La
2-x-zNd
zSr
xCu
1-yZn
yO
4 has been investigated over the wide temperature (T) range between 2 K and 300 K. For samples with z=0.4 and 0.0≤q x≤q 0.25, by carefully subtracting the phonon contribution from the total specific heat, the electronic specific heat coefficient γ≡ C
el/T has been extracted, where anomalous x- and T-dependence related to the so-called 1/8 problem or the ``stripe'' order is observed. Zn-doping effects on the behavior of γ(T) of La
2-xSr
xCu
1-yZn
yO
4 (x=0.10 and 0.08) and La
1.88-zNd
zSr
0.12Cu
1-yZn
yO
4 (z=0.2 and 0.4) suggest that not only the long range ``stripe'' order but also the fluctuating ``stripe'' suppress both the pseudo gap and the singlet pair formation.
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Wen Sheng Lai, Qing Zhang, Bai Xin Liu, Bai Xin Ma
Article type: Condensed Matter: Structure, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2923-2937
Published: 2000
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An n-body Ni–Ti potential is derived and verified to be capable of reproducing some physical properties in the Ni–Ti system. Applying the constructed potential molecular dynamics simulations of solid-state reaction in the Ni–Ti multilayers reveal that the growth of an amorphous interlayer follows a linear t correlation at the very beginning and then shifts to exactly a t
1/2 law and that a sharp semi-coherent interface serves as a nucleation barrier, preventing the interfacial reaction at a temperature up to 873 K. Moreover, the asymmetric growth of amorphous interlayer is found to originate from the sequential disordering of constituent metals by dissolving its partner atoms beyond its maximum allowable solubility, which is named as a solubility criterion. In addition, the calculated maximum solid solubilities also predict that an intrinsic glass forming range in the Ni–Ti system is from 15 to 62\,at.\0f Ni, which is in good agreement with the experimental results.
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Hitoshi Sugawara, Yukihiro Abe, Yuji Aoki, Hideyuki Sato, Masato Hedo, ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2938-2946
Published: 2000
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We have investigated the de Haas-van Alphen (dHvA) effect and the transverse magnetoresistance in filled skutterudite LaFe
4P
12 and NdFe
4P
12. The Fermi surface of LaFe
4P
12 consists of a nearly spherical hole sheet and a multiply connected one. These features are explained reasonably well by a full potential linearized augmented-plane-wave (FLAPW) band structure calculation. The Fermi surface of NdFe
4P
12 is similar to those in LaFe
4P
12 except the exchange splitting in the dHvA frequencies. The cyclotron effective masses are enhanced roughly twice compared to those of LaFe
4P
12 due to the electron-magnon interaction.
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Shinji Watanabe
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2947-2952
Published: 2000
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The magnetization process in the one-dimensional Kondo lattice model away from half filling (n
c<1) is studied on the basis of the density matrix renormalization group method. A rapid increase of the magnetization is caused by the collapse of the intersite incommensurate correlation of f spins. On the contrary, the intrasite f-c singlet correlation survives in the larger magnetic field. The crossover from large to small Fermi surfaces for majority and minority spins is observed, whereas the Fermi surfaces are always contributed by f spins. A magnetization plateau appears with the magnitude of 1-n
c. The lower end and the upper end of the plateau are related to the coherence temperature and the Kondo temperature, respectively, which play the essential role in heavy electron systems as the characteristic energies.
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Masanori Yumoto, Hidetoshi Fukuyama, Hiroshi Matsukawa, Naoto Nagaosa
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2953-2961
Published: 2000
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We investigate quantum depinning of the one-dimensional (1D) commensurate charge-density wave (CDW) in the presence of one impurity theoretically. Quantum tunneling rate below but close to the threshold field is calculated at absolute zero temperature by use of the phase Hamiltonian within the WKB approximation. We show that the impurity can induce localized fluctuation and enhance the quantum depinning. The electric field dependence of the tunneling rate in the presence of the impurity is different from that in its absence.
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Naoki Watanabe, Masaru Tsukada
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2962-2968
Published: 2000
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A fast and stable numerical method is formulated to compute the time evolution of a wave function in a magnetic field by solving the time-dependent Schrödinger equation. This computational method is based on the finite element method in real space to improved accuracy without any increase of computational cost. This method is also based on Suzuki's exponential product theory to afford an efficient way to manage the TD-Schr{ö}dinger equation with a vector potential. Applying this method to some simple electron dynamics, we have confirmed its efficiency and accuracy.
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Gen Tatara
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2969-2972
Published: 2000
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The scattering of the electron by a domain wall in a nano-wire is calculated perturbatively to the lowest order. The resistance is calculated by use of Landauer's formula. The result is shown to agree with the result of the linear response theory if the equilibrium is assumed in the four-terminal case.
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Chih–Kai Yang
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2973-2976
Published: 2000
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Our first principles calculation has shown that single 3d transition-metal atoms embedded in the surface layer of Cu(001) can have considerable magnetic moments. In addition, the Cu atoms closest to the impurity in the same layer also possess appreciable moment, which is not realized if the impurity is embedded in bulk Cu. The calculation indicates that intense d-d interaction and heavy charge exchange between the impurity and the host atoms occur in the surface layer, which therefore facilitates the enhancement of magnetism.
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Yoji Ohashi
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2977-2992
Published: 2000
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We theoretically investigate antiferromagnetic (AF) spin fluctuations in impurity-doped high-T
c superconductivity. We assume a d
x2-y2-wave superconductor with strong AF spin fluctuations, and take into account nonmagnetic impurities within the t-matrix approximation. In the clean system, the imaginary part of the AF spin susceptibility (Imχ(Q,ω)) is suppressed far below the excitation gap E
g=2×Max[Δ
p] (Δ
p: superconducting order parameter), while it has a peak slightly below E
g. On the other hand, in the presence of unitarity scatterers, it is shown that Imχ(Q,ω) far below E
g increases with decreasing temperature even in the superconducting state. As a result, at low temperatures, Imχ(Q,ω) has two peaks far and slightly below E
g as observed in Zn-doped YBa
2Cu
3O
6.97. In addition, because of the enhancement of the low-energy AF spin fluctuations, the nuclear spin-lattice relaxation rate on Cu ((1/T
1T)
Cu) also increases at low temperatures in contrast to the case of the clean superconductivity. This result can explain the recent experiment on (1/T
1T)
Cu in Zn-doped YBa
2Cu
4O
8.
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Ryusuke Ikeda, Hiroto Adachi
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
2993-3006
Published: 2000
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A vortex-glass transition due to point disorder in layered superconductors is studied for the case with an applied field parallel to the layers. Our calculation of tilt responses indicates that, irrespective of the magnitude of the field, the resulting glass phase, Josephson-vortex-glass (JG), should have a transverse Meissner effect, as in a planar splayed glass phase, only for a tilt perpendicular to the layers. Further, focusing on the high field (and/or high anisotropy) region $B \sqrt{{\mitΓ}} > φ
0/d
2, where Γ is the mass anisotropy in the Lawrence-Doniach model, the JG transition line T
JG(B) is shown to have a similar form to a B-T line following from the disorder-free Lindemann criterion and to decrease with increasing $B \sqrt{{\mitΓ}}, in marked contrast to the disorder-free melting line insensitive to $B \sqrt{{\mitΓ}} in such the high field region. This T
JG(B) line seems to have been recently observed in a.c. susceptibility and in-plane resistivity measurements in BSCCO and qualitatively explains a field dependence at lower temperatures of previous BSCCO resistivity data showing the so-called in-plane Lorentz force-free behavior.
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Yasusi Koyama, Yositake Takane, Hiromichi Ebisawa
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
3007-3016
Published: 2000
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We obtain an analytical expression for the conductance fluctuation in a superconductor-dirty normal conductor-superconductor (SNS) junction using the Green's function method. It is shown that the magnitude of the fluctuation is enhanced by a factor of (L
φ/L
x)
(4-d)/2 compared with the universal value of the order of e
2/\hbar (L
φ: the phase coherence length, L
x: the separation between two superconductors, d: the effective dimension of the normal region). It is also shown that the energy correlation range is of the order of the inverse of the phase relaxation time, in contrast to ordinary cases where the energy correlation range is of the order of the Thouless energy. We calculate the phase coherence length L
φ as a function of the sample size and find that L
φ becomes longer with the reduction of the sample size. This indicates that the conductance fluctuation in an SNS junction can be strongly enhanced beyond the universal value.
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Yasunobu Fujimori, Shin–ichi Kan, Bunjyu Shinozaki, Takasi Kawag ...
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
3017-3026
Published: 2000
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The electrical resistivity, heat capacity, superconducting upper
critical magnetic field and magnetic susceptibility of NiBi
3 have been measured for the polycrystal and needle crystal. The temperature dependence of
the resistivity ρ(T) above the superconducting transition temperature can be explained by the parallel resistor formula. From ρ(T), using the sum of two Gruneisen-Bloch functions, we have obtained that the lower main value
of the Debye temperature is 70 K and the higher one is 300 K. This is compatible with ω
E≡ 30.6 K and ω
D≡ 141 K
obtained from the heat capacity using the hybrid Einstein-Debye model. We have compared the angular dependence of the critical magnetic field with that of the effective mass model and found an anisotropic mass ratio $m_{\parallel b}/m_{\perp b}\approx 0.17$ for the needle (//b-axis) crystal. Almost
the same value of 0.14 is also obtained from the analysis of ρ(T).
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Atsuko Fukaya, Atsuko Ito, Hiroko Aruga Katori, Tsuneaki Goto
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
3027-3039
Published: 2000
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The diluted antiferromagnet Mn
xMg
1-xTiO
3 with x ≥ 0.64 has been studied by magnetization measurements, and the magnetic phase diagrams in the field-temperature (H-T) plane have been determined for the samples with different x including pure MnTiO
3. It is demonstrated that the existence of random fields gives large effects on the phase transitions. The most noticeable result is that the H-T phase diagram of the samples except MnTiO
3 consists of four phases: well known three phases of a paramagnetic, an antiferromagnetic (AF) and a spin-flop (SF) phase, and a new type of phase. The shape of the phase diagram changes systematically as the Mn concentration, x, decreases. It is considered that in this ``new phase'' an AF like short range order and a SF like short range order coexist and that appearance of the ``new phase'' is caused by random fields. In this paper, we discuss the effects of random fields on the phase diagram of Mn
xMg
1-xTiO
3 and the x dependence of phase diagram.
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Seong–Jae Lee, Wathiq Abdul–Razzaq
Article type: Condensed Matter: Electronic Properties, etc.
Subject area: Mathematical methods in physics.
2000 Volume 69 Issue 9 Pages
3040-3044
Published: 2000
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In this study, the transition temperatures T
p due to the interlayer-coupling in Fe/Al and in Ni/Cu multilayered films made by sputtering technique, are compared with the Curie temperatures. These T
p temperatures are believed to be caused by bi-linear antiferromagnetic couplings between the magnetic films (Fe, Ni) via the non-magnetic films (Al, Cu). A comparison is also made with a recent study on Fe/Al made by the MBE technique in which the transition temperature is caused by a bi-quadratic coupling.
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