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Shinobu Aoyagi, Yoshihiro Kuroiwa, Akikatsu Sawada, Hiroshi Tanaka, Ji ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2353-2356
Published: 2002
Released on J-STAGE: April 25, 2003
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In cubic PbZrO
3, which undergoes an antiferroelectric phase transition, the distinct disorder of Pb at twelve sites toward the neighboring O is detected for the first time by analyzing high-energy X-ray powder diffraction data. In the charge density distributions, the covalent nature of the Pb-O bond is also revealed, which proves the existence of electron hybridization between O and disordered Pb in cubic PbZrO
3. None of these structural characteristics of PbZrO
3 were found in the previously studied cubic PbTiO
3 structure [Y. Kuroiwa
et al.: Phys. Rev. Lett.
87 (2001) 217601], which undergoes a ferroelectric phase transition. This may be a clue to understanding why PbTiO
3 and PbZrO
3 respectively show ferroelectric and antiferroelectric phase transitions.
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Shuji Ishihara, Kunihiko Kaneko
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2357-2360
Published: 2002
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A lattice dynamics model exhibiting history dependence is proposed, inspired by recent sandpile experiments. The stress distribution depends on the preparation process, which is explained as the dependence of certain attractors on the preparation conditions of the system. The model has three phases, but the history dependence is shown to exist only in the phase where a perturbation is amplified selectively rather than globally when propagating in the downflow direction. The condition for this history dependence is given in terms of the spatial Lyapunov exponent.
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Wataru Higemoto, Akihiro Koda, Goro Maruta, Kusuo Nishiyama, Hiroyuki ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2361-2364
Published: 2002
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We performed muon spin relaxation (μSR) experiments on a S =1/2 triangular lattice system, BaVS
3. Fast muon spin relaxation was observed below T
X ∼eq 30 K, indicating magnetic ordering. The hyperfine field at the muon site is about 500 G at 2.2 K, which agrees with the spin structure proposed from recent low-energy neutron diffraction results. No fast fluctuation of local fields was observed below T
X, which restricts the interpretation of nuclear resonance data.
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Masafumi Udagawa, Masao Ogata, Zenji Hiroi
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2365-2368
Published: 2002
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Ground-state entropy for an Ising pyrochlore lattice is calculated exactly under a certain range of magnetic field along the [111] axis, where the ground-state entropy shows a plateau. The obtained entropy is 0.0808k
B per spin, which agrees with the experimental value. Pauling's method for estimating the ground-state entropy for the ice problem is also applied to the present case. Comparison of the result obtained with our exact result shows that Pauling's method underestimates the entropy by about 10%.
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Masahiro Saitoh, Noriko Okada, Eiji Nishibori, Hiroyuki Takagiwa, Tets ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2369-2372
Published: 2002
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Here, we present, for the first time, the spin density distribution of CeB
6, isostructural with CaB
6, deduced by the maximum entropy method (MEM) using polarized neutron diffraction (PND) data. Surprisingly, it reveals the presence of significant amounts of localized spin moment at non atomic sites between the nearest-neighbor boron atoms and the center of the triangle surface in the B
6 octahedron network, in addition to the negative spin moment in the center of the B
6 octahedron.
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Osamu Oishi, Seiichi Miyajima
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2373-2375
Published: 2002
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Pulsed-field-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR), combined with a quadrupole-coil rotation, was applied to the study of anisotropic self-diffusion in the smectic A phase of an antiferroelectric chiral liquid crystal MHPOBC. It was shown that diffusion within the smectic layer was significantly faster than that across the layers. The activation energies, E
a, are also significantly different: E
a for the in-layer diffusion was 30 kJ mol
-1, and that for the interlayer diffusion was 93 kJ mol
-1.
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Chishiro Michioka, Kazuya Suzuki, Ko Mibu
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2376-2379
Published: 2002
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We applied
57Fe Mössbauer spectroscopy for investigating the Ising spin triangular lattice antiferromagnet (TLA) (CeS)
1.16[Fe
0.33(NbS
2)
2] between 2 and 300 K. The spectra revealed that the relaxation time of the hyperfine field markedly changes in the intermediate phase between T
N1=22 K and T
N2=15 K due to strong spin fluctuation. The relaxation of the hyperfine field is not sufficiently fast as a paramagnet even at 77 K, which is much higher than T
N1, and the inverse susceptibility of (LaS)
1.14[Fe
0.33(NbS
2)
2] deviates from the Curie-Weiss law below 100 K. These results indicate that an unusual short-range order exists above T
N1. The temperature dependence of the Mössbauer spectra can be explained by phase transition of the three-dimensional TLA model with weak interlayer exchange interactions.
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Takeshi Ogasawara, Katsuhiro Tobe, Tsuyoshi Kimura, Hiroshi Okamoto, Y ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2380-2383
Published: 2002
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Dynamics of charge/orbital order has been investigated for Nd
0.5Ca
0.5MnO
3 with femtosecond pump-probe spectroscopy. Photo-induced changes in polarized reflectance spectra and their temporal behavior were measured for the detwinned single crystal. Marked shrinkage of charge gap as well as decrease in optical anisotropy due to partial melting of charge/orbital order is observed upon photo-excitation. Melting of charge/orbital order occurs at first within the excitation pulse duration, and then followed by relaxation of the lattice system via thermal contact with electron system with the relaxation time of approximately 1 ps.
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Suryadi, Yutaka Kadoya, Kenichi Watatani, Homare Takeda, Masamichi Ya ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2384-2388
Published: 2002
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Beat structures in the time-integrated four-wave mixing signals in semiconductor microcavities under a static electric field were investigated experimentally. We observed a significant change in the phase of the oscillation in the upper polariton mode with the change of the electric field. Through comparison with results of a theoretical analysis based on modified optical Bloch equations, the experimental results were found to strongly suggest that the exciton-exciton interaction, represented by the electric field renormalization, is significantly modified by the static electric field.
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Kazuaki Nakayama
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2389-2395
Published: 2002
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Interface dynamics coupled to the fluid particle density on the interface depends on the tangential motion of the particles. We present a generic level set equation that describes such dynamics which the standard level set technique cannot handle well.
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Yoshihiro Hirata, Kenji Imai
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2396-2400
Published: 2002
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We study Lie symmetries in general systems of ordinary differential equations and give a necessary condition for existence of Lie symmetries. With the help of our results, it is proved that several systems do not possess any analytic Lie symmetries.
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Kazuaki Narita
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2401-2405
Published: 2002
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We present the coupled discrete KdV equations, and using an extended Hirota's method developed by Chow and Lai [J. Phys. Soc. Jpn.
67 (1998) 3721], present their 1-, 2- and 3-soliton solutions under nonvanishing boundary conditions at infinity.
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Hayaru Shouno, Koji Wada, Masato Okada
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2406-2413
Published: 2002
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We attempt image restoration in the framework of the Bayesian inference. Recently, it has been shown that under a certain criterion the MAP (Maximum A Posterior) estimate, which corresponds to the minimization of energy, can be outperformed by the MPM (Maximizer of the Posterior Marginals) estimate, which is equivalent to a finite-temperature decoding method. Since a lot of computational time is needed for the MPM estimate to calculate the thermal averages, the mean field method, which is a deterministic algorithm, is often utilized to avoid this difficulty. We present a statistical-mechanical analysis of naive mean field approximation in the framework of image restoration. We compare our theoretical results with those of computer simulation, and investigate the potential of naive mean field approximation.
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Yoko Suzuki, Yoshitaka Tanimura
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2414-2426
Published: 2002
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We study an absorption spectrum of a two-dimensional rotator coupled to a colored harmonic-oscillator bath. The absorption spectrum is analytically calculated from the generating functional of a reduced density matrix element for the rotator degrees of freedom. In the previous letter [J. Phys. Soc. Jpn.
70 (2001) 1167], the analysis of spectrum is limited to a white noise case. In this paper, we extend our theory to a colored noise case. We present the spectra for different temperatures, damping strength, and the correlation time of the noise. For a weakly damped rotator, at low temperatures, the spectra are sensitive to the system dynamics that is determined by the quantization of the rotational motion. Such a quantized rotational motion depends on the noise effects. Hence we observe the peak shifts by the noise correlation time. For a strongly damped rotator, we find the bimodal spectrum in the slow modulation case. One of the peaks is caused by the effect of the colored noise, which dose not appear in the case of the white noise. This peak is related to a librational motion induced by the coupling between the system and the bath oscillators with the near zero frequencies.
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Manabu Machida, Keiji Saito, Seiji Miyashita
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2427-2433
Published: 2002
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We study the quantum localization phenomena for a random matrix model belonging to the Gaussian orthogonal ensemble (GOE). An oscillating external field is applied on the system. After the transient time evolution, energy is saturated to various values depending on the frequencies. We investigate the frequency dependence of the saturated energy. This dependence cannot be explained by a naive picture of successive independent Landau-Zener transitions at avoided level crossing points. The effect of quantum interference is essential. We define the number of Floquet states which have large overlap with the initial state, and calculate its frequency dependence. The number of Floquet states shows approximately linear dependence on the frequency, when the frequency is small. Comparing the localization length in Floquet states and that in energy states from the viewpoint of the Anderson localization, we conclude that the Landau-Zener picture works for the local transition processes between levels.
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Sunita Gupta, B. P. Singh, M. M. Musthafa, H. D. Bhardwaj, Manoj Kumar ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2434-2438
Published: 2002
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The experiment has been performed with a view to studying complete and incomplete fusion in
14N+
163D
y system below 7 MeV/nucleon. The excitation functions for several reactions have been measured using the activation technique and compared with the theoretical predictions based on statistical models. The codes ALICE-91 and CASCADE used earlier for the analysis of excitation functions in case of
12C+
165H
o system have been used here also with the same set of input parameters. It has been observed that the theoretical calculations do not match with the experimental excitation functions well but the overall shape of the excitation function is reproduced satisfactorily. The composite nucleus (
177T
a) formed in this (
14N+
163D
y) case is the same as the one formed in
12C+
165H
o system studied earlier. Measured excitation functions for the same decay channels in the two cases (i.e.
12C+
165H
o and
14N+
163D
y) have been compared. A comparison of these excitation functions indicates relatively smaller values of cross sections for all reactions in
14N+
163D
y, in general. Moreover, it has been found that in contrast to the
12C induced reactions, where a substantial part of the reaction cross section goes through incomplete fusion, there is no contribution from incomplete fusion to the reaction cross section in the case of
14N induced reactions at these energies. This may indicate that
12C undergoes breakup into
4H
e and
8B
e while
14N does not undergo breakup below 7 MeV/nucleon.
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Yuji Takamoto, Yoshio Saito, Katsuoki Kawanishi
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2439-2444
Published: 2002
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Thermal convection in a vertical cylinder in the transient cool-down process of water is investigated experimentally with three different types of bottom; (a) a conical bottom, (b) a flat one, (c) a semi-spherical one. The water is kept to be quiescent and isothermal at a temperature about 10
ºC initially, and cooled down through its maximum-density temperature. We visualize a natural convection in the cylinder by Indian ink. During the early stage of cooling, the thermal boundary layer with downward flow is formed along the wall of the cylinder. After the water temperature near the bottom falls below 4
ºC, a tiny convection with upward flow along the wall appears and grows up in time. It is observed that a bicellular convection is not uniform but wavy in the circumferential direction independently of the bottom shapes.
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Yasushi Matsunaga, Tadatsugu Hatori, Tomokazu Kato
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2445-2455
Published: 2002
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A charge exchange model is set and its simulation results are compared to those of previous friction model in the lower current branch of a discharge plasma. A remarkable delocalization of a high frequency mode is found in the charge exchange model. When the mean free path of the charge exchange is larger than the system size, the effective temperature is lower than that of the friction model. However, with a decrease of the mean free path, the temperatures of the two models are inverted. Although the bifurcations of the fundamental mode described in previous paper are similarly reproduced, a parameter range has shifted and it is difficult to observe the ponderomotive effect in the charge exchange model. Simulation results are discussed from the view point of the second moments of the distribution function in both velocity and coordinate spaces. It is found that the effects due to the ponderomotive force and previously pointed-out sheath condition are concealed under the diffusion defined by the second moment of the displacement of scattered particles.
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Dilip Kumar Saha, Toetsu Shishido, Ken-ichi Ohshima
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2456-2458
Published: 2002
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The X-ray diffuse scattering intensities were measured at room temperature for the Pt rich Pt-15.0 at.% Cr single crystal quenched from 800°C three-dimensionally. The atomic short-range order (ASRO) intensity component from the total diffuse ones was separated with the use of Borie-Sparks method [Acta Cryst. A
27 (1971) 198]. The ASRO intensity maxima were observed at the 100, 110 and their equivalent positions (X-point) on the reciprocal lattice plane, which are widely diffused. We did not find any ASRO diffuse scattering intensity at 1/2 1/2 1/2 and its equivalent positions (L-point) for the alloy. The diffuse maxima at the X-point are due to the Cu
3Au type ASRO in the present alloy case. The ASRO parameters were determined from the data and the required number of ASRO parameters, to reconstruct the peaks, indicates that the maxima are widely diffused. The correlation length is deduced to be about 10 A. Any superlattice reflections were not found from the specimen, which was annealed below 400°C for long time.
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Timbangen Sembiring, Miwako Takahashi, Keishin Ota, Toetsu Shishido, K ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2459-2465
Published: 2002
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We have performed the X-ray and electron diffraction studies to reconstruct a partial phase diagram of Pt-rich Pt-Mn alloys in the composition range of 10 to 35 at.% Mn. Electrical resistivity measurement was also used for determining the order-disorder transition temperature in Pt-14.2 at.% Mn alloy. The phase boundary between Cu
3Au type and ABC
6 type ordered structures is established, in which the latter has been found recently by the present authors [J. Phys. Soc. Jpn.
71 (2002) 681]. In the ABC
6 type ordered phase, superlattice reflections both at 1/2 1/2 1/2 and its equivalent position (L-point) and at 100, 110 and their equivalent positions (X-point) appear in the composition range from 12.5 to 14.4 at.% Mn below 682°C. In the Cu
3Au type ordered phase, diffuse maxima at L-point appear in the composition range from 15.9 to 19.7 at.% Mn in addition to the superlattice reflections at X-point. The Cu
3Au type ordered structure is found to be stable in the composition range from 19.7 to 35 at.% Mn without appearing any diffuse scattering at L-point. Furthermore, the phase boundary between Cu
3Au type and disordered state is also established.
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Kozo Hoshino
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2466-2470
Published: 2002
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The dynamical structure factors of the liquid Ge are calculated theoretically and compared with the recent experimental results obtained by the inelastic X-ray scattering. The calculation is carried out by the simple purely theoretical method, i.e. by the viscoelastic theory, which is based on the effective pair potential obtained by the pseudopotential perturbation theory and the static structure factor calculated by the integral-equation theory in the modified hypernetted-chain (MHNC) approximation. It is shown that the calculated dynamical structure factors are in qualitative agreement with the experimental results and that the calculated dispersion relation agrees well with the experimental one.
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Kenichi Oikawa, Takashi Kamiyama, Takashi Mochiku, Hiroyuki Takeya, Ma ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2471-2476
Published: 2002
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The crystal structure of a new superconducting material, MgB
2, was studied by high-resolution neutron powder diffraction as a function of temperature from 8 K to 305 K. Two samples of Mg
11B
2 were measured; one was synthesized for 2 d at 1050°C, and the other one was done for 1 d at 1100°C. All of the diffraction data were precisely refined by the Rietveld method, and we confirmed that there was no clear anomaly on the temperature dependence of the lattice constants around T
c for both samples. The difference in sample synthesis procedures affects the profile shapes of the 00l reflections, whereas the hh0 lines are almost the same.
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Sadhna Singh
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2477-2479
Published: 2002
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A B1-B2 transition in chalcogenides has been studied using three body potential approach upto 40 GPa. Phase transition pressures, volume collapses are found to be closed to experimental results. High phase transition pressures in CaSe and CaTe can be attributed to large cation anion differences. High-pressure elastic behaviour (second order elastic constants and their combinations) shows a sudden change at the phase transition pressure.
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Yasusada Yamada, Tomoyuki Takakura
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2480-2484
Published: 2002
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We investigate theoretically the structural aspect of the characteristic features in the vicinity of the metal-insulator phase boundary in perovskite-based manganites. We develop a phenomenological treatment based on Ginzburg-Landau type formalism in which the elastic energies such as Jahn-Teller energy, phonon energy and the bulk strain energy are explicitly taken into account. The two important features observed commonly at the phase boundary; incommensurate orbital order and two-phase coexistence are reproduced as the stable states in the two dimensional model system.
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Keiji Saito, Seiji Miyashita
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2485-2488
Published: 2002
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We study mechanism of magnetic energy transport, motivated by recent measurements of the thermal conductivity in low dimensional quantum magnets. We point out a possible mechanism of enhancement of the thermal conductivity in gapped magnetic system, where the magnetic energy transport plays a crucial role. This mechanism gives an interpretation for the recent experiment of CuGeO
3, where the thermal conductivity depends on the crystal direction.
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Shinji Watanabe, Kazumasa Miyake
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2489-2499
Published: 2002
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It is shown that anomalous properties of UGe
2 can be understood in a unified way on the basis of a single assumption that the superconductivity is mediated by the coupled SDW and CDW fluctuations induced by the imperfect nesting of the Fermi surface with majority spins at T=T
x(P) deep in the ferromagnetic phase. Excess growth of uniform magnetization is shown to develop in the temperature range T<T
x(P) as a mode-coupling effect of coupled growth of SDW and CDW orderings, which has been observed by two different types of experiments. The coupled CDW and SDW fluctuations are shown to be essentially ferromagnetic spin fluctuations which induce a spin-triplet p-wave attraction. These fluctuations consist of two modes, spin and charge fluctuations with large momentum transfer of the nesting vector. An anomalous temperature dependence of the upper critical field H
c2(T) such as crossing of H
c2(T) at P=11.4 kbar and P=13.5 kbar, can be understood by the strong-coupling-superconductivity formalism. Temperature dependence of the lattice specific heat including a large shoulder near T
x is also explained quite well as an effect of a kind of Kohn anomaly associated with coupled CDW-SDW transition.
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Katsunori Wakabayashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2500-2504
Published: 2002
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Lattice vacancy effects on electrical conductance of nanographite ribbon are investigated by means of the Landauer approach using a tight binding model. In the low-energy regime ribbons with zigzag boundary provide a single conducting channel whose origin is connected with the presence of edge states. It is found that the chemical potential dependence of conductance strongly depends on the difference (Δ) of the number of removed A and B sublattice sites. The large lattice vacancy with Δ ≠ 0 shows 2Δ zero-conductance dips in the single-channel region, however, the large lattice vacancy with Δ=0 has no dip structure in this region. The connection between this conductance rule and the Longuet-Higgins conjecture is also discussed.
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Tsuneya Ando
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2505-2511
Published: 2002
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In a self-consistent Born approximation the dynamical conductivity is calculated in a metallic carbon nanotube. To the lowest order in scattering strength the Drude conductivity is given by a delta function of the frequency except in the presence of scatterers with range shorter than the lattice constant. When effects of other bands are included, the Drude conductivity is broadened and the static limit of the conductivity becomes finite. In the case of scatterers with range shorter than the lattice constant, the low-frequency conductivity is given by a conventional Drude conductivity with finite relaxation time.
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Hideo Yoshioka, Yoko Okamura
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2512-2519
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Tomonaga-Luttinger-liquid theory is formulated for metallic carbon nanotubes with open boundaries. Both cases of single- and multi-wall nanotubes are discussed. Based on this theory, spatial variation of the charge density from an edge is investigated with taking account of the shift of the chemical potential which expresses the carrier injection to the nanotube. The charge density has the spatially independent part and the oscillatory component. Roles of Coulomb interaction on the amplitude of the oscillation, the wavenumbers of it and the uniform component of the charge density are clarified.
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Tomomi Kikuta, Yukihiro Shimizu
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2520-2525
Published: 2002
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The amplitude of the de Haas-van Alphen (dHvA) oscillation in the superconducting mixed state, which is measured by the field modulation method, is calculated. We investigate the effects of the superconducting eddy currents on the voltage signal from a pick-up coil, assuming that a finite conductivity, which may originate from the flux flow for example, exists in the mixed state. In a material which has a small Fermi surface, the Shubnikov-de Haas (SdH) effect contributes to the voltage signal in addition to the dHvA effect; therefore the amplitude of the voltage becomes larger than that of only the dHvA effect. In a material which has a large Fermi surface, the amplitude is hardly affected by the SdH effect and becomes smaller due to the skin effect. The present results have the same tendency with the experimental data of NbSe
2 as an example of a small Fermi surface and V
3Si as an example of a large Fermi surface.
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Kazuo Hatakeyama, Shuichiro Anzai, Hajime Yoshida, Takejiro Kaneko, Sh ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2526-2533
Published: 2002
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It is known that Cr
5Te
8, V
5Te
8 and Ti
5Te
8 are ferromagnetic, weakly or nearly antiferromagnetic, and Pauli-paramagnetic materials, respectively. The temperature dependence of magnetization in (Cr
1-yV
y)
5Te
8 is measured, from which the magnetic phase diagram and the generalized Curie-Weiss (GCW) parameters are investigated. Gross feature of dT
C(Curie temperature)/dy<0 is similar to that of dT
C/dx<0 in (Cr
1-xTi
x)
5Te
8, except dT
C/dy ≅ 0 near y=0. No qualitative difference in the GCW parameters is observed in the low ranges of y and x. The pressure (P) dependence of T
C for the low ranges of y and x is investigated by measuring permeability. The observed nonlinear P-dependence of T
C is systematically described with T
C,P=T
C,P=0 [1+ζP ] [1+ηP ]
2 for η < 0 and ζ > 0 with dη/dy < 0, dη/dx < 0, d ζ/dy>0 and dζ/dx > 0. The GCW, T
C,P=0, η and ζ parameters are connected to the spin fluctuation model for itinerant electron ferromagnetism proposed by Moriya. The obtained y and x dependence of GCW, T
C,P=0, η and ζ parameters is discussed on the view-point of the difference in electron correlation natures and magnetic states of Cr
5Te
8, V
5Te
8 and Ti
5Te
8.
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Akimasa Sakuma
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2534-2538
Published: 2002
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By the first-principles calculations both for electronic structures and effective exchange constants, we investigate the stability of ferromagnetism of zinc-blende (ZB) type CrAs, and further examine a possibility of ferromagnetism of ZB type MnM (M=Si, Ge and Sn). ZB type CrAs, a half-metallic ferromagnet reported by Akinaga's group [Jpn. J. Appl. Phys.
39 (2000) L1118], is found to have an effective exchange constant (J
0=∑
i≠ 0J
i0) larger than 150 meV above the lattice constant of GaAs (a=5.65 Å), showing quite stable ferromagnetism above room temperature as was observed experimentally. We predict that ZB type MnM (M=Ge, Si, Sn) whose valence electron numbers are the same as that of CrAs also exhibit half-metallic ferromagnetism having a positive J
0 large enough at a=5.82 Å, indicating that the Curie temperatures are higher at least than room temperature.
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Kazuo Mukai, Masanobu Yanagimoto, Shinsuke Narimatsu, Hidesuke Maruyam ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2539-2545
Published: 2002
Released on J-STAGE: April 25, 2003
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The field dependence of the magnetization (H=0—55 T) of the mixed verdazyl radical crystals, ( p-CyDOV)
1-x( p-CyDTV)
x (x=0, 0.01, 0.02, 0.03, 0.05, and 0.07) was measured to study the doping effect of magnetic impurity ( p-CyDTV) on the organic spin-Peierls (SP) system, 3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl ( p-CyDOV) radical crystal, where the >C=O group in p-CyDOV is replaced by the >C=S group in p-CyDTV. The effect of doping on SP system is very remarkable. We have found that the high-field magnetization M(x,H) curves of the doped organic SP system below T
SP=15.0 K can be well explained by the sum of the magnetization (M) of the spin-Peierls state (C
SP(x)M
SP(H)), one dimensional (1D) Heisenberg antiferromagnet (C
1D-HAF(x)M
1D-HAF(H)), and Curie impurity (C
Curie(x)M
Curie(H)), where C
i(x) is the fraction of the i th contribution. The result suggests the coexistence of SP state and antiferromagnetic long-range order in the doped p-CyDOV radical system at low temperature.
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I. G. Kim, T. H. Yeom, D. Y. Jeong, A. R. Lim, S. H. Choh, K. S. Hong
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2546-2549
Published: 2002
Released on J-STAGE: April 25, 2003
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Temperature dependences of the nuclear spin-lattice relaxation time of
51V in BiVO
4 single crystals, undoped and doped with 1 mol% of Eu
2O
3, respectively, were measured in the temperature range of 140-400 K. The spin-lattice relaxation times, T
1s, of both samples were divided into the long and short components. For the doped crystal, the long component of the relaxation time is much shorter than those of the undoped crystal since the paramagnetic relaxation through Eu
3+ ions was dominant. From data of the undoped BiVO
4, it is found that the slow motion leads to the phase transition starting at 260 K, and its thermal activation energy is 0.033 eV. That is, we observed the thermally activated motion in ferroelastic which precedes the paraelastic phase transition.
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Galal A. Mohamad
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2550-2556
Published: 2002
Released on J-STAGE: April 25, 2003
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Optical and electrical properties of Ammonium sulfate crystals (AS) were investigated in the temperature range 250-350 K. Optical constants of AS crystal were calculated at room temperature. The optical absorption coefficient α was analyzed and interpreted to be due to the allowed direct transition, hence the values of the allowed direct energy gap E
g were calculated. The parameter σ characterizing the broadening of the absorption edge was investigated as a function of temperature. Both E
g and σ showed anomalies at 286 and 303 K. Domain structure observations in the temperature range 250-350 K revealed the starting of a ferroelastic phase of AS at 286 K. This structure contains sometimes three kinds of domains and sometimes with two kinds of domains for the temperatures from 286 up to 303 K. At temperatures higher than 303 K, a stable phase with three kinds of domains was observed. Anomalies in the electrical conductivity behavior were detected at 286 and 303 K. This implies the occurrences of possible phase transitions at these two different temperatures.
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Mizuho Fukaya, Yosuke Kayanuma, Minoru Itoh
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2557-2565
Published: 2002
Released on J-STAGE: April 25, 2003
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The effect of lattice relaxation of the outermost core hole in the Auger-free luminescence (AFL) in CsCl is studied by an extended deformable cluster model. It is proposed that the initial state of the AFL is a weakly self-trapped state of the core hole. A simple tight-binding calculation of the electronic states is carried out, and the AFL spectra at finite temperatures are calculated. The high energy band at 5.2 eV is assigned as originating from the transition of the self-trapped hole to the localized state in the valence band due to the attractive potential of the lattice deformation created in the initial state. The final state of the emission band at 4.5 eV is, on the other hand, the extended state in the valence band. The difference in the thermal broadening characteristic of these two bands is well simulated by the calculation.
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Taketoshi Kawai, Satoshi Hashimoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2566-2569
Published: 2002
Released on J-STAGE: April 25, 2003
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We have investigated the absorption spectra of Tl
+ centers doped in ammonium and cesium halides crystals with the CsCl structure up to the vacuum ultraviolet energy range. In the NH
4X:Tl
+ (X = Cl, Br) crystals, the A, B and C absorption bands due to the intraionic transitions in the Tl
+ ion are observed in the energy region below the fundamental absorption band edge of the host crystals. In the CsX:Tl
+ (X = Cl, Br, I) crystals, on the other hands, several absorption bands having no extremely different absorption intensity appear below the absorption band edge. The lowest absorption bands are assigned to the A absorption band, and other absorption bands have no feature of the B and C bands. The appearance of the absorption bands is remarkably different between the NH
4X:Tl
+ and CsX:Tl
+ crystals, in spite of the same ion arrangements around the Tl
+ ion which is surrounded by eight nearest-neighbor halogen ions. The difference of the absorption bands between the NH
4X:Tl
+ and CsX:Tl
+ crystals can be interpreted by that of the next nearest-neighbor cation around the Tl
+ ion.
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Rui-Hua Xie, Qin Rao
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2570-2571
Published: 2002
Released on J-STAGE: April 25, 2003
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Naoki Bessho, Seiji Miyahara, Yukiharu Ohsawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2572-2573
Published: 2002
Released on J-STAGE: April 25, 2003
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Yasuyuki Yagi, Haruhisa Koguchi, Yoichi Hirano, Hajime Sakakita, Toshi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2574-2575
Published: 2002
Released on J-STAGE: April 25, 2003
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Yoshihiro Ishibashi, Makoto Iwata
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2576-2577
Published: 2002
Released on J-STAGE: April 25, 2003
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Hideto Fukazawa, Yoshiteru Maeno
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2578-2579
Published: 2002
Released on J-STAGE: April 25, 2003
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Hiroki Nakano, Seiji Miyashita
Article type: General Physics
Subject area: Mathematical methods in physics.
2002 Volume 71 Issue 10 Pages
2580-2581
Published: 2002
Released on J-STAGE: April 25, 2003
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