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Hironori Nakao, Ko-ichi Magishi, Yusuke Wakabayashi, Youichi Murakami, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1857-1860
Published: 2001
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Under zero magnetic field, a quadrupolar order parameter at q
Q=(1/2,1/2,1/2) in a typical antiferro-quadrupole (AFQ) ordering compound CeB
6 has been observed for the first time by means of a resonant X-ray scattering (RXS) technique. The RXS is observed at the 2p → 5d dipole transition energy of the Ce L
3-edge. Using this RXS technique to observe the pure order parameter of the AFQ state, the magnetic phase diagram of Phase II is first determined.
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Kazuaki Kobayashi, Kazuo Yamamoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1861-1864
Published: 2001
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Electronic and lattice properties of MgB
2 under uniaxial and hydrostatic compression are calculated. Lattice properties are optimized automatically by using the first-principles molecular dynamics (FPMD) method. Features of the electronic band structures under uniaxial and hydrostatic compression are quite different from each other.
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Eiji Hatta, Tadashi Sasaki, Vladimir M. Svistunov, Mikhail A. Belogolo ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1865-1868
Published: 2001
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Tunneling spectroscopy measurements on normal state Gd-Gd oxide-Al junctions have been performed. Small deviations from the overall parabolic dependence of conductance on voltage were revealed and analyzed using a theoretical approach, taking into account interactions of tunneling electrons with elementary excitations in the oxide layer and metal electrodes. These processes have been studied by calculating the even and odd conductances that characterize the symmetrical (emission of oxide phonons) and asymmetrical (self-energy effects in electrodes) processes, respectively. It has been found that in gadolinium, one of the simplest magnetic metals known, an interaction of electrons with magnetic excitations is as important as the electron-phonon contribution. This result explains the difference between the calculated electron-phonon coupling parameters and the experimentally derived electron mass enhancement factors in magnetic rare-earth metals.
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Yositake Takane, Katsunori Wakabayashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1869-1872
Published: 2001
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Collective electron transport in mesoscopic charge-density-wave (CDW) systems is studied theoretically. Sliding motion of the CDW is accompanied by thermally activated phase-slip processes near electrical contacts. Each phase-slip event gives rise to an addition or removal of a wavefront, resulting in deformation of the overall phase profile. Since the energy barrier for thermal nucleation of phase-slip centers strongly depends on the phase profile, its deformation affects the phase-slip rate, particularly in small samples. We calculate the nonlinear behavior between the CDW current and the phase-slip voltage V
ps, taking account of the small-size effect on the phase-slip rate. Using the parameters for NbSe
3, we find that the small-size effect reduces V
ps when the sample length is smaller than a few micrometers. This behavior is consistent with the recent experiment by Mantel
et al.: Phys. Rev. Lett.
84 (2000) 538 for mesoscopic NbSe
3 wires.
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Hiroshi Kontani
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1873-1876
Published: 2001
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In high-T
c cuprates, the orbital magnetoresistance in plane (Δρ/ρ) is anomalously enhanced at lower tempemeratures compared with conventional Fermi liquids, and thus Kohler's rule is strongly violated. Moreover, it should be noted that an intimate relation between Δρ/ρ and the Hall coefficient (R
H), Δρ/ρ ∝ (R
H/ρ)
2, holds well experimentally, and is called the “modified Kohler's rule”. In this letter, we study this long-standing problem in terms of the nearly antiferromagnetic (AF) Fermi liquid. We analyze the exact expression for Δρ/ρ by including the vertex corrections (VC's) to keep the conservation laws, and find the approximate relation Δρ/ρ ∝ ξ
AF4 ρ
-2 · H
2 (ξ
AF being the AF correlation length) in the presence of AF fluctuations. The factor ξ
AF4, which comes from the VC's for the current, gives the additional temperature dependence. By taking account of the relation R
H ∝ ξ
AF2 [Kontani
et al.: Phys. Rev. B
59 (1999) 14723], we can naturally explain the modified Kohler's rule. In conclusion, based on the Fermi liquid theory, the famous seemingly non-Fermi liquid behaviors of R
H and Δρ/ρ in high-T
c cuprates are naturally understood on an equal footing.
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Makoto Maki, Terukazu Nishizaki, Kenji Shibata, Norio Kobayashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1877-1880
Published: 2001
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Low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) measurements have been performed on YBa
2Cu
3O
7-δ single crystals cleaved below 20 K in order to obtain clean surfaces. The observed STM images are classified into two types of atomic images corresponding to BaO and CuO-chain layers, and the superconducting STS spectra are observed only on the latter layer. In the BaO layer, barium atomic images are clearly observed for the first time in addition to oxygen atomic images. In the CuO-chain layer, on the other hand, we observe the oxygen atomic images, in which a number of oxygen vacancies form clusters along the b-axis. Moreover, the CuO-chain layer shows elliptically modulated electronic images which are attributed to the charge density wave in the CuO chains.
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Yutaka Itoh, Takato Machi, Nobuaki Watanabe, Seiji Adachi, Naoki Koshi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1881-1884
Published: 2001
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We studied low-frequency spin dynamics near the impurity-induced superconductor-to-insulator transition for underdoped high-T
c superconductor YBa
2(Cu
1-xM
x)
4O
8 (M=Ni, Zn) using the Cu nuclear quadrupole resonance (NQR) spin-echo technique. We observed remarkable suppression of the normal-state pseudo spin-gap and a loss of Cu NQR spectrum intensity at low temperatures around the critical impurity concentration.
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Takashi Hirai, Nobukatsu Yoshida, Yukio Tanaka, Jun-ichiro Inoue, Sato ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1885-1888
Published: 2001
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A method for identifying the parity of unconventional superconductors based on tunneling spectroscopy is proposed. For a model of calculation, we adopt a ferromagnet/superconductor (F/S) junction, the tunneling current of which is spin polarized. The tunneling conductance spectra are shown to be quite sensitive to the direction of the magnetization axis in the ferromagnet only when the superconductor has odd parity. Therefore, it is possible to distinguish the parity of the superconductor by performing tunneling spectroscopy in F/S junctions.
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Sheng Xu, Yutaka Moritomo, Kenichi Kato, Arao Nakamura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1889-1891
Published: 2001
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Effects of magnetic impurity on the superconductivity have been investigated in Mg
1-xMn
xB
2. With increase of Mn concentration x, the lattice constant c (perpendicular to the boron sheet) decreases at a rate of -1.4 % (= d\ln c/dx), while a remains nearly unchanged. The transition temperature T
c steeply decreases with x at a rate of dT
c/dx = - 159 K. These results suggest that superconducting state of the parent MgB
2 is amenable to the magnetic impurities, i.e., Mn
2+.
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Tohru Kawamoto, Madoka Tokumoto, Hirokazu Sakamoto, Kenji Mizoguchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1892-1895
Published: 2001
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We have theoretically studied pressure effects on molecular ferromagnet C
60 complexes with tetrakis (dimethylamino) ethylene (TDAE), particularly the pressure-induced depression of the Curie temperature. The observed behavior is well simulated by our model which is based on a charge transfer induced intramolecular Jahn-Teller distortion and an intermolecular cooperative Jahn-Teller interaction. We emphasize that the theoretical simulation is carried out with reasonable parameters known for C
60- complexes. It is concluded that the enhancement of the crystal field at C
60 sites due to increasing pressure causes the depression of Curie temperature.
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Koshi Takenaka, Yuko Sawaki, Shunji Sugai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1896-1899
Published: 2001
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Al-substituted La
0.825Sr
0.175MnO
3 shows a resistance minimum at low temperature. However, this cannot be explained within a simple localization picture because the optical conductivity is characterized not only by a non-Drude infrared peak but also by an additional absorption at about 3 eV. A small amount (∼3%) of vacancy (Al impurity) in the ferromagnetic Kondo lattice changes the overall character of the charge dynamics and induces the unconventional localization state.
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Katsurou Hanzawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1900-1903
Published: 2001
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Structure factors for magnetic scattering of neutrons by CeB
6 are calculated for the magnetic moment distributions at 1.5 K and 8 T (in phase II) determined from the analysis of the hyperfine field at B nuclei. 4f electrons of Ce are polarized magnetically with the magnetic moment of about 1μ
B per Ce parallel to the applied field, whereas 2p electrons of B are also polarized inversely by about -0.1μ
B per B
6 molecule. The structure factor S(Q) has a large anisotropy for the direction of the scattering vector Q due to the anisotropy of the 4f wave function. For small Q, an oscillatory feature appears in S(Q) due to the inhomogeneous spin densities on the 2p states of B sites. Diffraction peaks with half-integer indexes are predicted to appear in the large Q region, which will provide direct evidence of the antiferro-octupolar ordering induced by a magnetic field in phase II.
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Itaru Hataue
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1905-1911
Published: 2001
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In the present paper, the structure of the asymptotic numerical solutions which were calculated by using implicit schemes were studied. Analytical discussions and numerical tests for fully implicit schemes of the Burgers' equation and several types of their linearized schemes were done. Furthermore, we tried to investigate the characteristics of ghost numerical solutions of incompressible fluid equations from viewpoints of the effect of popular fourth order artificial viscosity terms. The calculation model adopted in the present paper was the flow around a circular cylinder and the Reynolds number was 2000. The non-dimensional incompressible Navier-Stokes equations and the continuity equation were solved numerically by using the MAC (Maker-And-Cell) method and an implicit scheme. Unsteady dynamical structure was investigated in detail by analyzing calculated time series data of drag coefficients.
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Kai-Seng Chou, Changzheng Qu
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1912-1916
Published: 2001
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It is shown that the KdV, Harry Dym, Sawada-Kotera hierarchies and the Kaup-Kupershmidt equation naturally arise from the motions of plane curves in special linear geometry SL(2). Motions of the curves corresponding to traveling waves as well as one- and two-solitons are investigated.
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Mikiso Mizuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1917-1923
Published: 2001
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Bell introduced the well known locality assumption, stating that the detector outcome of particle-1 could not influence the outcome of particle-2, and vice versa, when a singlet pair of particles was subjected to simultaneous experimental tests. Simple cases of violation of the inequalities were taken as proof of inapplicability of the given assumption of locality or hidden variables concept. To this date no one examined Bell's type inequalities for logical consistency from rigorous mathematical point of view. All the terms appearing in the inequalities deal with conditional probabilities given the detector orientations fixed. In brief, conditional probabilities and conditional expectations can be added, subtracted, or compared only when they are defined on the same conditional subensembles. Careful analyses of this paper show that this requirement is not met.
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Miki Wadati, Go Kato
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1924-1930
Published: 2001
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Statistical mechanics of a one-dimensional system of bosons with repulsive delta-function interaction is studied. Explicit calculations of the partition function and the cluster integrals are carried out. The results coincide with those by the thermal Bethe ansatz (TBA) method. Thermodynamic quantities such as the pressure, the chemical potential and the energy are given both for large and small coupling limits.
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Shokichi Kanno
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1931-1936
Published: 2001
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For a dilute gas interacting through a short range potential, we have obtained, by starting from the quantum mechanical Hamiltonian, a closed set of evolution equations for the particle distribution and for the expectation values of the four-field-operator products. The set of equations is invariant under time reversal. The evolution equation for the particle distribution depends on the initial conditions, and reduces to the Boltzmann transport equation for almost all initial states.
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Ae Ran Lim, Dae Keun Park, Jin-Hae Chang, Se-Young Jeong
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1937-1941
Published: 2001
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We studied the temperature dependence of the stress-strain hysteresis in [N(CH
3)
4]
2CuCl
4 and [N(CH
3)
4]
2ZnCl
4 single crystals grown by the slow evaporation method. From the obtained results, we determined that [N(CH
3)
4]
2CuCl
4 and [N(CH
3)
4]
2ZnCl
4 single crystals have ferroelastic characteristics in phase IV and III, and phase V and IV, respectively. Also, the ferroelastic domain switching stress due to saturation effect is approximately 0.9 MPa in [N(CH
3)
4]
2CuCl
4 and 0.4 MPa in [N(CH
3)
4]
2ZnCl
4 crystals. In order words, the ferroelastic phase transition due to external mechanical stress applied to these crystals causes a transformation from the twin-domain state to the single-domain state.
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Takeshi Miyazaki, Yu Furuichi, Naoya Takahashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1942-1953
Published: 2001
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An ellipsoidal vortex model is developed in order to investigate the dynamics of vortex interactions in a quasigeostrophic turbulence. Each coherent vortex is modeled by an ellipsoid of uniform potential vorticity. It is assumed that each vortex remains to be an ellipsoid, although its principal axes and inclination angles change under the influence of the strain field induced by other vortices. The dynamics of ellipsoidal vortices are shown to be a Hamiltonian system of finite degree of freedom extracted from the partial differential equations that describe quasigeostrophic vortex dynamics. The center of vorticity and the angular momentum are conserved, besides the total energy and Casimirs of the system, such as the vortex height and the vortex volume. Chaotic motions are observed even in a two-body system.
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Kim Hyeon-Deuk, Hisao Hayakawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1954-1965
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The inelastic Lorentz gas in cooling states is studied. It is found that the inelastic Lorentz gas is localized and that the mean square displacement of the inelastic Lorentz gas obeys a power of a logarithmic function of time. It is also found that the scaled position distribution of the inelastic Lorentz gas has an exponential tail, while the distribution is close to the Gaussian near the peak. Using a random walk model, we derive an analytical expression of the mean square displacement as a function of time and the restitution coefficient, which well agrees with the data of our simulation. The exponential tail of the scaled position distribution function is also obtained by the method of steepest descent.
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Abhimanyu Mishra, C. U. S. Patnaik, P. Misra
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1966-1970
Published: 2001
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Numerous workers have studied rf resonance probe under the condition ν
m« ω
ep, i.e. under collisionless condition, where ν
m is angular collision frequency and ω
ep is angular plasma frequency. In the present paper, the interaction of rf signal with a back diffusion type plasma has been studied without neglecting collision frequency. The problem has been discussed theoretically under this condition, and the derivation yields two expressions for which impedance is minimum. To verify the result experimentally, a rectangular plasma chamber is designed and fabricated, where electron density can be changed without changing the discharging potential and vacuum conditions. From the experiment two resonance peaks are obtained in the I-f
2 curve (I: current and f: applied frequency) corresponding to the two minimum impedance conditions, from which plasma parameters like electron density, collision frequency and electron temperature have been estimated.
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Shonosuke Ohta
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1971-1978
Published: 2001
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Two-dimensional off-lattice diffusion-limited clusters simulated in circular boundary of finite size are studied by comparison with analytical solution in annular Laplace field and trajectory density of Brownian particles. Radial growth rate in annular field classifies into two different areas. The one is cluster size dominated area, and the other is the area dominated by distance from the boundary. Results clarify that the ordinary diffusion-limited aggregation (DLA) grows under the condition of size dominated area. Radial density, fractal dimension, and branching structure of cluster growing in the circular boundary of finite size support a crossover at ∼ 0.37 that agrees with the analytical suggestion of 1/e=0.368 for the ratio of cluster size to boundary radius. Fractal to non-fractal change on self-similarity and change from tip splitting to side branching on micro branching structure characterize the morphological crossover of diffusion-limited cluster.
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Ezat Keshavarzi, Gholamabbas Parsafar
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1979-1985
Published: 2001
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The contributions of all non-ideally effects which arise from excluded volume, attractive and repulsive forces have been separated and investigated in the direct correlation function, DCF, using the Linear Isotherm Regularity, LIR for dense fluids. In such away we have shown that the core of the DCF (0<r<σ ) is related to the geometric effect which arises from the excluded volume, while the intermolecular interactions have an important role in the tail (σ <r<∞ ). Also mathematical expressions for the core and tail of the DCF have been presented via the bulk modulus and the LIR. These new expressions beside of satisfying the experimental DCF can also generate the structural factor of fluids. The other issue that we discuss in this article and should be noticed separately, is the effective pair potential. The effective pair potential is the intermolecular pair interactions in presence of the other molecules of the system. We have shown that the well depth of such an effective pair potential is shallower than that of the isolated pair which is in accordance with the reported results in the literatures. Our results suggest that the net effect of the medium on interactions between two molecules is positive (repulsion).
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Yuichi Michiue, Mamoru Watanabe
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1986-1989
Published: 2001
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The effects of K ion concentration on ionic correlations and dynamics of a hollandite-like one-dimensional ionic conductor have been studied by the molecular dynamics method. In the K concentration range 0.6 ≤ n ≤ 0.8, three peaks appeared in static structure factors and shifted with the variation of n. Peak positions were characterized by the two basis vectors, periods of unit separation of K ions (nc
*) and the host framework (c
*), which leads to an interpretation that K ions arranged with the unit separation, c/n, are perturbed by the framework potential with the period c. The low frequency mode (
ca. 15 cm
-1) was seen in dielectric function for 0.6 ≤ n ≤ 0.9, which is concerned with a K ion having one of the adjacent sites occupied and the other vacant. Another mode seen around 65 cm
-1 for n=0.7 and below is attributed to a local motion of a K ion whose adjacent cavities are both vacant.
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Hisashi Okumura, Fumiko Yonezawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1990-1994
Published: 2001
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We find out that the NVT plus test particle method is effective to obtain the reliable data for liquid-vapor critical point from microscopic information of interatomic potentials. The basic idea of this method is to calculate chemical potentials by test-particle insertions during canonical simulations, from which the equilibrium vapor pressure is determined. Simulations are performed at a fixed volume so that the undesirable volume fluctuations do not occur between the liquid and vapor phase. As a consequence it becomes possible to make the simulations stable even near the critical point. This is an outstanding advantage of the NVT plus test particle method when compared to the NpT plus test particle method. We apply the NVT plus test particle method to the Lennard-Jones 12-6 potential. We determine the coexistence curve far closer to the critical point than the result of the NpT plus test particle method. By applying the mixed-field finite-size scaling idea to our data, we obtain the critical temperature as T
c*=1.3207(4), the critical density as ρ
c*=0.316(1) and the critical pressure as p
c*=0.1288(5). These values for T
c*, ρ
c* and p
c* are the world-champion values since the error bars of these quantities are the smallest among those obtained so far.
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Naokazu Kitamura, Atsushi Oshiyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
1995-2011
Published: 2001
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We present total energy calculations for open edge growth mechanisms of carbon nanotubes using the density functional theory. Energies of polygonal networks, such as the pentagon, hexagon and heptagon on the armchair edge are calculated. Activation energies of the diffusion of the carbon adatoms on both the armchair edge and the zigzag edge are also investigated. In addition, the carbon adatoms can be adsorbed on the wall of the nanotubes. Thus, we calculate the adsorption energies of the carbon adatoms on the nanotube wall. On the other hand, the pentagon network on the nanotube edge which is responsible for the nanotube closure must be annealed out to the hexagon network to maintain the open edge growth. We discuss annealing out of the polygonal networks such as the pentagon by calculations of the activation energies to incorporate the adatom into the polygonal networks. From these calculations, it is found that the adatoms on the nanotube wall diffusing toward the nanotube edge play an important role of the open edge growth of the nanotubes.
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Yoichi Uehara, Yoshihide Suzuki, Hiroshi Komagata, Tohru Tsuruoka, Suk ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2012-2018
Published: 2001
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We have developed a theory of electron energy loss (EEL) spectra that includes the effects of sample surface roughness and the electromagnetic retardation. The energy loss probability is given by the sum of the term arising from a perfect flat surface and the contribution from surface roughness. The theoretical predictions are compared with experimental EEL spectra of an evaporated Au film. We find that the effects of both roughness and the electromagnetic retardation must be incorporated in the theory to understand the experimental spectra.
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Hiroki Fukuda, Hisazumi Akai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2019-2024
Published: 2001
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The hyperfine fields of Li impurities in ferromagnetic Ni are calculated by use of the Korringa-Kohn-Rostoker (KKR) Green's function method in the framework of the local spin density approximation (LSDA) and the supercell method. The electronic structure is self-consistently determined by taking account of the local lattice relaxation around the Li impurities. The calculated hyperfine field of Li at the substitutional site shows a good agreement with the experimentally observed hyperfine field. The local lattice relaxation gives rise to fairly large configurational changes in the surrounding host atoms in the case of the interstitial Li impurities, which in turn causes remarkable changes in the hyperfine fields at the Li nucleus. This indicates that it is crucial to take the local lattice relaxation into account for the light interstitial impurities in Ni.
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Toshifumi Itakura, Yoshikazu Suzumura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2025-2032
Published: 2001
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The commensurate-incommensurate transition, which occurs perpendicular to chains in quasi-one-dimensional quarter-filled spin density wave (SDW) state, has been examined within the classical treatment. By applying the renormalization group method,we derive phase diagram of commensurate and incommensurate states on the plane of temperature and the transverse misfit corresponding to the difference of phases between chains. The response functions for 2k
F SDW and 4k
F CDW (k
F being the Fermi wave vector) are calculated to examine the role of the misfit and the sign of commensurability energy. The relevance to the SDW state in (TMTSF)
2X salts is discussed.
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Tsuyoshi Hamada, Kunio Ishida, Hiroshi Kamimura, Yuji Suwa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2033-2037
Published: 2001
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In order to examine the Kamimura-Suwa model for the electronic structure of cuprates, computational study is made for a 4 × 4-site 2D square system. In this system the ground state of a dopant hole which is interacting with a two-dimensional quantum spin system is investigated numerically by the exact diagonalization method. Present numerical calculations show that antiferromagnetic ordering of the underlying host spins continues to exist even in the presence of a dopant hole. Allowing the dopant hole to adopt two kinds of orbital states through alternate Cu sites, the hole becomes itinerant, following the Kamimura-Suwa model. It is also shown in the case that the dopant hole occupies only a single orbital state b
1g, it tends to form a localized spin-polaron.
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Koichi Kusakabe
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2038-2048
Published: 2001
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By introducing a set of auxiliary equations representing a many-body system, we have derived an extension of the Kohn-Sham scheme for the density functional theory. These equations consist of a Kohn-Sham-type equation determining single-particle orbitals and an eigen-value equation for an effective many-body problem. A variational method similar to the Kohn-Sham technique was utilized to derive effective interactions as well as effective potentials without artificial substitution of a Hubbard-type interaction and a mean-field correction in the energy functional. The second equation is described by an effective many-body Hamiltonian with both 2-body interactions and mean-field terms. Rigorous formulation of the extended Kohn-Sham equation is also given in accordance with the Hadjisavvas-Theophilou formulation. Our formulation can be interpreted as a way to define models of the strongly correlated electron systems,
e.g. the Hubbard model.
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Satoshi Akamaru, Yosikazu Isikawa, Junji Sakurai, Kunihiko Maezawa, Hi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2049-2053
Published: 2001
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We have succeeded in growing a high-quality single crystal of PrNi
2Al
5, and have measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. Any magnetic phase transition has not been observed. The crystalline-electric-field (CEF) scheme has been estimated by using the reciprocal susceptibility and a magnetic part of the specific heat. The magnetic anisotropy has been well explained by the CEF effect. The analytical result of the CEF effect shows that this compound has a singlet ground state and that the CEF energy in 4f electrons from the ground state to the first excited state is 43 K. The Fermi surfaces and the cyclotron effective masses have been investigated by means of de Haas-van Alphen effect. It is found that the Fermi surfaces of PrNi
2Al
5 are almost the same as those of LaNi
2Al
5.
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Yoji Ohashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2054-2060
Published: 2001
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We investigate local characters of spin susceptibility around a nonmagnetic impurity in the normal state of high-T
c cuprate superconductors. In a model two-dimensional system with strong antiferromagnetic (AF) spin fluctuations and with an extended impurity potential which is finite not only at the impurity site but also around it, we find that the AF susceptibility and the uniform one are strongly enhanced around the impurity. In particular, the uniform susceptibility which is almost temperature-independent in the clean system remarkably increases with decreasing temperature. We also show that the local enhancement of the susceptibility is due to (1) an increase of the local density of states at the Fermi level near the impurity site, and (2) a mode-mode coupling effect which is caused by the impurity potential. Our results can explain the recent Knight shift measurements in YBa
2(Cu
1-xZn
x)
3O
6+y and YBa
2(Cu
1-xLi
x)
3O
6+y showing a Curie-Weiss temperature dependence of the uniform susceptibility at (around) the impurities, and also agree with the recent experiments on the nuclear spin-lattice relaxation rate in Zn-doped YBa
2Cu
3O
6+y and YBa
2Cu
4O
8 which observed anomalous enhancement of the low-energy AF spin fluctuations.
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Takeshi Usuki, Keigo Abe, Osamu Uemura, Yasuo Kameda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2061-2067
Published: 2001
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The ionic conductivity in liquid Ag-Se and Ag-Te systems has been measured using a residual potential technique. The ionic conductivity in the liquid Ag-Se system exhibits a local maximum at the stoichiometric composition of Ag
2Se. This maximum decreases rapidly with increasing temperature. The liquid Ag-Te system has also a higher value of the ionic conductivity around the composition of Ag
2Te, but a clear maximum as in the case of Ag-Se system cannot be observed even at lower temperatures. This may be considered to reflect a higher Ag
+ mobility at Ag
2Se just after melting. Such the difference of the ionic conduction near the melting point between both liquid systems, and in particular the unusual temperature dependence of ionic conductivity in the liquid Ag-Se system, could be due to the deference of the structural environment of Ag
+ in the system. The structural analysis of liquid Ag
2Se and Ag
2Te focusing on the environmental structure around Ag
+ has been made employing neutron structure factors previously observed, the result of which exhibits that there is a slight but significant difference of the configuration of Ag
+ in both liquids near the melting point, that is to say, Ag
2Se maintains the local order in the fast ion structure in the crystalline state, whereas, the fast ion structure in Ag
2Te largely changes on melting.
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Takasi Endo, Kouichi Toyoshima, Yutaka Hirayoshi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2068-2071
Published: 2001
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A quiet current with subshot noise is a regulated electron flow. When a time delay circuit, i.e. a low-pass filter is inserted into the flow, noise is generated in the high frequency region. By using a transistor circuit the noise generation due to the time delay is observed. A simple theoretical model explains the observed noise spectrum.
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Shokichi Kanno
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2072-2077
Published: 2001
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We have investigated the electric current through the extended states of quasi 2D substances having linear dimension larger than the collision length. We found that when the Fermi energy just coincides with the single particle energy of the extended states, the conductance is quantized as like the mesoscopic system for sufficiently low applied electric potential difference.
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Makoto Yoshida, Keiichi Koyama, Takahiro Tomimatsu, Makoto Shirakawa, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2078-2081
Published: 2001
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Cyclotron resonance (CR) measurements on a single crystal of LaBi have been performed in the temperature range from 1.6 to 30 K and at the frequency range from 50 to 190 GHz. The two CR absorption lines are observed for H||[100] at low temperature, which corresponds to effective masses m
CR* of 0.33m
0 and 0.65m
0, respectively. These values are in agreement with m
QO* of α-branch (0.4m
0) and γ-branch (0.63m
0) estimated from acoustic dHvA effect measurements.
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Youichi Ohno, Toshiyuki Wada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2082-2091
Published: 2001
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The misfit-layer compounds {(Pb
1-xSb
xS)
1+y}
mTS
2 (T=Ti and Nb; m=1 and 2) are constructed of the regular stacking of single or double two-atom-thick Pb
1-xSb
xS (Q) layers and a three-atom-thick TS
2 (H) layer. They are studied by means of the scanning tunneling microscope (STM) and the x-ray photoelectron spectroscopy (XPS) and the electron-energy-loss spectroscopy (EELS) methods. For the 2Q/1H (m=2) compounds, atomic-scale STM images are obtained from both the Q and H layers, whereas for the 1Q/1H compounds no STM images are obtained from a Q layer even if a Q layer consists of a (Pb,Sb)S layer. The electronic structures of the 2Q/1H compounds as well as the 1Q/1H compounds are discussed. It is found that as m increases, the x-ray photoemission threshold or the Fermi energy position shifts to lower binding energy by charge transfer from a Q layer.
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Naurang L. Saini, Antonio Bianconi, Hiroyuki Oyanagi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2092-2097
Published: 2001
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Here we provide a direct experimental evidence for critical local lattice fluctuations in the high T
c superconductors. Cu K-edge extended X-ray absorption fine structure (EXAFS) has been used to measure the distribution of Cu-O bond lengths and the amplitude of local lattice distortions in different materials with increasing chemical pressure on the CuO
2 layers. The stripe formation temperature T
co is determined by the upturn of the Debye Waller factor due to the onset of local lattice distortions. A decrease of the amplitude of lattice fluctuations at the superconducting transition reveals their role in the pairing mechanism. The dynamical lattice fluctuations in the normal phase for T>T
co show diverging lattice fluctuations at the critical chemical pressure Ε
c.
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Seiki Miyata, Kozo Osamura, Jun-ichi Suzuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2098-2101
Published: 2001
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The microscopic magnetic structure of a vortex in a Nb single crystal was investigated using small-angle neutron scattering by measuring higher order reflections. By fitting the experimental scattering intensities, the magnetic structure of a vortex can be represented by the London equation with an additional Gaussian factor due to the thermal displacement of vortices. The radius of a vortex (20.3 nm at 3.3 K) is somewhat smaller than the London penetration depth (λ
L(0)=31.5-39.0 nm).
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Tomio Koyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2102-2109
Published: 2001
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We derive Poisson's equation in the single-vortex state of type II superconductors in a conserved approximation in both dynamical and static cases. The charge and current vertex functions in the chain approximation are expressed in terms of the solutions of the Bogoliubov-de Gennes equation. We rigorously prove that these vertex functions satisfy the Ward-Takahashi relation. The vertex-correction in the chain approximation is, thus, consistent with the single-electron states satisfying the Bogoliubov-de Gennes equation in the single-vortex state. It is also shown that the vertex correction for the charge-charge correlation function vanishes in the static limit. The static vortex charge, thus, can be calculated by solving Poisson's equation in the lowest-order approximation.
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Takekazu Ishida, Kentaro Kitamura, Kiichi Okuda, Hidehito Asaoka
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2110-2113
Published: 2001
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We examine the effective regime for intrinsic pinning of an YBa
2Cu
3O
6.94 single crystal in the H - T plane. The irreversibility line for intrinsic pinning can be tracked by the hysteresis of the magnetic torque when the field is almost in parallel to the ab plane. The melting transition in the H ⊥ c configuration appears at higher temperatures where the intrinsic-pinning peak is absent. We argue that the intrinsic pinning may not affect the nature of the vortex melting transition in the H ⊥ c configuration.
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Tomio Koyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2114-2123
Published: 2001
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We present a theory for the c-axis charge dynamics in a stack of underdamped intrinsic Josephson-junctions with a finite in-plane area, W. It is shown that the size effect with respect to W can be described as a quantum effect in the phase dynamics of a Josephson-junction array. We derive rigorously the capacitance matrix of a 1D Josephson-junction array on the basis of the time-dependent Ginzburg-Landau model at T=0 K. The long range part of the Coulomb interaction between superconducting charges induces the plasma oscillations with a finite gap propagating along the c-axis. The plasma oscillations, which are stable in systems with large W, become unstable at a critical in-plane area, W
c, as the in-plane area decreases. The instability is caused by the Coulomb blockade effect. In the systems with W<W
c the single Cooper-pair tunneling dominates the charge dynamics. We develop a renormalization group theory for the charge dynamics of a 1D array of Josephson-junctions and derive the explicit expression for W
c. In the limit of small W our theory predicts the charge soliton state. The size of the charge soliton is related to the charge screening length of the superconducting electron system. The edge voltage in the charge soliton state is proportional to the number of junctions in an array.
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Yoshiharu Kanegae, Yoji Ohashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2124-2133
Published: 2001
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Atomic-scale superconductor/ferromagnet (S/F) and superconductor/antiferromagnet (S/AF) multilayered systems are investigated in order to clarify the stability of the π-phase where the phase difference of the superconducting (SC) order parameter between neighboring SC layers is π. We clarify the stable region of this phase in the phase diagram with respect to temperature and exchange field (B) in magnetic layers. In the phase diagram, we show that the π-phase appears in both the S/F and S/AF cases. In particular, although a previous work reported that the π-phase is not obtained for any reasonable value of B in the S/AF case where the band structure in the normal state of SC and magnetic layers are metallic and identical with each other, we find in this case that the stable region of the π-phase is as wide as that in the S/F case under a certain condition. We also investigate how the π-phase is affected by detailed band structures and the symmetry of SC order parameter, and discuss the possibility of this phase in the layered magnetic superconductor, RuSr
2GdCu
2O
8.
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Sanshiro Sako, Kazunari Ohshima, Masahiro Sakai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2134-2138
Published: 2001
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The particle size dependence of Néel temperature was investigated in a thin CoO shell of an oxide passivated Co particle. In addition to the blocking effect of the exchange anisotropy interaction, the influence of the magnetic dipole interaction between neighbouring Co cores to the blocking temperature T
B was examined by measuring the zero field cooling magnetic susceptibility in dense oxide passivated nanosized Co particles dispersed uniformly on two dimensional plane without coagulation. The blocking temperature dominated by the dipole-dipole interaction was discussed in relation to the transition temperature to the spin-glass like collective state.
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Julián G. Sereni
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2139-2150
Published: 2001
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Three types of magnetic phase diagrams as a function of composition or pressure, f(z,p), are identified among Ce systems: I) with the ordering temperature T
ord→ 0 monotonously, followed by a
narrow region where non-Fermi-liquid (NFL) behavior is observed; II) with T
ord vanishing at finite temperature, but followed by an
extended NFL region, and III) where T
ord remains nearly constant. Among the analyzed systems intrinsic differences are found in the evolution of their respective properties, namely: in
group-I an increase of the density of excitations is observed below T
ord. In
group-II the evanescense of T
ord(z,p) coincides with the extrapolation to zero of the magnetic free energy (Δ G → 0), and the existence of a
reference function implying that T
K≠ f(z,p), whereas T
ord=f(z,p). Finally,
group-III is also characterized by the evanescense of T
ord where Δ G → 0, but in this case T
ord≠ f(z,p) whereas T
K=f(z,p). The characteristics of each group are discussed and compared together with the different C
p(T)/T dependencies at T≥ T
ord and some related scalings, which allow to recognize a
quasi-paramagnetic phase.
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Hiroki Nakano, Seiji Miyashita
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2151-2157
Published: 2001
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Low-temperature magnetization process of the nanoscale iron cluster in linearly sweeped fields is investigated by a numerical analysis of time-dependent Schrodinger equation and the quantum master equation. We introduce an effective basis method extracting important states, by which we can obtain the magnetization process effectively. We investigate the structure of the field derivative of the magnetization. We find out that the antisymmetric interaction determined from the lattice structure reproduces well the experimental results of the iron magnets and that this interaction plays an important role in the iron cluster. Deviations from the adiabatic process are also studied. In the fast sweeping case, our calculations indicate that the nonadiabatic transition dominantly occurs at the level crossing for the lowest field. In slow sweeping case, due to the influence of the thermal environment to the spin system, the field derivative of the magnetization shows an asymmetric behavior, the magnetic Fohn effect, which explains the substructure of the experimental results in the pulsed field.
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Ram Kripal, Sanjay Misra
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2158-2160
Published: 2001
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Electron spin resonance (ESR) of Cu
2+ doped calcium propionate has been studied at room temperature. Spin Hamiltonian parameters are calculated from the ESR absorption spectra which are g
x=2.1285± 0.002, g
y=2.1868± 0.002, g
z=2.2205± 0.002, A
x=(121± 2)× 10
-4 cm
-1, A
y=(140± 2)× 10
-4 cm
-1 and A
z=(142± 2)× 10
-4 cm
-1. It is found that Cu
2+ enters the lattice interstitially. The ESR results indicate that the copper complex possesses rhombic symmetry. The ground state wave function of Cu
2+ ion in this lattice is also determined from the spin-Hamiltonian constants obtained from ESR results. It is found that the ground state is predominantly |x
2-y
2›.
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Michinobu Mino, Philip E. Wigen
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2161-2163
Published: 2001
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Parametrically excited spin waves in an yttrium iron garnet (YIG) are good model objects to study nonlinear dynamics. Chaotic oscillations of this system can be controlled with a time-delayed feedback method. The feedback perturbation was added to the static magnetic field. This controlling process has been characterized by strange attractors. With increasing feedback gain, a fractal dimension of the strange attractor decreases from 2.9 to 1.1. This means that chaotic oscillations change to periodic oscillations successively. Further increase of feedback gain eventually produces chaotic oscillations again.
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Aleksandra B. Djurišic, E. Herbert Li
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 7 Pages
2164-2167
Published: 2001
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In this work we propose an analytical expression for the complex dielectric function which includes both discrete and continuum exciton effects. The proposed analytical model takes into account accurately the excitonic effects, while it satisfies the requirements that the imaginary part of the dielectric function is an odd function of energy, and the real part of the dielectric function is an even function. We show that accurate introduction of broadening leads to equations for the dielectric function containing only elementary functions, with terms dependent on the exciton order m describing discrete exciton states. The proposed model describes well the experimental data for the absorption edge of GaN.
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