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Yuan-Fa Cheng, Bi-Bo Jiang
Article type: Others
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
313-316
Published: 2001
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In a hydrogen-bonded molecular chain with a symmetric double-well potential, using the variational approach, we study the kink pair with anharmonic interatomic interactions in the two sublattices, based on the two-component soliton model. We obtain the asymmetric solutions of a kink pair and calculate the energy, the effective mass and the charge density of a kink pair due to anharmonicity. The calculated results are in good agreement with the experimental data.
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Tadahiko Chida, Shugo Suzuki, Kenji Nakao
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
317-320
Published: 2001
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We show that charge fluctuation occurs in A
3C
60 due to the competition between electron-electron and electron-phonon interactions and consequently the material remains metallic although both interactions are considerably strong. We calculate the spectral density for A
3C
60 based on the dynamical mean-field theory by using the exact diagonalization method. We find a satellite, which is a direct consequence of the charge fluctuation, at about 1.3 eV below the Fermi level. We point out that high-resolution photoemission experiments have shown the existence of this satellite.
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Chisa Hotta, Hidetoshi Fukuyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
321-324
Published: 2001
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A possible phase diagram of the family of two-dimensional organic conductors, κ-ET
2X, has so far been characterized by the strength of the mutual on-site Coulomb interaction relative to the bandwidth. In this paper, it is pointed out that there is another important parameter to categorize members of this family with quarter-filled hole bands under strong dimerization. The key parameter turns out to be the degree of splitting of the anti-bonding highest occupied molecular orbital (HOMO) bands which determines the shape of the Fermi surface, and then the possible importance of the nesting, which leads to the stability of different types of the ground states, Mott insulator and spin-density-wave (SDW) is pointed out.
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Harukazu Kato, Takeshi Waki, Masaki Kato, Kazuyoshi Yoshimura, Koji Ko ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
325-328
Published: 2001
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From the resistivity and magnetic susceptibility measurements of polycrystalline Bi
xV
8O
16 with 1.6<x<1.8, it was revealed for the first time that Bi
xV
8O
16 with 1.72<x<1.8 exhibits a temperature-induced metal-insulator transition (MIT). A large hysteresis was observed in their susceptibilities and resistivities as functions of temperature, indicating that the MIT is of the first order. The possibility of charge ordering between V
3+ and V
4+ has been discussed for the origin of the MIT in this system. In the insulating phase, Bi
xV
8O
16 with 1.72<x<1.8 indicates another anomaly in the magnetic susceptibility, which may imply magnetic ordering below the anomaly temperature. We suggest that the physical properties of this system are controlled by multiple order parameters including charge, spin, and orbital quanta.
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Yasumoto Tanaka, Akira Iyo, Naoki Shirakawa, Minoru Ariyama, Madoka To ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
329-332
Published: 2001
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Specific heat anomaly was studied on Cu
xBa
2Ca
3Cu
4O
y. ΔC/T
c, a height of peak of the specific heat at the superconducting transition (T
c) divided by T
c, is less than 60% of that of optimally doped YBa
2Cu
3O
7-δ. This suggests that a large density of states (DOS) remains to prohibit the creation of Bardeen-Cooper-Schrieffer (BCS) pairs at T
c. It is much larger than the residual DOS at 0 K. We interpret that the “
missing DOS” start to become BCS pairs at a temperature lower than T
c, as proposed by an NMR study [Phys. Rev. B
61 (2000) 9707], though we have not yet seen clear evidence of this.
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Hiroyuki Takagiwa, Jun Akimitsu, Hazuki Kawano-Furukawa, Hideki Yoshiz ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
333-336
Published: 2001
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The coexistence of antiferromagnetism and superconductivity in the hybrid ruthenate-cuprate RuSr
2YCu
2O
8 synthesized under high pressure has been confirmed by means of powder neutron diffraction and resistivity measurements. The Ru moments are antiferromagnetically ordered at about 149 K and Ru spins can be aligned by applying a magnetic field, suggesting that the system gradually changes from antiferromagnetism to ferromagnetism. However, the superconductivity in the compound persists even at H=9 T. This indicates the coexistence of ferromagnetism and superconductivity under a high magnetic field.
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Yoshiei Todate
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
337-340
Published: 2001
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Measurements of magnetic susceptibility and magnetic neutron diffraction on powder of ordered complex perovskite Ba
2CuWO
6 have been performed. This compound was expected to be the two-dimensional antiferromagnet with frustrating nearest and next-nearest-neighbor antiferromagnetic interactions. It has been shown that the susceptibility is well fitted by the high-temperature series expansion calculations for the nearest-neighbor square lattice antiferromagnet with S=1/2 and J=-55.5±0.2 K. On the other hand, neither the antiferromagnetic Bragg peak nor clear magnetic diffuse scattering expected for the two-dimensional antiferromagnetic spin correlation has been detected at 15 K. Effects of the frustration in the case of the finite nearest-neighbor interaction are discussed.
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Tomoaki Moriwaka, Takashi Nishioka, Noriaki K. Sato
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
341-344
Published: 2001
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CaB
6 doped with a La atom, Ca
1-xLa
xB
6, is a ferromagnet, but the magnetic and transport properties of the nondoped mother material, CaB
6, remain unclear. In order to reveal these we prepared a nondoped sample of CaB
6 from CaO and B by the oxidation-reduction method. We observed that a sample synthesized at an appropriate temperature shows a diamagnetic magnetization, while a sample prepared at a higher temperature exhibits ferromagnetism which is one order of magnitude larger than that in La-doped CaB
6. We have ascribed this appearance of ferromagnetism to Ca vacancies which were produced during the synthesis. When we compared experimental results of the electrical resistivity with the magnetic properties, we failed to find any correlation between them. From these observations, we wish to suggest that the Ca vacancy yields not only the carrier doping effect but also another effect such as inhomogeneity or lowering of local symmetry in the crystal, the latter being possibly more effective in terms of the appearance of the ferromagnetism.
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Yoshihiro Murayama, Masaki Sano
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
345-348
Published: 2001
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The elastic force for a single DNA molecule (15.7 kilobasepairs) during a transition between an elongated coil and a collapsed globule state was measured by dual-trap optical tweezers. Under highly diluted conditions, the DNA concentration was 2 nM in nucleotides, the force change in a collapsing process and the elastic response in the collapsed state were observed at the single molecule level. To induce the transition, a trivalent cation, spermidine, was used. Two types of force changes in different timescales occurred in the intramolecular collapsing process; a fast force change from about 0.2 to 0.9 pN within 20 s, and a slow force change from 0.9 to 1.5 pN for 100 s. After the force change, a force plateau at about 1.8 pN was observed in a stretching process; however, after the process, the elastic response was the same as the one in a coil state. This hysteresis indicates the existence of a metastable state such as a supercooling liquid state.
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Koh Hashimoto, Takashi Ikegami
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
349-352
Published: 2001
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A replicator equation with mutation processes is numerically studied. Without any mutations, two characteristics of the replicator dynamics are known: 1) the closer a system approaches a heteroclinic cycle, the exponentially longer a single species dominates a population and 2) there is coexistence of different heteroclinic cycles. A mutation introduces some new aspects: the emergence of structurally stable attractors and chaotic itinerant behavior. In addition, it is reported that a neutral attractor can exist in the μ → +0 region.
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Toshiya Iwai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
353-358
Published: 2001
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Stochastic resonance (SR) is numerically analyzed by the method of stochastic energetics. The work done by the external agent which drives the potential to fluctuate periodically is shown to be a good quantitative measure to detect SR. On the other hand, signal-to-noise ratio (SNR) is shown to be not a good quantitative measure of SR by comparison with the work.
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Norio Inui, Makoto Katori, Faqir M Bhatti
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
359-366
Published: 2001
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Domany-Kinzel (DK) model is a family of the 1+1 dimensional stochastic cellular automata with two parameters p
1 and p
2, which simulate time evolution of interacting active elements in a random medium. By identifying a set of active sites on the spatio-temporal plane with a percolation cluster, we discuss the directed percolation (DP) transitions in the DK model. We parameterize p
1=p and p
2= α p with p ∈ [0,1] and α ∈ [0,2] and calculate the mean cluster size and other quantities characterizing the DP cluster as the series of p up to order 51 for several values of α by using a graphical expansion formula recently given by Konno and Katori. We analyze the series by the first- and second-order differential approximations and the Zinn-Justin method and study the dependence on α of the convergence of estimations of critical values and critical exponents. In the mixed site-bond DP region, 1 ≤ α ≤ 1.3553, the convergence is excellent. As α → 2 slowing down of convergence and as α → 0 peculiar oscillation of estimations are observed. This paper is the first report of the systematic study of DK model by series expansion method.
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Kazumitsu Sakai, Zengo Tsuboi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
367-371
Published: 2001
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The thermodynamic Bethe ansatz (TBA) equation for an integrable spin chain related to the Lie superalgebra osp(1|2) is analyzed. The central charge determined by low temperature asymptotics of the specific heat can be expressed by the Rogers dilogarithmic function, and identified to be 1. Solving the TBA equation numerically, we evaluate the several thermodynamic quantities. The excited state TBA equation is also discussed. These results supplement our previous papers: [Mod. Phys. Lett. A
14 (1999) 2427; Int. J. Mod. Phys. A
15 (2000) 2329].
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Takao Yoshinaga, Koji Kotani
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
372-375
Published: 2001
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Nonlinear evolution equations for a planar liquid sheet in a void are analytically derived through the modified membrane approximation when the finite thickness of the sheet is considered, where modification is made for the evaluation of the pressure term in the momentum equations. It is found that the equations thus derived are coincident with the equations obtained through the power series expansion method with respect to the sheet thickness. It is also found that this modification is effective, in particular, for the dilational mode waves in comparison with our previous results.
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Takahiro Iwayama, Takeshi Watanabe, Theodore G. Shepherd
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
376-386
Published: 2001
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The low wave number range of decaying turbulence governed by the Charney-Hasegawa-Mima (CHM) equation is examined theoretically and by direct numerical simulation. Here, the low wave number range is defined as values of the wave number k below the wave number k
E corresponding to the peak of the energy spectrum, or alternatively the centroid wave number of the energy spectrum. The energy spectrum in the low wave number range in the infrared regime (k → 0) is theoretically derived to be E(k) ∼ k
5, using a quasinormal Markovianized model of the CHM equation. This result is verified by direct numerical simulation of the CHM equation. The wave number triads (k,p,q) responsible for the formation of the low wave number spectrum are also examined. It is found that the energy flux Π(k) for k< k
E can be entirely expressed by Π
(-)(k), which is the total net input of energy to wave numbers <k arising from interactions with wave numbers p, q > k. Furthermore, the contribution of nonlocal triad interactions to the energy flux is found to be predominant in the range log(k/k
E)<-0.5, where the nonlocal interactions are defined to be those triad interactions for which the ratio of the largest leg of the triad to the smallest leg is larger than four.
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Christine Fernandes Xavier, Roberto Antonio Clemente
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
387-393
Published: 2001
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An hydrodynamic model for single bubble sonoluminescence (SBSL) taking into account dissociation in diatomic gases and ionization in monoatomic ones is presented. Bubble inertial effects are neglected and a uniform interior approximation is employed. The Gilmore approximation for the bubble radius equation is used and heat conduction at the bubble boundary is included in
ad hoc way. Dissociation and ionization are included in a self-consistent way in the gas energy equation by relaxing the commonly used thermodynamic equilibrium hypothesis and introducing proper rate equations. The cases of oxygen and nitrogen bubbles are considered, showing that an appreciable amount of dissociated moleculae should be produced when O
2 fills the cavity while dissociation should be negligible in the case of N
2. All inert gases are also considered and it is shown that ionization levels should be very low in the case of He and Ne, while an appreciable increasing amount of ionized atoms should be produced in Ar, Kr, Xe and Rn bubbles. The obtained maximum gas temperatures for monoatomic gases are all close to 20000 K, thanks to a special combination of heat conduction and ionization effects, corroborating some theoretical previsions on SBSL light emission mechanism based on free electron transitions.
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Katsunori Yoshimatsu, Mitsuaki Funakoshi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
394-406
Published: 2001
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Resonantly forced water waves in a square container due to its horizontal oscillations are examined. The excited waves are assumed to be gravity waves for infinite depth. Using the reductive perturbation method and including the effect of a linear damping, we derive an evolution equation for the complex amplitudes of two degenerate resonant modes. When the angle θ between the direction of the oscillations and that along one of the sidewalls of the container is 0
º or 45
º, we obtain planar stationary solutions without the rotation of wave pattern as well as a pair of non-planar ones associated with the clockwise or anti-clockwise rotation. If 0
º < θ < 45
º , however, no planar stationary solution exists, and the symmetry between these non-planar solutions for θ=0
º or 45
º is broken. We find the pitchfork bifurcations of the stationary solution for θ=0
º and 45
º, and also the Hopf and saddle-node bifurcations of this solution for 0
º ≤ θ ≤ 45
º. Furthermore, periodic or chaotic solutions exist within the parameter region of no stable stationary solution for any θ. The obtained bifurcations of the stationary solutions are found to be a little more complicated than those for a circular cylinder.
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Atsushi Furuya, Sanae-I. Itoh, Masatoshi Yagi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
407-414
Published: 2001
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Tearing mode instability in the presence of microscopic turbulence is investigated. The effects of microscopic turbulence on global MHD mode are taken as drags which are calculated by one-point renormalization method and mean-field approximation. These effects are reduced to effective ion viscosity, resistivity and thermal conductivity in reduced MHD equations. Using these equations, the stability analyses of the tearing mode are performed. It is shown that a finite amplitude of fluctuation enhances the growth rate of tearing mode. For very high values of turbulent diffusivities, marginally stable state exists. The effects of each turbulent diffusivity on mode stability are examined near marginal stability boundary. Parameter dependence on the growth rate of tearing mode is analyzed with/without the microscopic turbulence. For the microscopic turbulence, a resistive ballooning mode (RBM) turbulence and ion temperature gradient (ITG) turbulence are considered as examples.
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Shinsuke Maki, Sadao Masamune, Hiromi Kajikawa, Junya Sekikawa, Hideki ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
415-420
Published: 2001
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The edge toroidal reversed current outside the field reversal surface manifestly plays some important roles in reversal field pinches (RFPs). The crucial roles of the edge reversed toroidal current has included the implication of the deep field reversal in the recently attained improved confinement modes in some RFPs. We have concentrated our attention on the formation mechanism of the reversed edge toroidal current in the STP-3M reversed field pinch. Measurements of fast electron current and floating potential have revealed minutely that the reversed edge toroidal current is driven by fluctuational transport of superthemal electrons produced in the core region. Time evolution of the floating potential, measurement of the space potential profile, has shown the radially outerward electric field, an indication of the preferential loss of electrons from the core region. The dominance of the core resonant modes in the toroidal mode power spectrum of the edge magnetic fluctuations indicates the stochastic magnetic field line in the core region. This is to the evidence that the origin of the edge fast electrons is the stochastic diffusion of fast electrons produced in the core region.
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Ken Kajiwara, Teruo Saito, Yoshinori Tatematsu, Yasuhito Kiwamoto, Hir ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
421-427
Published: 2001
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This paper presents a picture of current flow relevant to the plug/barrier cell and an end plate installed on the end wall of the GAMMA 10 tandem mirror. Detailed analyses show that, during electron cyclotron resonance heating for plug potential formation, a net electron current flows through the end plate. In the plug/barrier cell, on the other hand, ion currents are detected during ECRH on ring electrodes newly installed near the side wall of the vacuum vessel. A part of the radial ion currents is connected to the axial net electron current flowing through the end plate. This indicates that a residual non-ambipolar diffusion still remains. The radial ion current in the plug/barrier cell includes another component that originates form the axial ion flux emanating from the central region. This suggests radial diffusion of ions during potential plugging.
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Sergey V. Dmitriev, Miki Yajima, Yoshiya Makita, Denis A. Semagin, Koh ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
428-436
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We report the results of molecular-dynamics calculation of equilibrium modulated phases of quartz in the vicinity of pressure induced α -β transition. A numerical method suitable for simulation of modulated phases in the vicinity of transition point was developed. The phase diagram with respect to the unit cell deformations was obtained from the pairwise interatomic potentials by [Tsuneyuki
et al.: Phys. Rev. Lett.
61 (1988) 869]. The results show that the modulated structures with various wavevectors appear between α- and β-phases suggesting that the softening may occur at any point on the Σ line in the Brillouin zone and that a structure with large wavevector seems to be more probable than one with a small wavevector.
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Kazutaka Kudo, Satoru Ishikawa, Takashi Noji, Tadashi Adachi, Yoji Koi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
437-444
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We have systematically measured the thermal conductivity κ of Sr
14-xA
xCu
24O
41 (A=Ca, La: 0≤ x(Ca) ≤ 9: 0 ≤ x(La) ≤ 5) single crystals, in order to investigate the spin gap and hole pairing. The observed κ has been analyzed to be composed of κ
ph, κ
spin and κ
hole due to phonons, spins and holes, respectively. The contribution of κ
spin is observed only along the c-axis except for x(Ca) ≥ 6. The spin gap in the ladder estimated from κ
spin is ∼400 K and independent of x. This is regarded as corresponding to the spin excitation from spin-singlet to spin-triplet, as those estimated from the neutron scattering and Raman scattering measurements. The contribution of κ
hole is observed at high temperatures for larger x(Ca) values. The activation energy of holes in the ladder estimated from κ
hole decreases with increasing x(Ca). This is regarded as corresponding to the dissociation of hole pairs, as that estimated from the electrical resistivity measurements. These results are consistent with the recent suggestion that most of holes are paired and localized in the ladder at low temperatures.
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Rie Haruki, Makoto Seto, Shinji Kitao, Yasuhiro Kobayashi, Yoshitaka Y ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
445-448
Published: 2001
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The effect of the diffusive motion in a short time range on the nuclear resonant quasielastic scattering spectrum is presented. The solution of the Langevin equation, which describes the motion of the diffusing particle in a short time range as well as that in a long time range, was applied to analyze the nuclear resonant scattering spectrum of Fe cations in Nafion membranes instead of the solution of the generally-used simple diffusion equation which does not describe the diffusive motion in a short time range correctly. It made improvements in the fitting especially at the wings of the data as compared with the solution of the simple diffusion equation. The characteristic time of the diffusive motion of Fe ions in Nafion is estimated to be about 10
-14 s. By the detailed analysis of the high energy part of nuclear resonant scattering spectrum, it is possible to reveal diffusive motion even in the short time range as ∼10
-14 s.
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Doan Nhat Quang, Nguyen Huyen Tung
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
449-459
Published: 2001
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A theory is presented of the density of states (DOS) over the entire energy spectrum of the disordered quasi-one-dimensional electron gas (1DEG) in a quantum wire. The disorder is caused by Gaussian random fields of any origin, especially those of short range. The solution is derived by means of a 1D version of the path-integral technique within the approximation based on a non-local harmonic modeled action. A simple analytic expression for the 1D DOS and different variational equations for the curvature of the trial well are then obtained, where the autocorrelation function of the random field plays the key role as the input function for disorder interaction. This enables us, for the first time, to examine in detail the effect from disorder of various origins on the DOS of 1DEG's in quantum wires of arbitrary geometry as well as to incorporate the many-body screening by 1DEG's. The theory is verified by reproducing the well-known asymptotics of the white-noise energy spectrum given by earlier theories. Numerical calculations have been carried out with inclusion of the local-field correction due to exchange and correlation in the 1DEG for a modulation-doped cylindrical quantum wire from GaAs/Al
xGa
1-xAs.
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Hideto Fukazawa, Yoshiteru Maeno
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
460-467
Published: 2001
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We have grown single crystals of electron doping system Ca
2-xLa
xRuO
4 (0.00 ≤ x ≤ 0.20) by a floating zone method. The first order metal/non-metal transition and canted antiferromagnetic ordering occur for 0.00 < x < 0.15, similar to those in the bandwidth controlled system Ca
2-xSr
xRuO
4 (CSRO). However, comparing with CSRO, we found a rather different metallic ground state adjacent to the non-metallic ground state with canted antiferromagnetic order. Instead of short-range antiferromagnetic correlation found in CSRO (0.20 ≤ x < 0.50), the metallic ground state of the present system is characterized by strong ferromagnetic correlation.
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Katsurou Hanzawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
468-480
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We address the question as to how the coexistence and the fluctuation of the interactions affect the properties of phase I and II in CeB
6. For that purpose, we develop the theory of the constant coupling approximation for the coexistent system of the interaction of O
xy-type quadrupole moments and that of T
xyz octupole moment, including the Zeeman effect. It is shown that the increase of the transition temperature between phase I and II with increasing applied magnetic field is caused mainly by the cooperation of the O
xy and the T
xyz interactions. The pronounced features of the specific heat and the magnetization are reproduced, because both the effects of coexistence and fluctuation of the interactions are taken into account in the present calculation.
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Masatsura Igami, Takeshi Nakanishi, Tsuneya Ando
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
481-491
Published: 2001
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An effective-mass theory is developed on transport of non-doped carbon nanotubes with local and short-range impurities in the presence of a magnetic field. The conductance is shown to be scaled completely by the field component in the direction of impurities. In a weak-field regime, the conductance strongly depends on strength of potential and the difference in the number of impurities at A and B sublattices Δ N
AB. In a strong-field limit, the conductance is reduced to e
2/π\hbar if impurities exist only on A or B sublattices and vanishes in all other cases. These results are intuitively understood by localized charge distribution of the wave function in magnetic fields.
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Daichi Matsumoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
492-497
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The transport in a superconductor-quantum-dot-superconductor system is studied analytically using a simple perturbation theory. The dc Josephson current through a quantum dot depends on the phase difference and the binding energy of the localized excited states, is not always a sine curve and is also influenced greatly by the competition between the superconductivity and the Kondo effect. π junction is shown analytically.
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Yositake Takane
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
498-504
Published: 2001
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Fluctuation paraconductivity slightly above the superconducting transition temperature is studied theoretically in mesoscopic structures connected to massive normal-metal probes. The paraconductivity, consisting of the Aslamazov-Larkin (AL) and Maki corrections, is shown to modify spatial voltage distribution. A simple method is presented for the calculation of voltage difference in quasi-one-dimensional multilead structures. It is shown that due to the nonlocal AL correction, finite voltage difference arises despite the absence of net current between two voltage probes. It is also shown that spatial variation of the AL and Maki corrections can be detected by voltage measurements with two sets of voltage probes.
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Junji Sakurai, Tomohiko Kuwai, Dexuan Huo, Teruo Ono, Kunji Shigeto, T ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
505-508
Published: 2001
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We have measured the electrical resistance R of wires and foils of thin artificial Cu/Permalloy (NiFe) layers in the temperature range from 0.1 K to 200 K under magnetic fields up to 10 tesla, and the thermoelectric power S from 2 K to 200 K. The logarithmic increase of R in the low temperature range (below 20 K for example) was observed for all the present samples. This increase of R was found to stay unchanged even under a strong magnetic field of as much as 10 tesla. The curves of S as a function of temperature T showed a normal metal behavior without any Kondo type anomaly. Possible origins of the logarithmic increase of R are discussed.
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Atsuya Kumagai, Masahiko Hayashi, Hiromichi Ebisawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
509-512
Published: 2001
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We study the two-dimensional spin-charge separated Ginzburg-Landau (GL) theory containing U(1) gauge interactions as a semi-phenomenological model describing fluctuating condensates in high temperature superconductivity. Based on the original GL action, we derive the effective action of Cooper pair. Especially, we clarify how Cooper pair correlation evolves in the normal state from the point of view of spin-charge separation. Furthermore, we show how Cooper pair couples to gauge field in a gauge-invariant way, stressing the insensitivity of Cooper pair to infrared gauge field fluctuation.
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Yasuhisa Ushida, Takashi Nishioka, Masaaki Kontani, Noriaki K. Sato
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
513-520
Published: 2001
Released on J-STAGE: February 28, 2003
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We have measured specific heat in magnetic fields, magnetization at ambient and high pressures and magnetostriction of Ce
5Si
3 and its alloy system (Ce
1-xLa
x)
5Si
3. As temperature is lowered, the systems for x < x
c ∼ 0.15 undergo successive phase transitions, while those for x > x
c exhibit only a spin-glass transition. From the obtained experimental results, we have constructed phase diagrams, magnetic field versus temperature for Ce
5Si
3 and temperature versus La-concentration for (Ce
1-xLa
x)
5Si
3. The measurements of the magnetization have revealed that the metamagnetism occurs for field directions of H || a as well as H || c. We discuss an origin of the metamagnetism on the basis of a crystalline electric field model and thermodynamic analysis.
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Tomoya Kuromaru, Hiroaki Kusunose, Yoshio Kuramoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
521-531
Published: 2001
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Elastic constants of a single-impurity model with the Γ
8 ground state is studied with particular attention to the anisotropy induced by external magnetic field. We calculate elastic constants C
66 and C
44 taking account of deformations to second order. Under external magnetic field, field-induced quadrupole moments affect elastic constants through the coupling with second-order terms of deformations. It is shown, with an appropriate choice of coupling parameters, that the C
66 decreases with increasing magnetic field parallel to the (001)-axis. This single-ion model can also explain the splitting of the C
44-modes observed in ultrasonic measurement of Ce
0.5La
0.5B
6.
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Seizo Watarai, Seiji Miyashita, Hiroyuki Shiba
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
532-537
Published: 2001
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Because of the frustration the spin structure of hexagonal Heisenberg antiferromagnets, which have weak XY-like anisotropy and ferromagnetic interlayer coupling, is determined by a delicate balance. The Monte Carlo method (for classical spins) is applied to obtain the phase diagram. It is shown that a competition between weak XY-like anisotropy and entropy effect (i.e.,thermal fluctuations) results successively in various phases, which show up in the magnetization process. At high fields a coplanar spin structure is stabilized at finite temperatures, while only one phase with the umbrella-type spin structure is present in the ground state. For a comparison the phase diagram of the Heisenberg model without anisotropy is also studied to find the same field-induced phase at high fields. In the low field region, the spin structure in the Heisenberg model is different from that in the XY-like case. We find entropy-induced phase transitions to occur due to thermal fluctuations, which overcome the weak anisotropy.
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Dai Aoki, Norihito Suzuki, Kousaku Miyake, Yoshihiko Inada, Rikio Sett ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
538-546
Published: 2001
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We have grown a single crystal with the residual resistivity ratio of 81, and studied its electronic properties of the cubic antiferromagnetic compound UGa
3. From the transverse magnetoresistance experiments, UGa
3 has been found to be a compensated metal with equal carrier numbers of electrons and holes. In the de Haas-van Alphen experiments we have detected nine closed Fermi surfaces. Detected cyclotron effective mass is relatively large, ranging from 2.3 to 9.4 m
0. The topology of the Fermi surface is compared to the result of energy band calculations.
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Beat Ammon, Masatoshi Imada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
547-557
Published: 2001
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Different models for doping of two-orbital chains with mobile S=1/2 fermions and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the S=1 spins are investigated by density matrix renormalization group (DMRG) methods. The competition between antiferromagnetic (AF) and FM order leads to a rich phase diagram with a narrow FM region for weak AF couplings and strongly enhanced triplet pairing correlations. Without a level difference between the orbitals, the spin gap persists upon doping, whereas gapless spin excitations are generated by interactions among itinerant polarons in the presence of a level difference. In the charge sector we find dominant singlet pairing correlations without a level difference, whereas upon the inclusion of a Coulomb repulsion between the orbitals or with a level difference, charge density wave (CDW) correlations decay slowest. The string correlation functions remain finite upon doping for all models.
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Yoshihiko Inada, Piotr Wisniewski, Masao Murakawa, Dai Aoki, Kousaku M ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
558-568
Published: 2001
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We measured the transverse magnetoresistance and de Haas-van Alphen (dHvA) oscillation in the ferromagnetic compounds U
3As
4 and U
3P
4. The magnetoresistance in both compounds increases as a function of H
n (n ∼eq 2) in a wide angular region, indicating that U
3As
4 and U
3P
4 are compensated metals. As for U
3P
4, the angular dependence of the magnetoresistance shows clearly dips for particular field directions. This implies the existence of a multiply-connected Fermi surface which favors open orbits along the ‹110› and ‹112› directions. We also detected several dHvA branches in U
3As
4 and U
3P
4. Most of them are due to the closed Fermi surfaces, which are explained by recent results of fully relativistic spin-polarized LMTO band calculations. The cyclotron effective mass is large, ranging from 5 to 70 m
0, and consistent with the electronic specific heat coefficient of 83 mJ/K
2·mol in U
3As
4 and 90 mJ/K
2·mol in U
3P
4.
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Takashi Yoshida, Hiroyuki Mashiyama, Tomoyuki Mochida
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
569-575
Published: 2001
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The low temperature phase of betaine phosphate was investigated by X-ray diffraction. The intensity of the X-ray diffraction at 20 K was measured and analyzed to determine the crystal structure. The least-squares method converged at the R factor 4.6% with 3349 reflections (4.2% for 2081 normal reflections and 8.4% for 1268 superlattice reflections). The structure analysis clarified that the protons (the hydrogen atoms of the phosphate origin) between neighboring phosphate tetrahedrons were in order in the low temperature phase causing the super structure of cell-doubling. The temperature dependence of superlattice reflections was measured and a kink was found corresponding to the intermediate phase between 76 K and 85 K.
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Ehtesanul Islam, Akira Sakai, Akira Onodera
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
576-581
Published: 2001
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Micro-probed Raman scattering spectra of ferroelectric-semiconductor Zn
0.8Li
0.2O single crystal have been observed as a function of temperature for several scattering geometries. The crystal orientation of the small single crystal has been determined by an angular dependence study of the peak intensity of the spectra at room temperature. Observed peak frequencies are in agreement with those of the pure ZnO wurtzite crystal. Though the shape of the Raman spectra does not change extremely near the phase transition temperature, the temperature dependence of the peak position shows a small cusp like anomaly. In the low frequency region, no new modes or mode softening were observed. These results indicate that the ferroelectric-phase transition in Zn
0.8Li
0.2O system is induced by the electronic origin rather than the ionic instability.
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Akihiko Akasaka, Shoji Masunaga
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
582-584
Published: 2001
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The absorption spectra of excitons in CsBr and CsI were observed under hydrostatic pressures. The first excitons Γ 3/2 in CsBr and CsI showed blue shifts, and their absorption intensities decreased with increasing pressure. The second exciton in CsI showed a red shift, and its intensity decreased as pressure increased. We propose that the red shift of the second exciton causes the metallization of CsI under very high pressure. It is pointed out that the metallization of CsBr may not occur under very high pressure. The pressure dependence of Γ 1/2 excitons in CsBr and CsI was observed. The pressure coefficient of the Γ 3/2 and Γ 1/2 excitons is discussed in terms of the Bohr radius.
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Atsuhiro Fujii, Takeshi Ono, Wei Yu
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
585-587
Published: 2001
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Optical absorption spectra of the direct exciton of TlCl microcrystals evaporated on thin films of organic polymer are measured at 5.0 K. The energies of the absorption bands shift to higher energy with decreasing microcrystal size. A new absorption band, which was not observed in a bulk crystal, is found in a microcrystal. The oscillator strength of the lower energy component of the doublet exciton states reduces in the weak confinement regime with decreasing microcrystal size and diminishes in the strong confinement regime. The experimental results are discussed with the quantum size effect on the electron-hole exchange interaction in an exciton.
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Takashi Teramoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
588-592
Published: 2001
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The main purpose of this paper is to make it clear that the physical value obtained along the trajectory generated by the new numerical scheme [J. Phys. Soc. Jpn.
69 (2000) 679.] satisfies the canonical distribution. On the basis of our proof, the scattering form factors are evaluated from the time evolution of the spatial pattern that fluctuates around the equilibrium lamellar pattern. Beyond critical values of temperature, the transitions from a lamellar pattern to hexagonal and isotropic patterns occur in the vicinity of the morphological transition point.
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Kazumoto Iguchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
593-597
Published: 2001
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Semiconductivity and band gap of a double strand of DNA are investigated by using the band gap formula from the tight-biding model for electrons in the double strand of DNA. The results quantitatively coincide with the recent experimental observations and predict many situations that are not yet performed by the experiments.
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Kiyohiro Takeuchi, Takahito Arai, Masayoshi Tajiri
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
598-599
Published: 2001
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Mitsuhiro Itakura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
600-601
Published: 2001
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Yuko Sawaki, Koshi Takenaka, Shunji Sugai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
602-603
Published: 2001
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Takahiro Yamamoto, Masanari Asano, Chikara Ishii
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 2 Pages
604
Published: 2001
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