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Koyo Tamura, Yusril Yusuf, Yoshiki Hidaka, Shoichi Kai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2805-2808
Published: 2001
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Soft-mode turbulence (SMT) is a recently discovered type of spatiotemporal chaos observed in the electrohydrodynamic instability (EHD) of a nematic liquid crystal with homeotropic alignment. Its novelty is that it occurs as the first supercritical bifurcation from a stable stationary state in the weakly nonlinear regime of EHD. A particle, small compared to the characteristic length of the macroscopic flow, injected in SMT travels with random velocity similar to a particle in Brownian motion. We find that the particle trajectory exhibits anomalous Brownian motion such as pumped flight and that the macroscopic diffusion constant due to weak turbulence is about 10
3 times larger than the diffusion constant associated with the rest state. The stochastic properties of SMT are discussed.
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Namiko Mitarai, Hiizu Nakanishi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2809-2812
Published: 2001
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We numerically study the stability of granular flow on a rough slope in a collisional flow regime in two dimensions. We examine the density dependence of the flow behavior in a low-density region, and demonstrate that the particle collisions stabilize the flow above a certain density in the parameter region where a single particle shows an accelerated behavior. Within this parameter regime, however, uniform flow is only metastable and is shown to be unstable against clustering when the particle density is not sufficiently high.
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Wei Sun, Takayoshi Kimoto, Takao Furubayashi, Takehiko Matsumoto, Syoz ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2813-2816
Published: 2001
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The structural phase transition in a thiospinel CuIr
2S
4 compound which is associated with a metal-to-insulator transformation at approximately 230 K was studied by
in-situ low-temperature transmission electron microscopy. It was directly revealed that the structural transition is characterized by the formation of fine {110} twin lamellae and the appearance of additional electron diffraction spots along the <100>
*, <110>
* and <111>
* directions of the room-temperature cubic CuIr
2S
4. On the basis of results of electron diffraction analysis, the lattice structure and symmetry of the CuIr
2S
4 low-temperature insulating phase were determined. Furthermore, we found that the characteristic additional diffraction spots for the insulating phase became quite faint or disappeared when the temperature decreased below approximately 50 K. This suggests a subsequent structural change in the insulating CuIr
2S
4 at extremely low temperatures.
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Wei Sun, Takayoshi Kimoto, Takao Furubayashi, Takehiko Matsumoto, Syoz ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2817-2820
Published: 2001
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The structural phase transition in a thiospinel CuIr
2S
4 compound which is associated with a metal-to-insulator transformation at approximately 230 K was studied by
in-situ low-temperature transmission electron microscopy. It was directly revealed that the structural transition is characterized by the formation of fine {110} twin lamellae and the appearance of additional electron diffraction spots along the <100>
*, <110>
* and <111>
* directions of the room-temperature cubic CuIr
2S
4. On the basis of results of electron diffraction analysis, the lattice structure and symmetry of the CuIr
2S
4 low-temperature insulating phase were determined. Furthermore, we found that the characteristic additional diffraction spots for the insulating phase became quite faint or disappeared when the temperature decreased below approximately 50 K. This suggests a subsequent structural change in the insulating CuIr
2S
4 at extremely low temperatures.
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Seiichiro Miura, Michinobu Mino, Hitoshi Yamazaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2821-2824
Published: 2001
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The relaxation of a two-dimensional labyrinth pattern of magnetic domain structure in a uniaxial garnet thin film is studied. The usually observed domains of the labyrinth structure contain many defects. The labyrinth structure changes to a parallel-stripe structure under magnetic field cycles. In this evolution, defects of the domain pattern disappear. We have introduced a number of magnetic domain junctions as characteristic values of a domain pattern. A magnetic domain junction is defined as a point where magnetic domains in the same direction intersect like a three-forked road. This is one type of defect in the domain pattern. It is found that the number of junctions decreases with the power law as a function of the number of ac magnetic field cycles.
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Ken Yokoyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2825-2828
Published: 2001
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The one-particle Green's function for the two-chain Tomonaga-Luttinger (TL) model coupled by interchain hopping including spin degrees of freedom is calculated as a function of distance and time by the higher-dimensional bosonization method. In the short distance and time region, the one-dimensional TL liquid behavior is reproduced, while the long distance and time behavior is different from that for either TL or Fermi liquid. As the interaction becomes stronger, the behavior of Green's function becomes closer to that for the one-dimensional TL liquid, showing that the one-dimensionality is enhanced for stronger electron interaction, and is interpreted as the precursor of the “confinement”.
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Shin-ichi Kimura, Mitsuru Okuno, Hideki Iwata, Hidekazu Aoki, Akira Oc ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2829-2832
Published: 2001
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To investigate the anomalous transport property and the electronic structure near the Fermi level of Yb
4As
3, we measured the temperature dependence of the reflectivity spectra of Yb
4(As
1-xP
x)
3 (x = 0, 0.05, 0.15) in the photon energy range of 2 meV-1.5 eV. The optical conductivity spectrum due to carrier absorption (Drude curve) significantly changes with temperature. Above 200 K, the Drude curve with a high effective carrier density (N
eff) and a short relaxation time (τ) is commonly observed in all Yb
4(As
1-xP
x)
3. On the other hand, below 70 K, the Drude curve changes to one with a low N
eff and a long τ below 10 meV. At the same temperature, a new peak appears at 15 meV in Yb
4As
3. The Drude curve and the new peak are considered to originate from the bare As 4p hole band and the hybridization state between the 4f and 5d bands on the Yb
3+ chain, respectively.
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Takashi Yanagisawa, Shigeru Koikegami, Hajime Shibata, Shinji Kimura, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2833-2835
Published: 2001
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Optical conductivity spectra σ
1(ω) of Nd
2-xCe
xCuO
4 thin films, measured by the reflectance-transmittance method (R-T method) which has been proposed to investigate far-infrared spectroscopy, are investigated based on the anisotropic pairing model. Precise measurements of the frequency-dependent conductivity σ
1(ω) enable us to examine quantitatively the nature of the superconducting gap through infrared properties for the first time in high-T
c superconductors. We show that the behavior of optical conductivity σ
1(ω) is consistent with the anisotropic superconducting gap and is well explained by the formula for d-wave pairing in the far-infrared region. Our results suggest that the electron-doped cuprate superconductors Nd
2-xCe
xCuO
4 have nodes in the superconducting gap.
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Daijiro Yoshioka
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2836-2839
Published: 2001
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The effect of periodic potential on the stripe phase realized at high Landau levels is investigated by the Hartree-Fock approximation. The period of the potential is chosen to be two to six times the fundamental period of the stripe phase. It is found that the stripe aligns perpendicularly to the external potential in contrast to a naive expectation and hydrodynamic theory. Charge modulation towards the Wigner crystallization along the stripe is essential for the occurrence of the present unexpected new result.
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Hiroshi Kontani
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2840-2843
Published: 2001
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We present a microscopic theory for the thermoelectric power (TEP) in high-T
c cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a two-dimensional Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-T
c cuprates, which have been a long-standing problem in high-T
c cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.
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Yasumoto Tanaka
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2844-2847
Published: 2001
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When a superconductor has multiple bands and there is a phase difference of π between Δ
1 and Δ
2 where Δ
i is a gap parameter on a band indexed by i, the junction formed with another superconductor rotates the relative phase between Δ
1 and Δ
2 near the interface to lower the Josephson coupling energy. This means that the order parameter is no longer a real number but is a complex number. This phase-instability is demonstrated with a simple model describing the two-band superconductor in terms of the Ginzburg-Landau theory. Due to this effect there is a phase shift between the two bulk superconductors forming the junction. Using a quantum interferometer we will be able to detect this shift experimentally.
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Hiroto Adachi, Ryusuke Ikeda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2848-2851
Published: 2001
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The fluctuation conductivity σ
s in bulk superconductors with non s-wave pairing and with nonmagnetic disorder of strength D is studied at low T and within the Gaussian approximation. It is shown by assuming a quasi two-dimensional (2D) electronic state that, only if the gap function d
μ(p) is, as in a 2D p-wave pairing state, linear in the in-plane (relative) momentum p
⊥, the in-plane fluctuation conductivity on the line D=D
c is weakly divergent in low T limit. The present result may be useful in clarifying the true gap function of spin-triplet Sr
2RuO
4 through resistivity measurements.
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Kouji Yasui, Takafumi Kita
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2852-2855
Published: 2001
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We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation in the vortex state of type-II superconductors, with a special focus on the connection between the gap anisotropy and the oscillation damping. Numerical calculations for three different gap structures clearly indicate that the average gap along the extremal orbit is relevant for the magnitude of the extra damping, thereby providing support for experimental efforts to probe gap anisotropy through the dHvA signal. We also derive an analytic formula for the extra damping which will be useful to estimate angle- and/or band-dependent gap amplitudes.
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Koji Yoshida, Setsuko Tajima
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2856-2859
Published: 2001
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We investigated pressure P effects on the in-plane resistivity of the Zn-substituted YBa
2Cu
3O
7-δ (Y123) with the optimal carrier doping. The increasing rate of T
c with P is larger in the Zn-substituted Y123 than in the Zn-free Y123, which implies an intriguing reduction of the pair-breaking effect. We attribute the primary origin of this pair-breaking suppression to a weakening of the impurity potential scattering with P, which was demonstrated by a decrease in the residual resistivity due to the P-induced carrier doping and a consequent change in the scattering phase shift.
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Masashige Matsumoto, Mikito Koga
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2860-2863
Published: 2001
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Orbital degrees of freedom of a Cooper pair play an important role in the unconventional superconductivity. To elucidate the orbital effect in the Kondo problem, we investigated a single magnetic impurity coupled to Cooper pairs with a p
x +ip
y (d
x2-y2+id
xy) symmetry using the numerical renormalization group method. It is found that the ground state is always a spin doublet. The analytical solution for the strong coupling limit explicitly shows that the orbital dynamics of the Cooper pair generates the spin 1/2 of the ground state.
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Shigenori Tsuji, Masafumi Sera, Kenichi Kojima
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2864-2867
Published: 2001
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We analyze the
11B-NMR spectrum for H || <001> in phase III of CeB
6 quantitatively. The experimental results are reproduced by taking the sum of the dipolar field and the transferred hyperfine field from the Ce site. Their absolute values and also the magnitude of the antiferro-magnetic moment are estimated. These results show that the O
xy AFQ ordering in phase II continues to exist also in the AF magnetic phase III.
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Atsuko Fukaya, Isao Watanabe, Kanetada Nagamine
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2868-2871
Published: 2001
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We measured muon spin relaxation for a copper borate Cu
3B
2O
6, which has a two-dimensional network of Cu
2+ spins. It was previously reported that the ground state of this compound was a spin singlet state [G. A. Petrakovskii et al.: Phys. Solid State
412 (1999) 610]. We, however, observed an oscillation of muon spins at low temperatures, which indicates that the ground state is a long-range-ordered state. A critical slowing down of the fluctuations of electronic spins is not observed near the critical temperature, ∼11 K, suggesting that the magnetic transition is not an ordinary second-order phase transition. In addition, the coexistence of paramagnetic domains and ordered domains is observed at 6 K<T<12 K.
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Masahito Mochizuki, Masatoshi Imada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2872-2875
Published: 2001
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The possibility of the D
3d distortion of TiO
6 octahedra is examined theoretically in order to understand the origin of the G-type antiferromagnetism [AFM(G)] and experimentally observed puzzling properties of LaTiO
3. By utilizing an effective spin and pseudospin Hamiltonian with the strong Coulomb repulsion, it is shown that the AFM(G) state is stabilized through the lift of the t
2g-orbital degeneracy accompanied by a tiny D
3d-distortion. The estimated spin-exchange interaction is in agreement with that obtained by the neutron-scattering experiment. Moreover, the level-splitting energy due to the distortion can be considerably larger than the spin-orbit interaction even when the distortion becomes smaller than the detectable limit under the available experimental resolution. This suggests that the orbital momentum is fully quenched and the relativistic spin-orbit interaction is not effective in this system, in agreement with the result of a recent neutron-scattering experiment.
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Naoyuki Tateiwa, Katsumi Hanazono, Tatsuo C. Kobayashi, Kiichi Amaya, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2876-2879
Published: 2001
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We performed DC-magnetization and neutron scattering experiments under pressure P for a pressure-induced superconductor UGe
2. We found that the magnetic moment is enhanced at a characteristic temperature T
* in the ferromagnetic state, where T
* is smaller than a Curie temperature T
C. This enhancement becomes remarkable in the vicinity of P
C*=1.20 GPa, where T
* becomes 0 K and the superconducting transition temperature T
SC shows a maximum. The characteristic temperature T
*, which decreases with increasing pressure, also depends on the magnetic field.
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Daiki Yanagishima, Yoshiteru Maeno
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2880-2883
Published: 2001
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We report the low temperature properties of a new series of pyrochlore iridates R
2Ir
2O
7 (R=rare-earth elements). We found that the compounds with R=Pr, Nd, Sm, and Eu exhibit metallic conductivity, whereas those with smaller rare-earth ions are nonmetallic. Such metal-nonmetal changeover is attributable to the importance of electron correlation among the Ir 5d electrons. Reflecting the geometrical frustration in the pyrochlore lattice, the rare-earth moments do not exhibit magnetic ordering to temperatures well below the antiferromagnetic Weiss temperature. We did not find any sign of superconductivity down to 0.3 K in these compounds.
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Yuh Tomio, Yoshikazu Suzumura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2884-2887
Published: 2001
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The collective modes representing density fluctuation in a spin density wave (SDW) have been examined for a one-dimensional electron system of a quarter-filled extended Hubbard model with the next-nearest-neighbor interaction (V
2). Within the random phase approximation (RPA), we obtain a new collective mode, which appears with increasing V
2. The mode describes the relative motion between density wave with up spin and that with down spin. The gap in the excitation spectrum vanishes at a critical value of V
2 corresponding to the onset of the coexistence of 2k
F-SDW, 2k
F-charge density wave and 4k
F-SDW in the ground state (k
F being the Fermi wave vector).
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Kyu Won Lee, Cheol Eui Lee, Jun-Kun Kang
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2888-2891
Published: 2001
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Proton nuclear magnetic resonance (NMR) relaxation measurements were carried out to investigate the low-frequency hydrocarbon chain dynamics in decylammonium chloride (C
10H
21NH
3Cl), a model biomembrane undergoing an irreversible structural phase transition. It is demonstrated by systematic proton NMR study of spin-spin relaxation and rotating frame spin-lattice relaxation that a low-frequency chain dynamics is responsible for the critical dynamics associated only with the interdigitated-to-noninterdigitated chain configurational phase transition.
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Tatsuya Nagao, Jun-ichi Igarashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2892-2895
Published: 2001
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We theoretically investigate the origin of the resonant X-ray scattering (RXS) signal near the Ce L
III absorption edge in the quadrupolar ordering phase of CeB
6, considering the intersite interaction between the Γ
8 states in the initial state. The anisotropic charge distribution of the 4f states modulates the 5d states through the intra-atomic Coulomb interaction and thereby generates a large RXS superlattice intensity. The temperature and magnetic field dependence indicates that the induced dipolar and octupolar orders have little influence on the RXS spectra, in good agreement with the recent experimental results.
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Katsumi Hagita, Daisuke Ishizuka, Hiroshi Takano
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2897-2902
Published: 2001
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Relaxation of a single polymer chain trapped in a periodic array of obstacles in two dimensions is studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account. Relaxation modes and rates of the polymer chain are estimated by solving a generalized eigenvalue problem for the equilibrium time correlation matrices of the coarse-grained relative positions of segments of the polymer chain. The slowest relaxation rate λ
1 of the polymer chain of N segments behaves as λ
1 ∝ N
-3.1. The pth slowest relaxation rate λ
p with p ≥ 2 shows the p-dependence λ
p ∝ p
2.1 and the N-dependence consistent with λ
p ∝ N
-3.1 for small values of p/N. For each N, the slowest relaxation rate λ
1 is remarkably smaller than the value extrapolated from the behavior λ
p ∝ p
2.1 for p ≥ 2. The behaviors of slow relaxation modes are similar to those of the Rouse modes. These behaviors of the relaxation rates and modes correspond to those of the slithering snake model with the excluded volume interaction.
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Avinash Agarwal, M. K. Bhardwaj, I. A. Rizvi, A. K. Chaubey
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2903-2908
Published: 2001
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Excitation functions of the reactions (α, 2n), (α, 3n), and (α, 4n) for
103Rh have been measured with stacked foil activation technique for the projectile energies below 50 MeV α-particles. A large volume HPGe detector was used. The experimental data were compared with the calculated values obtained from the CASCADE code based on statistical model and ALICE-91 code based on Hybrid and Geometry Dependent Hybrid Models. It is found that the pre-equilibrium contribution is more pronounced in the high energy region of the excitation functions and the experimental data are explained only when the pre-equilibrium emission phenomenon is also taken into account along with the equilibrium decay. The percentage of pre-equilibrium fraction has also been calculated.
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Ho-Young Kwak, Joong-Yeob Lee, Sarng Woo Karng
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2909-2917
Published: 2001
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Problems involved in the bubble dynamics models which have been suggested to explain the sonoluminesence phenomena from a single bubble under ultrasound were discussed. One of the problems is proper choice of the time scale of the driving force, which is related to numerical artifacts due to the mismatch between the natural frequency of an oscillator (bubble) and the characteristic frequency of the applied force. Such problem may occur in a nonlinear oscillator whose behavior is crucially dependent on the frequency of the applied force. The characteristics of bubble behavior for the sonoluminescing gas bubble and the artificial resonance problem encountered during the numerical evaluation of such nonlinear system were also discussed.
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Masashi Torikai, Komajiro Niizeki, Takashi Odagaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2918-2933
Published: 2001
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Self-similar binary one-dimensional (1D) quasilattices (QLs) are classified into mutual local-derivability (MLD) classes. It is shown that the MLD classification is closely related to the number-theoretical classification of parameters which specify the self-similar binary 1D QLs. An algorithm to derive an explicit substitution rule, which prescribes the transformation of a QL into another QL in the same MLD class, is presented. An explicit inflation rule, which prescribes the transformation of the self-similar 1D QL into itself, is obtained as a composition of the explicit substitution rules. Symmetric substitution rules and symmetric inflation rules are extensively discussed.
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Yasumitsu Matsuo, Keisuke Takahashi, Seiichiro Ikehata
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2934-2938
Published: 2001
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We have studied the proton motion below the ferroelastic-paraelastic phase transition (superionic transition) temperature T
c=449 K from the NMR absorption lines. From the analysis of the NMR absorption lines, it was found that the second moment changes drastically in the temperature region from 340 K to 420 K. Moreover, we obtained the result that even below T
c the correlation time of proton τ
c obeys the Arrhenius relation τ
c = τ
0 exp(Δ E / kT) with τ
0=4.3 × 10
-11 s and Δ E= 0.47 eV. This activation energy is close to that of proton above T
c. Furthermore, the electric conductivity calculated with τ
c, which is obtained from the second moment of the NMR absorption lines, was compared with the experimental one. The result indicated that proton motion plays an important role in the electric conductivity even below T
c.
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Yoshihisa Enomoto, Katsumi Oba, Yumino Hayase, Takao Ohta
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2939-2947
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In a previous paper [M. Matsushita and T. Ohta: J. Phys. Soc. Jpn.
67 (1998) 1973], the model equation for a structural phase transition between a hexagonal symmetry and a square symmetry has been introduced and numerical simulations have been carried in two dimensions where the order parameter is a non-conserved quantity. In the present paper, we extend the model equation for the conserved order parameter. The thermal random force is also taken into account. The kinetics of the structural transition is studied by analyzing the non-equilibrium scattering function of the domain structures and by evaluating the time-dependence of the volume fraction of one of the structures. The equilibrium phase diagram for domain structures is also derived by means of the single wave number approximation.
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Fujio Kakinuma, Yoshimi Tsuchiya
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2948-2952
Published: 2001
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Sound velocity and molar volume have been measured in the liquid Ag-Te system as a function of temperature and composition. Results obtained have been used to deduce the compressibility and thermal expansion coefficient. The molar volume and adiabatic compressibility show a distinct cusp at Ag
2Te composition where the thermal expansion coefficient takes a minimum, which suggests the existence of stable ionic association in the liquid. Between Ag and Ag
2Te the adiabatic compressibility for an alloy with a miscibility gap shows a logarithmic temperature dependence being characteristic of the critical behaviour associated with the two-melt phase separation. A very small two-melt region has been confirmed. Discussion has been made in comparison with the results for the isochemical system, Ag-Se.
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Shijin Zhao, Shaoqing Wang, Hengqiang Ye
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2953-2957
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The melting properties of free nanoclusters of silver atoms interacting through an analytic embedded-atom method type potential are studied by using molecular dynamics simulations. The particle-size-dependent depression of the melting temperature T
m of Ag
258-3871 can be explained by the surface premelting models (SPM). The melting process of Ag
13-178 changes significantly compare with that of Ag
258-3871, in which T
m deviate from the values predicted from the SPM and the latent heat of fusion Δ u
ls enhance greatly. For the first time, the size-dependent variations in T
m and Δ u
ls for free neutral nanoclusters with r≤slant r
c (r
c is critical radius) is presented and a new intermediate melting mechanism is identified. In addition, a reentrant morphology transition in Ag
147, quasimelten phases of Ag
13-55, and icosahedral precursors to the melting of Ag
13-309 are also recovered.
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Katsukuni Yonashiro, Masahiko Iha
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2958-2960
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The dependence of the ionic conductivity on the mobile ion concentration in superionic conductors is studied by making use of the lattice gas model with a hopping term and Kubo's formula. The ionic conductivity has symmetry with respect to concentration ρ=1/2, and has a minimum value at ρ=1/2 and a maximum value at ρ ≈ 0.3 and ρ ≈ 0.7. The ionic conductivity first increases with the increasing mobile ions, and has the maximum and then decreases with the further increase of mobile ion concentration by increasing the repulsive interaction among the mobile ions. At 50% concentration, it is understood that the ionic conductivity has the minimum because the mobile ion and the vacancy occupy the lattice sites alternatively.
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Sheng-Feng Cheng, Guo-Jun Jin, Ru-Wen Peng, An Hu
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2961-2967
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We study the coupled optical interface modes in a Thue-Morse dielectric superlattice. Based on the electrostatic continuum approximation, which is correct in the long wavelength limit, the transfer matrix method is used to derive the analytic expressions for frequency spectra and electrostatic potential distributions. The numerical calculations show that the frequency spectra are
singular continuous, and the potential profiles are mostly
extended and
lattice-
like. The common features and pronounced differences with coupled optical interface modes in periodic and Fibonacci dielectric superlattices as well as with electrons and acoustic phonons in Thue-Morse structures are exposed. Furthermore, the possibility of experimental observation is discussed.
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Norio Miyasaka, Yoshiyuki Ono
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2968-2976
Published: 2001
Released on J-STAGE: February 28, 2003
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The static and dynamical properties of an acoustic polaron in a two-dimensional electron-lattice system is studied numerically on the basis of Su, Schrieffer and Heeger's Hamiltonian (SSH Hamiltonian) extended to two dimensions. As for the static structure of the polaron, the coupling constant dependence of the width is analyzed. It is confirmed that, in contrast to the one-dimensional case, the two-dimensional acoustic polaron is stable only when the dimensionless electron-lattice coupling constant exceeds a certain critical value. As the coupling constant is reduced from a larger value, the polaron width increases, but the polaron becomes unstable before the width diverges. The dynamics of the polaron is studied by applying an external electric field which accelerate the polaron in a natural way. Similarly to the one-dimensional system the polaron velocity shows a saturation, though the saturation velocity is about one quarter of that in the one-dimensional case which is known to be nearly equal to the sound velocity of the system. From the relation between the velocity and the energy of the polaron the effective mass is estimated.
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Tsuneaki Miyahara, Hiroyoshi Ishii, Yasuhiro Takayama, Masaaki Hirose, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2977-2981
Published: 2001
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Core excited magnetic circular dichroism (MCD) signals have been measured on PrFe
4P
12 and CePd
3 under the states without magnetic order. The inverse values of the MCD magnitudes have been plotted against temperatures to be compared with the inverse plots of the bulk susceptibility. It has been found on PrFe
4P
12 that the inverse of MCD magnitudes behaves like a material with local magnetic moments at high temperature region but behaves as if the local magnetic moments disappear at low temperature region with T
K much higher than 10 K, while its bulk susceptibility is known to show a “ferromagnetic” behavior above 6 K. Those on CePd
3 have been found to behave like a normal dilute Kondo alloy as if T
K is around 20 K, which contradicts the known T
K of 150 K and is in striking contrast to our former result on CeFe
4P
12. This result suggests that T
K of a “coherent” Kondo material could be much higher than T
K observed through “local” spin fluctuation due to some antiferromagnetic interaction between neighboring 4f moments.
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Yoshihumi Tokiwa, Takahiro Maehira, Shugo Ikeda, Yoshinori Haga, Etuji ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2982-2988
Published: 2001
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We succeeded in growing a high-quality single crystal of UFeGa
5 by the self-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and de Haas-van Alphen (dHvA) oscillation. Many dHvA branches were observed, ranging from 5.4×10
5 to 1.4× 10
8 Oe. These branches are in good agreement with theoretical ones based on 5f-itinerant RLAPW band calculations. The cyclotron mass is relatively large, ranging from 2.4 to 9.9 m
0.
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Yasuo Ohashi, Yoshiaki Ono
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2989-2998
Published: 2001
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The Mott metal-insulator transition in the two-band Hubbard model in infinite dimensions is studied by using the linearized dynamical mean-field theory. The discontinuity in the chemical potential for the change from hole to electron doping is calculated analytically as a function of the on-site Coulomb interaction U at the d-orbital and the charge-transfer energy Δ between the d- and p-orbitals. Critical behaviour of the quasiparticle weight is also obtained analytically as a function of U and Δ. The analytic results are in good agreement with the numerical results of the exact diagonalization method.
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Keisuke Oda, Shunsuke Yoshii, Yukio Yasui, Masafumi Ito, Takahiko Ido, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
2999-3005
Published: 2001
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Hall resistivities ρ
H, the magnetizations M and the magnetoresistances Δρ have been measured as functions of the applied magnetic field H in the wide temperature range for ferromagnetic systems of CuCr
2S
4, Cu
0.5Zn
0.5Cr
2Se
4 and Cr
3Te
4, which are considered to have non-trivial spin structures below the temperature T
m. For CuCr
2S
4 and Cr
3Te
4, the Hall resistivities have been found to deviate from the ordinary expression ρ
H=R
0H+4π R
sM below T
m, where R
0 and R
s are the ordinary and anomalous Hall coefficients, respectively. The sign change of R
s with T has also been observed for all the systems. These behaviors are discussed in relation to their possibly non-trivial magnetic structures.
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Taketomo Kageyama, Satoshi Iikubo, Shunsuke Yoshii, Yasuyuki Kondo, Ma ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3006-3010
Published: 2001
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Hall resistivity ρ
H has been studied for single crystals of Nd
2Mo
2O
7, which has the ferromagnetic and chiral ordered state. Effects of Ti-doping on ρ
H have also been studied down to 3 K under the magnetic field (H) up to 7 T. The T- and H-regions of the measurements have been extended for non-doped samples to 50 mK and 15 T, respectively. From the results, it has been confirmed that two components of the anomalous Hall resistivity exist. One is proportional to the net magnetization of Mo atoms, M
Mo. It changes its sign with the doping. The other is proportional to the net magnetization of Nd atoms, M
Nd and does not exhibit the sign change. The Hall resistivity has a finite and almost T-independent value at very low temperatures. These results on the behavior of ρ
H are discussed by considering the existing theories including the one recently proposed by a mechanism related to the spin chiral order.
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Hirono Fukazawa, Takuji Nomura, Hiroaki Ikeda, Kosaku Yamada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3011-3017
Published: 2001
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The borocarbide YNi
2B
2C with quasi-2-dimensional structure encounters a superconducting transition at T
c= 15.4 K, the pairing symmetry of which is not clarified; most of experiments suggest an extended s-wave state, while some claim a d-wave. In this paper, we investigate a possibility of a d-wave state, solving the Éliashberg equation within the third order perturbation theory for a repulsive Hubbard model with the band structure reproducing the main Fermi surface. It is shown that if the electron correlation gives the dominant contribution to the superconducting pairing interaction, the d
xy-symmetry is the most favorable state corresponding to the (π, 0) peak structure of the spin susceptibility.
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Atsushi Suzuki, Masanori Taira, Morio Suzuki, Xu-Guang Zheng
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3018-3022
Published: 2001
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The tunneling measurement was carried out for the planar junctions fabricated on Bi
2Sr
2CaCu
2O
8-x (BSCCO) at a temperature ranging from 4.2 K to 100 K. The tunnel conductance spectrum, G(V) at low temperature showed a clear superconducting gap structure for a single crystal of BSCCO with a (001) face and a clear Andreev reflection structure for a ceramic one. Both structures weakened with increasing temperature and disappeared at the critical temperature T
c. The temperature dependence of these structures was found to agree with the theoretical prediction due to the Andreev reflection in a d-wave superconductor. From the simulation of the normalized conductance g(V), the g(V) characteristic was found to be almost independence of the spread of wave space which was probed by the one electron tunneling.
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Ryusuke Kondo, Tatsuo Hasegawa, Tomoyuki Mochida, Seiichi Kagoshima, Y ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3023-3030
Published: 2001
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Low-temperature electronic properties of the first all-organic donor-acceptor-type superconducting system, (BETS)
2(X
2TCNQ) [X=Cl, Br] under high pressure have been investigated by means of resistivity and
1H NMR experiments. The crystal structure of this class of complexes is characterized by a twin-columnar structure of BETS without intra-columnar dimerization at room temperature. Pressure-temperature phase diagrams are established for these compounds, where the electronic ground states are spin-density-wave (SDW's) insulators, except a narrow region of superconducting state in (BETS)
2(Cl
2TCNQ). A possible unified picture of the electronic states of the title compounds is discussed in terms of hydrostatic pressure effects and chemical substitution ones on them.
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Yasuaki Oohara, Mamoru Mekata, Tsuyoshi Morishita, Kazuhisa Kakurai, M ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3031-3036
Published: 2001
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Magnetic ordering of CuFe
0.95Al
0.05O
2 was studied by neutron scattering. CuFe
0.95Al
0.05O
2 exhibits a quasi-long-range order below a pseudo-Néel temperature, T
N=13.5 K. The magnetic structure is a helical structure with the propagation vector (0.196 0.196 3/2). However, a true long-range order is not established even at 1.7 K. Neutron spin-echo measurements revealed that the ordered magnetic moment becomes static below T
N. The existence of the helical structure suggests that an Ising anisotropy of CuFeO
2 is weak.
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Jae-Hyuk Choi, Hyeonjin Doh, Eun-Mi Choi, Heon-Jung Kim, Sung-Ik Lee, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3037-3041
Published: 2001
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We have investigated the low-temperature specific heat of HoNi
2B
2C down to T = 1 K in various magnetic fields from 0 T to 5 T. At zero field, the specific heat exhibits a large peak at T
N = 5.1 K, which is due to commensurate antiferromagnetic ordering, and other smaller peak at T
1 = 5.5 K, which is related to incommensurate ordering. As the field is increased up to 0.5 T, the first peak broadens and moves to a lower temperature, while the other peak at T
1 moves to a higher temperature, which indicates that the phase between T
N and T
1 is more favored in magnetic fields. Among possible candidates for the phase, the a-axis modulation phase, which is an extension of a low temperature metamagnetic state, is the most probable. In the high-field region above 1 T, the two-peak feature is replaced by a broad-hill one that fades away with increasing fields, which is the typical smearing feature of the magnetic order at high fields.
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Hideki Abe, Kenji Yoshii, Hideaki Kitazawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3042-3045
Published: 2001
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The magnetic properties of an intermetallic compound ErTi
2Ga
4 with the tetragonal (I4/mmm) structure was investigated. The magnetic measurements on the poly- and single crystalline specimens have shown that the compound is a ferromagnet with T
c of 10 K and the ordered magnetic moment (μ=9 μ
B/f.u.) parallel to the a-axis. It was found also that the magnetic isotherms of polycrystalline ErTi
2Ga
4 do not obey the Arrot's relationship (linearity between M
2 and H/M), which suggests that the coupling of the moment fluctuation is quite weak in this system.
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Takuo Sakon, Takashi Namiki, Mitsuhiro Motokawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3046-3051
Published: 2001
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Isothermal magnetization processes of a Uranium compound UPd
2Al
3 is first studied at temperatures down to 40 mK in static magnetic fields up to 20 T using a superconducting magnet and a hybrid magnet with a `Capacitance Method' type magnetometer newly developed by ourselves. A sharp metamagnetic transition is shown around 18 T for Ballel basal plane of hexagonal structure. Moreover, a hysteresis have been first observed below 4.2 K. The hysteresis becomes larger with decreasing temperature and is as large as about 0.02 T at 40 mK. This hysteresis and sharp transition of the magnetization suggest that this transition is of the first order. The transition field becomes higher with lowering temperature.
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Tsuyoshi Kashima, Masatoshi Imada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3052-3067
Published: 2001
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Numerical studies on Mott transitions caused by the control of the ratio between bandwidth and electron-electron interaction (U) are reported. By using the recently proposed path-integral renormalization group (PIRG) algorithm, physical properties near the transitions in the ground state of two-dimensional half-filled models with the nearest and the next-nearest neighbor transfers (-t and t
′, respectively) are studied as a prototype of geometrically frustrated system. The nature of the bandwidth-control transitions shows sharp contrast with that of the filling-control transitions: First, the metal-insulator and magnetic transitions are separated each other and the metal-insulator (MI) transition occurs at smaller U, although the both transition interactions U increase with increasing t
′. Both transitions do not contradict the first-order transitions for smaller t
′/t while the MI transitions become continuous type accompanied by emergence of
unusual metallic phase near the transition for large t
′/t. A nonmagnetic insulator phase is stabilized between MI and AF transitions. The region of the nonmagnetic insulator becomes wider with increasing t
′/t. The phase diagram naturally connects two qualitatively different limits, namely the Hartree-Fock results at small t
′/t and speculations in the strong coupling Heisenberg limit.
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Yosuke Tanaka, Hidekazu Tanaka, Toshio Ono, Akira Oosawa, Kiyoko Moris ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3068-3075
Published: 2001
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The ground state of the stacked triangular antiferromagnet CsFeBr
3 is a spin singlet due to the large single ion anisotropy D(S
z)
2. The field-induced magnetic ordering in this compound was investigated by the magnetic susceptibility, the magnetization process and specific heat measurements for an external field parallel to the c-axis. Unexpectedly, two phase transitions were observed in the magnetic field H higher than 3 T. The phase diagram for temperature vs. magnetic field was obtained. The mechanism leading to the successive phase transitions is discussed.
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Hiroaki Kusunose, Yoshio Kuramoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3076-3083
Published: 2001
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Elementary excitations in the multipole ordered state, which models the phase III in CeB
6, are investigated by means of a generalized Holstein-Primakoff formalism. When different kinds of nearest-neighbor exchange interactions between multipoles are comparable to each other, orbital-flip excitations exhibit almost one-dimensional dispersion along the k
z axis. With high symmetry of the interactions, zero modes appear due to the macroscopic degeneracy of the ground state. The next-nearest-neighbor Γ
4u2-type interaction, which stabilizes the magnetic order of the phase III in CeB
6, lifts the degeneracy and leads to gapfull excitation spectrum. When the next-nearest-neighbor Γ
5u-type interaction exists simultaneously, the spectrum shows softening at Γ and Z points. These excitations may be probed by neutron scattering and ultrasonic measurements.
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Miki Ueda, Satoru Maegawa, Hitoshi Miyasaka, Susumu Kitagawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 10 Pages
3084-3088
Published: 2001
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We have measured the temperature, magnetic field and angular dependences of the magnetization of a single crystal of a molecular mesoscopic magnet [(C
6H
15N
3)
6Fe
8O
2(OH)
12]Br
7(H
2O)Br·8H
2O, Fe8. The molecule Fe8 consists of eight Fe
3+ ions with spins of s=5/2. The experimental results of the magnetizations at low temperatures show large anisotropy that is dependent on the orientation of the external magnetic field with respect to the crystal axis. These results are well explained by the Hamiltonian for an isolated molecule with total spin S=10 and anisotropies of D=-0.276 K and E=-0.035 K. The easy axis is determined to be oriented with an azimuthal angle of 16
º from the a-axis in the ab-plane and an inclinational angle of 0.7
º from the ab-plane.
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