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Hui–Hui Dai, Maxim Pavlov
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 11 Pages
3655-3657
Published: November 01, 1998
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In this article we present a new transformation between two integrable hierarchies of the Camassa-Holm equation and the Hunter-Saxton equation. For instance we present a transformation between the Harry-Dym equation and the extended Harry-Dym equation. Moreover, we describe a relationship between the Hunter-Saxton equation, which is the high-frequency limit of the Camassa-Holm equation, and the Sinh-Gordon equation by a reciprocal transformation.
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Masatoshi Shiino
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 11 Pages
3658-3660
Published: November 01, 1998
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Generalized relative entropies with a real parameter q are proposed for Markovian stochastic processes, and the associated H-theorem is proved. The proposed entropies play the role of a Lyapunov function as the standard relative entropy known as the Kullback-Leibler divergence does. The H-theorem can be applied to Tsallis statistics, and it is shown that the nonequilibrium free energy, consistently defined based on the generalized entropy in the framework of Tsallis statistics, monotonically decreases to attain its equilibrium value.
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Yukio Saito, Heiner Müller–Krumbhaar
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 11 Pages
3661-3663
Published: November 01, 1998
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The Eden model with a repulsive interaction between the cluster and the attached atoms shows a tendency to form ramified clusters. With the r
-3-potential caused by the strain in two dimensions, the clusters show a ramified structure on a short-length scale, but eventually become compact on a large-length scale. With a longer-ranged r
-2-potential, the Eden clusters become fractal, with fractal dimensions smaller than 2.
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Okiyasu Shimizu, Jun Watanabe, Keiichi Imakubo, Shizuo Naito
Subject area: Molecular spectra and interactions of molecules with photons.
1998 Volume 67 Issue 11 Pages
3664-3667
Published: November 01, 1998
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The phosphorescence quantum yield Φ
P (=einsteins emitted/einsteins absorbed by sensitizer) of singlet oxygen (
1O
2) was measured for an air-saturated CCl
4 solution of phenalenone (PH) used as a photosensitizer, by means of a photon-counting technique based on the use of a near-IR-sensitive photomultiplier. Employment of steady-state excitation allowed for the determination of the absolute quantum yield of Φ
P=(1.38± 0.05)× 10
-3 in CCl
4. The result was obtained by direct comparison of the areas under the corrected emission spectra of
1O
2 and of quinine bisulfate (QBS) in 1N H
2SO
4 as a luminescence standard.
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Koji Ohkitani
Subject area: Fluid dynamics.
1998 Volume 67 Issue 11 Pages
3668-3671
Published: November 01, 1998
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In order to characterize the vortex stretching process in turbulence, a comparison is made numerically between nonlinear vortex stretchingand a linear stretching process of a passive vector.It is found that the passive vector is stretched more intensely than the vorticity. The physical meaning and the underlying mechanism of this effect are discussed.
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Noriyuki Hatakenaka
Subject area: Quantum fuids and solids: liquid and solid helium.
1998 Volume 67 Issue 11 Pages
3672-3674
Published: November 01, 1998
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The Josephson effect under particle-number restriction is investigated based on the Feynman two-state model. The existence of a new dynamical mode of the Josephson phase, at the metastable state inherent in such a restricted situation, is shown. The new mode describes a number of features recently observed in a superfluid
3He weak-link system.
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Masahide Sato, Makio Uwaha
Subject area: Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties).
1998 Volume 67 Issue 11 Pages
3675-3678
Published: November 01, 1998
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We study the growth law of step bunches formed by the drift of adatoms in a one-dimensional step model with conservation of atoms. The simulation result shows that the terrace size between bunches grows as a power of time L-- t
β with β=1/2 irrespective of the step interaction. The exponent agrees with experiment on Si(111) surface. The average step distance in a bunch is also related to the step interaction potential. A simple theoretical picture, based on a hierarchical bunching of steps, explains these results.
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Satoshi Nishimoto, Yukinori Ohta
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3679-3682
Published: November 01, 1998
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Optical conductivity of the trellis lattice t-J model at quarter filling is calculated by an exact-diagonalization technique on small clusters, whereby the valence state of V ions of NaV
2O
5 is considered. We show that the experimental features at --1 eV, including peak positions, presence of shoulders, and anisotropic spectral weight, can be reproduced in a reasonable range of parameter values, only by assuming that the system is in the charge disproportionated ground state. Possible reconciliation with experimental data suggesting the presence of uniform ladders at T>T
c is discussed.
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Tsuyoshi Hatano, Takashi Tameshige, Yoshimasa Isawa
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1998 Volume 67 Issue 11 Pages
3683-3686
Published: November 01, 1998
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Quantized current plateaus appear in the I-V characteristics of turnstile devices realized by modulating the tunnel barriers with a radio frequency (rf) signal of frequency f and phase difference π. We report two new results. (1) New fine structures resulting from the quantized level spacing Δ E appear. Then, the quantized current flows through the barriers via several excited states of the system with a fixed number of electrons, as the source drain voltage increases. These structures are smeared out when the temperature k
BT becomes comparable to Δ E. However the quantized plateaus remain. The quantized plateaus are washed out when k
BT becomes comparable to the charging energy e
2/C, where C is the capacitance of the dot. (2) When the rf frequency f becomes larger than the leakage current J(f=0)/e, which is the time-averaged current at the frequency f=0, the time-averaged current J
dc is quantized in the adiabatic regime. On the other hand, when f is smaller than J(f=0)/e, J
dc is much larger than the quantized current.
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Hiroshi Matsui, Masanori Yamaguchi, Yoshiyuki Yoshida, Atsushi Mukai, ...
Subject area: Superconductivity.
1998 Volume 67 Issue 11 Pages
3687-3690
Published: November 01, 1998
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Ultrasound velocity measurements based on a phase comparison method for four different modes have been done on a copper-free layered perovskite superconductor Sr
2RuO
4 with T
c = 1.2 K. Anomalous softening is observed in the longitudinal C
11 and C
33 modes below 108 K, which is attributed to the coupling of the electronic states to the strain with Γ
1 representation in the tetragonal point group D
4h. The discontinuous change of the slope in C
11 and C
33 at T
c is basically explained by the second-order strain dependence of T
c, ∂
2T
c/∂ε
2uk. From the initial slope of the upper critical field H
c2, the anisotropy ratio in the coherence length is found to be 28, in agreement with previous ac susceptibility measurements. Acoustic de Haas-van Alphen oscillations for the cylindrical α-Fermi surface with 3.2m
0 are observed in C
33 as a function of the magnetic field applied perpendicular to the Q2D conducting plane. The area coefficient is evaluated to be |Λ
zz| = 20±5 from the Kataoka-Goto model. The multiband term |Λ
zzm| contributes dominantly to |Λ
zz|, which corresponds to the interband charge transfer.
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Hiori Kino, Hiroshi Kontani
Subject area: Superconductivity.
1998 Volume 67 Issue 11 Pages
3691-3694
Published: November 01, 1998
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We study the electronic states of the anisotropic triangular latticeHubbard model at half-filling, which is a simple effectivemodel for the organic superconducting κ-BEDT-TTF compounds.We treat the effect of the Coulomb interactionby the fluctuation exchange (FLEX) method, and obtainthe phase diagram of this model for various sets of parameters.It is shown that d-wave superconductivity is realized in a wide regionof the phase diagram, next to the antiferromagnetic states.The obtained phase diagram explains well the characteristics of theexperimentalresults.
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Hisashi Kondo, Toru Moriya
Subject area: Superconductivity.
1998 Volume 67 Issue 11 Pages
3695-3698
Published: November 01, 1998
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Spin fluctuation-induced superconductivity in two-dimensional organic compounds such as κ-(ET)
2X is investigated using a simplified dimer Hubbard model with a right-angled isosceles triangular lattice (transfer matrices -τ, -τ
′). The dynamical susceptibility and the self-energy are calculated self-consistently within the fluctuation exchange approximation, and the value for T
c obtained by solving the linearized Eliashberg-type equations is in good agreement with the experimental results. The pairing symmetry is of the d
x2-y2 type. The calculated \left( U/τ \
ight)-dependence of T
c compares qualitatively well with the observed pressure dependence of T
c. Varying the value for τ
′/τ from 0 to 1, we interpolate between the square lattice and the regular triangular lattice and find first that relative values of T
c for κ-(ET)
2X and cuprates are reasonably explained and second that T
c tends to decrease with increasing τ
′/ τ. No superconductivity is found for τ
′/τ = 1, the regular triangular lattice.
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Yasumasa Hasegawa
Subject area: Superconductivity.
1998 Volume 67 Issue 11 Pages
3699-3702
Published: November 01, 1998
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The Josephson effect between triplet and singletsuperconductors is studied. Josephson current can flow between triplet and singletsuperconductorsdue to the spin-orbit coupling in the spin-triplet superconductorbut it is finite only when the triplet superconductor has L
z=-S
z=± 1, where L
z and S
z are theperpendicular components of orbital angular momentum and spinangular momentum of the triplet Cooper pairs, respectively. The recently observed temperature and orientationaldependence of the critical currentthrough a Josephson junction between UPt
3 and Nb is investigated by considering a nonunitary triplet state.
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Yoshio Kitaoka, Tatsuo Kobayashi, Akihiro Koda, Hayato Wakabayashi, Yo ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3703-3706
Published: November 01, 1998
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From the
7Li nuclear magnetic resonance (NMR) and specific heatmeasurements of LiNiO
2, consisting of a spin-1/2 triangular lattice, itis demonstrated that the previously suggested spin-glass-like freezingbelow T
sg=8, K, which is caused by defects of Li ions, is not the trueground state, but rather a quantum disordered state is realized without aspin gap. This state is characterized by power-law behavior of thetemperature dependence of the specific heat below 0.5, K. A spin-liquidstate with short-range ferromagnetic correlations is suggested from newinsight into the frustration of orbital ordering for doubly degeneratee_g shells in the triangular lattice.
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Hiroyuki Deguchi, Shunsaku Sumoto, Seishi Takagi, Masaki Mito, Tatsuya ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3707-3710
Published: November 01, 1998
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Magnetic measurements have been performed to investigate nonmagnetic impurity effects on a Zn-doped ladder system (Cu
1-xZn
x)
2(C
5H
12N
2)
2Cl
4. The paramagnetic contribution in the susceptibility χ
′ of the Zn-doped system increases with increasing x below the gap temperature. The susceptibility obeys the Curie law in the temperature range between 0.5, K and 2, K. However, at temperatures below 0.5, K, χ
′T drops with decreasing temperature, which suggests the crossover in the Curie constant as predicted by Sigrist and Furusaki [J. Phys. Soc. Jpn. 65 (1996) 2385]. Magnetization curves of the Zn-doped system are compared with that of the pure system. The impurity-induced spin behaves like a paramagnetic S=1/2 spin and the spin-gap state survives even in the Zn-doped system with the content x up to 0.117. These results seem to originate from the weak interladder interaction of the system.
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Shoji Yamamoto, Tohru Sakai
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3711-3714
Published: November 01, 1998
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Static and dynamic structure factors of Heisenberg ferrimagnetic spin chains are numerically investigated. There exist two distinct branches of elementary excitations, which exhibit ferromagnetic and antiferromagnetic aspects. The ferromagnetic feature is smeared out with the increase of temperature, whereas the antiferromagnetic one persists up to higher temperatures. The scattering intensity is remarkably large at lower boundaries of the ferromagnetic and antiferromagnetic spectra. All these observations are consistent with the ferromagnetic-to-antiferromagnetic crossover in the thermal behavior which has recently been reported.
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Sebastian Luther, Hiroyuki Nojiri, Mitsuhiro Motokawa, Masahiko Isobe, ...
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 Volume 67 Issue 11 Pages
3715-3717
Published: November 01, 1998
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Transitions between the singlet ground state and the first excited triplet state in NaV
2O
5 have been observed by means of submillimeter wave ESR for the first time. The distinct Zeeman splitting clearly indicates that the first excited state is a triplet state. The singlet-triplet energy gap at zero field has been determined as Δ = 8.13 ,meV at T = 4.2K. A considerable anisotropy of the absorption intensity with respect to the magnetic field orientation has been observed. The intensity is strongest for B // a and weakest for B // c. We propose that this result can be explained by including in the Hamiltonian the Dzyaloshinsky-Moriya interaction which breaks the selection rule.
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Yosuke Kayanuma, Hiroyuki Nakayama
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1998 Volume 67 Issue 11 Pages
3718-3720
Published: November 01, 1998
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It is shown that the concept of the interaction mode can be extendeduniquely to multilevel electron-phonon systems. For a model of a localizedn-level system linearly coupled with many mode phonons in the diagonalform, we can construct n interaction modes that carry the entirerelaxation energy, while the rest modes can be regarded as forming areservoir of the interaction mode.
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Kwok W. Chow, Derek W. C. Lai
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 11 Pages
3721-3728
Published: November 01, 1998
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An exact 2-soliton expression is obtained for the Manakov system, a special, coupled set of nonlinear Schrödinger equations. The solution permits different asymptotic states for the components in the far field. A `coalescence' of wavenumbers is considered from the perspective of the Hirota bilinear operator. This is roughly equivalent to a double (or in general multiple) pole solution in the language of the inverse scattering transform. Physically counterpropagating waves will occur. With the help of computer algebra software a 3-soliton solution is derived. Coalescence of eigenvalues is investigated. Temporal modulation of the amplitude is observed.
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Rei Inoue, Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1998 Volume 67 Issue 11 Pages
3729-3733
Published: November 01, 1998
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The Bogoyavlensky lattice with discrete time is studied.We introduce an integrable integro-difference equation, which isobtained by taking an interaction range to infinity in the Bogoyavlensky lattice.Its integrability is shown by constructing the Lax form.Also studied is a relationship with the fully discrete W currents.
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Paul Woafo
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 11 Pages
3734-3741
Published: November 01, 1998
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We consider the numerical simulation of the dynamics of topological solitons in coupled Sine-Gordon chains. Oscillating bound states and mutual pinning of solitons belonging to different chains are observed. The interaction of pairs of solitons with localized impurities is also investigated. Symmetrical and antisymmetrical impurity modes are excited in the case of an attractive impurity with the same strength in both chains. We find that the critical velocity below, which resonant interactions between the solitons and impurity modes take place, increases as we move from the highly repulsive state to the highly attractive state. In the case of attractive impurities with different strengths, the pair of solitons can be either captured, separated or transmitted with the formation of a moving bound state afterwards.
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Tosizumi Aoki
Subject area: Statistical physics and thermodynamics.
1998 Volume 67 Issue 11 Pages
3742-3750
Published: November 01, 1998
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The two-time Green's function method is applied to the modified quantum Heisenberg model with the following exchange interactions: The interactions decay as inverse square of the distance between sites and have alternate positive and negative signs with increasing distance between sites; moreover, they work well only along the coordinate axes. The critical temperature and zero-temperature spin reduction are calculated for the one-, two- and three-dimensional cases. The temperature dependence of spin reductions in two and three dimensions is estimated in the low-temperature region. The critical behavior of long-range order and susceptibility is also investigated. Lastly, it is attempted to estimate the long-distance behavior of static correlation function in one dimension.
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Katsuhiko Fukasaku, Kyozaburo Takeda, Kenji Shiraishi
Subject area: Electronic structure of atoms and molecules: theory.
1998 Volume 67 Issue 11 Pages
3751-3760
Published: November 01, 1998
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The electronic structures of protein nanotubes (PNTB), whichare formed by the periodical stacking of cyclo-peptide-ring (CPR)rings, are theoretically investigated in terms of the ab initiocalculations. The inter-ring H bonds among the CPRs cause theelectronic interaction when CPRs are periodically stacked. Thisinteraction has a potential to delocalize electrons and holes alongthe tube axis as if the band conduction occurs through the bridging Hbonds. The protonation of this system is also investigated. Themigrated proton (charged H
* species) is expected to create theimpurity (acceptor) level in the band gap of the PNTB.
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Makoto Tomita, Kenshi Shimano
Subject area: Optics.
1998 Volume 67 Issue 11 Pages
3761-3768
Published: November 01, 1998
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We investigate the fluctuations of light transmitted through static disordered media in time and frequency domains. When the pulse duration of the incident light is much shorter than the typical time of flight through the medium, fluctuations appear both in time and frequency domains and the uncertainty relation, δ τ δ ω -- 1 or δ τ δ E -- (h/2π), holds good in these fluctuations. We discuss the necessary condition to observe this relation. Precise calculations of the correlation functions also reveal that the exact shape and width of the correlation functions depend on the pulse duration and the observation time. Experimental results with picosecond pulses through thick and thin samples show good agreement with the theoretical calculations.
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Daishin Uehara, Takeshi Iizuka, Takahi Hasegawa, Chihiro Matsuoka
Subject area: Mechanics, elasticity, and rheology.
1998 Volume 67 Issue 11 Pages
3769-3773
Published: November 01, 1998
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Interactions between nonlinear media and an object in it are studied theoretically and numerically using dynamical models. The KdV soliton is incidented to the object by numerical simulation and the generation of solitons are detected. The measured amplitudes coincide very well with the theoretical results.
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Yoshimitsu Amagishi, Tetsuya Miyazaki
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1998 Volume 67 Issue 11 Pages
3774-3778
Published: November 01, 1998
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A Mach probe is studied as a simple method to measure the plasma flow velocity (Mach number) along magnetic field lines. The probe was located behind the separator, which is movable along the field line, to avoid a recycling-like phenomenon that occurs owing to the plasma striking the separator. From the ratio of ion currents to the probe with to without the separator, the Mach number was deduced by applying a theory proposed by Chung [Phys. Plasmas 1 (1994) 2864]. Even though the theory is not neccesarily satisfactory for approximation of the viscosity term in fluid equations, the Mach number obtained from the Mach probe is compared fairly well with the real Mach number which was obtained from dispersion relations of the shear Alfvén wave drifting along or against the plasma flow.
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Koji Tanaka, Kazuo Minami, Takao Nagahama
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 11 Pages
3779-3786
Published: November 01, 1998
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The dispersion relation of quasi-TE
ls modes in sinusoidally corrugated metal wall slow wave structure with an annular electron beam is derived and analyzed numerically. Results of the numerical analysis for quasi-TE
11 mode and conventional TM
01 mode are compared with experimental results. TE
11 mode in addition to TM
01 mode microwave oscillation is observed near 2π mode region of operation. It is confirmed that oscillation property of both modes agree fairly well with numerically predicted values. The study of quasi-TE mode oscillation is required for an optimum design of a high power backward wave oscillator that works in a single frequency over a wide range of operating conditions.
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Tohru Kuroda, Hideo Sugama, Ryutaro Kanno, Masao Okamoto, Wendell Hort ...
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 11 Pages
3787-3793
Published: November 01, 1998
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The initial value problem of the toroidal ion temperature gradientmode is studiedbased on the Laplace transform of the ion gyrokinetic equation andthe electron Boltzmann relation with the charge neutrality condition.Due to the toroidal magnetic drift, the Laplace-transformed density andpotential perturbations have a branch cut as well as poleson the complex-frequency plane.The inverse Laplace transform shows that the temporal evolution ofthe density and potential perturbations consists of the normal modesand the continuum mode, which correspond to contributions fromthe poles and the branch cut, respectively.The normal modes have exponential time dependence with the eigenfrequenciesdetermined by the dispersion relation while the continuummode shows power-law decay oscillation.For the stable case, the long-time asymptotic behavior of the potentialand density perturbations is dominated bythe continuum mode which decays slowerthan the normal modes.
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Akira Yoshioka, Tomoya Tatsuno, Masahiro Wakatani
Subject area: The physics of plasmas and electric discharges.
1998 Volume 67 Issue 11 Pages
3794-3800
Published: November 01, 1998
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Resistive wall mode (RWM) is studied in a cylindrical plasmawith a uniform longitudinal plasma flow.In order to simplify the analysis, two steps current profile model is employed with a constant current densityj
0 for the inner region 0 ≤ r ≤ a
0 and a constant current density j
1 for the outer region a
0 ≤ r ≤ a.Also the resistive shell is assumed sufficiently thin.Current profiles from peaked ones to hollow ones are simulated by changing the ratio j
1 / j
0.Based on the incompressible MHD model, it is shown that RWM can be stabilized by adjusting the resistive wall position, when the shear Alfvén resonance appears inside the plasma column, with the increase of the uniform flow velocity.In this case the free energy destabilizing the RWM is absorbed in the plasma column through the shear Alfvén resonance.However, except when the RWM is close to the marginal state without a plasma flow, the flow velocity for stabilization is comparable to the sound velocity.
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Koun Shirai, Hiroshi Katayama–Yoshida
Subject area: Lattice dynamics and crystal statistics.
1998 Volume 67 Issue 11 Pages
3801-3808
Published: November 01, 1998
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The 527-cm
-1 Raman band of α-boron, which has beenrecently assigned as a librational mode, exhibits a very narrow linewidth. Themechanism of this narrow linewidth is studied from the viewpoint ofanharmonic effectsof phonons. The density of states which is responsible to the decay processes israther large. Anharmonic force constants of individual bonds are evaluated fromthe pressure dependence on the phonon frequencies, and are found to be notsmall.Accordingly, by these two factors only, the linewidth could not be as narrow asobserved. It is found that the essential cause of the narrow linewidth is itsexceptionally high frequency. This makes the thermal factor for theup-conversionprocesses small even at room temperature.
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Tsutomu Sato, Jun Suda
Subject area: Lattice dynamics and crystal statistics.
1998 Volume 67 Issue 11 Pages
3809-3815
Published: November 01, 1998
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The first-order Raman spectra of internal A1 and external modes in sintered hexagonal GeO
2 crystalline were measured in the temperature range of 293--873, K and the linewidths at these temperatures were obtained. The temperature dependence of the linewidths was analyzed using the phonon dispersion curves calculated on the basis of a rigid-ion model, and the results showed that it was caused approximately by the cubic anharmonic term in the crystal potential energy.
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Dai S. Hirashima, Hideaki Takahashi
Subject area: Quantum fuids and solids: liquid and solid helium.
1998 Volume 67 Issue 11 Pages
3816-3824
Published: November 01, 1998
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Wavevector dependence and temperature dependence of magnetic susceptibility of clean interacting fermion systems in two dimensions are investigated by a second order perturbation theory. It is found that the static susceptibility varies linearly with wavevector q in the long wavelength limit at T=0. It is also found that the uniform susceptibility varies linearly with temperature at low temperatures.
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Keita Kishigi
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3825-3834
Published: November 01, 1998
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We study the ordered states of the field induced spin density wave (FISDW) in the presence of an anion ordering potential at zero and finite temperature self-consistently. We obtain a new FISDW state stabilized in a strong potential region, by which we can explain recently obtained phase diagram of (TMTSF)_2ClO_4. The anomalous behavior of the so-called rapid oscillation in the transport and thermodynamics quantities is attributable to the new FISDW state.
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Yukio Hirano, Yoshiyuki Ono
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3835-3843
Published: November 01, 1998
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Dynamical process of the formation of a soliton pair from a photogenerated electron-hole pair in polyacetylene is studied numerically by adopting the SSH Hamiltonian. A weak local disorder is introduced in order to trigger the formation. Starting from an initial configuration with an electron at the bottom of theconduction band and a hole at the top of the valence band, separated by the Peierls gap, the time dependent Schröndinger equation for the electron wave functions and the equation of motion for the lattice displacements are solved numerically. After several uniform oscillations of the lattice system at the early stage, a large distortion corresponding to a pair of a soliton and an anti-soliton develops from a point which is determined by the location and type of the disorder. In some cases, two solitons run in opposite directions, leaving breather like oscillations behind, and in other cases they form a bound state emitting acoustic lattice vibrational modes.
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Eiji Tsuchida, Masaru Tsukada
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3844-3858
Published: November 01, 1998
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The adaptive finite-element method proposed in our previous work [Phys. Rev. B 54 (1996) 7602] is extended to fully self-consistent calculations of realistic materials. Our method is highly adaptive, sparse, parallel, and suited for the O(N) methods, thanks to the localized finite-element basis functions. Accurate ionic forces can also be calculated within practical time usage. Applications to the structural properties of diamond, c-BN, and the C
60 molecule, and molecular dynamics within O(N
3) scaling are shown first, followed by detailed error analyses. Then the O(N) method based on the orbital formulation is realized within our approach.
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Masahiro Takashita, Haruyoshi Aoki, Christopher John Haworth, Takehiko ...
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3859-3866
Published: November 01, 1998
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We report a de Haas-van Alphen effect study of CeSb in thehigh-field ferromagnetic (F)and intermediate-field antiferromagnetic (AFF1) phases.In the F phase, the frequencies ofthe electron surfaces increase monotonically with pressure.On the other hand, the frequency ofone particular hole surface increases with pressure, while those of the other hole surfaces decrease slightly.The effective masses of all the hole surfaces increase similarlywith pressure, while those of the electron surfaces change little.In the AFF1 phase, other hole surfaces than theparticular one have qualitatively different pressure dependencefrom that in the F phase.The frequency changes both in the Fand AFF1 phases can be explainedby taking the anisotropic p-f mixing model into account.However, it is difficult to understandthe changes of the effective masses in termsof the f content expected for the p-f mixing model.
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Takashi Yanagisawa, Soh Koike, Kunihiko Yamaji
Subject area: Electron states in condensed matter.
1998 Volume 67 Issue 11 Pages
3867-3874
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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We propose a Monte Carlo method, which is a hybrid method of the quantumMonte Carlo method and variational Monte Carlo theory, to study the Hubbard model.The theory is based on the off-diagonal and the Gutzwiller type correlation factors which are taken into account by a Monte Carlo algorithm.In the 4×4 system our method is able to reproduce the exact results obtained by the diagonalization. An application is given to investigate the half-filled band case of two-dimensional square lattice.The energy is favorably compared withquantum Monte Carlo data.
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Nguyen Quang Bau, Tran Cong Phong
Subject area: Electronic transport in condensed matter.
1998 Volume 67 Issue 11 Pages
3875-3880
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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Analytic expressions for the absorption coefficient of a weak Electromagnetic Wave (EMW) by free carriers for the case of electron-optical phonon scattering in quantum wells are calculated by the Kubo-Mori method in two cases: ---The absence of a magnetic field. ---The presence of a magnetic field applied perpendicular to its barriers. A different dependence of the absorption coefficient on the temperature T of system, the electromagnetic wave frequency ω, the cyclotron frequency Ω (when a magnetic field is present), and characteristic parameters of a quantum well in comparison with normal semiconductors is obtained. The analytic expressions are numerically evaluated, plotted and discussed for a specific quantum well AlAs/GaAs/AlAs.
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Geraldo Magela e Silva, Paulo Hora Acioli, Yoshiyuki Ono
Subject area: Electronic transport in condensed matter.
1998 Volume 67 Issue 11 Pages
3881-3885
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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The propagation of charged solitons in a branching off conjugated polymer is studied. The soliton dynamics is numerically calculated using a 2-D extension of the Su-Schrieffer-Heeger Hamiltonian. We found that the propagation of a soliton through the bifurcation sites depends on the single-double bond configuration around these sites as well as the length of each branch. It is found that the soliton can be trapped, go through, or be reflected at the bifurcations. The implications for the setting up of molecular circuits are determined.
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Junji Yoshida, Tomi Ohtsuki, Yoshiyuki Ono
Subject area: Electronic transport in condensed matter.
1998 Volume 67 Issue 11 Pages
3886-3890
Published: November 01, 1998
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Ballistic transport properties in a two dimensional electron gas are studiednumerically, where magnetic fields are perpendicular to the plane oftwo dimensional electron systemsand periodically modulated both in x and y directions.We show that there are three types of trajectories of classical electronmotions in this system; chaotic, pinned and runaway trajectories.It is found that the runaway trajectories can explain the peaks ofmagnetoresistance as a function of external magnetic fields, which is believed to be related to the commensurability effect betweenthe classical cyclotron diameter and the period of magnetic modulation.The similarity with and difference from the results in the antidot latticeare discussed.
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Hiroyuki Miyake, Hiroshi Matsukawa
Subject area: Electronic transport in condensed matter.
1998 Volume 67 Issue 11 Pages
3891-3896
Published: November 01, 1998
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We study the effect of the dissipation on the quantum phase slippagevia the creation of “vortex ring”in charge density wave (CDW) systems.The dissipation is assumed to come from the interactionwith the normal electron near and inside of the vortex core.We describe the CDW by extracted macroscopic degreesof freedom, that is, the CDW phaseand the radius of the “vortex ring”, assume the ohmic dissipation, and investigate the effect in the context of semiclassicalapproximation.The obtained results are discussed in comparison with experiments.It turns out that the effect of such a dissipationcan be neglected in experiments.
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Takemi Kawada, Shunji Sugai
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3897-3900
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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Pressure dependence of the exchange integral J in Nd_2CuO_4 was investigated by high-pressure two-magnon Raman scattering. The superconducting transition temperatures T
C in electron-doped high T
C superconductors are known to be almost independent of pressure in contrast with hole-doped ones. The obtained dJ/dP=12.4, cm
-1/GPa is, however, nearly the same as those in the insulating phases of hole-doped high T
C superconductors.The pressure dependence of the hopping integral t
pd is much larger than those of hole-doped ones, because the pressure coefficient of the charge-transfer gap energy has an opposite sign from that of hole-dopable structure.
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Yusuke Wakabayashi, Nobuyoshi Wakabayashi, Tetsuo Kitai
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3901-3905
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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DyZn
2 has an orthorhombic CeCu
2-type structure. Between 29K and the Néel temperature of 35K, the magnetic structure is that of sinusoidal modulation characterized by a wavevector q
m=ζ
m c*, where ζ
m is approximately 0.45 (MAF). The magnetic moments are parallel to the b-axis and, hence, the modulation is transverse. Below 29K, the wavevector is 0.5 c* and the compound is a simple antiferro magnet. On this study, X-ray diffraction measurements were carried out on a single crystal of DyZn
2. There is an anomaly in the thermal expansion at the Néel temperature, and satellite peaks were observed at 2 q
m in the MAF phase. The amplitude of the lattice modulation u was observed to depend on ζ
m. The fact that the lattice modulation has wavevector 2 q_m has been examined on the basis of a model which takes into account modifications of the exchange interactions due to atomic displacements. Furthermore, the same model can explain the change of the thermal expansion. Measurements in magnetic fields up to 1.4T were also performed. A new satellite peak was observed at (0 0 6+ζ
m) in fields. The appearance of the new satellite peak is expected by the model. The magnetic phase diagram was determined by measurements of satellite peaks at various temperatures and magnetic fields.
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Yutaka Kobayashi, Takeo Takagi, Mamoru Mekata
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3906-3912
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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We have studied magnetic ordering of frustrated classical Ising spins on theantiferromagnetic corner-sharing tetrahedron lattices in one, two and three dimensionstogether with one dimensional triangle lattice by means of Monte Carlo simulation. If the interaction is confined to the nearest neighbors, the corner-sharing tetrahedron systemsin all dimensions exhibit no long range order and spins in each tetrahedron plaquette are in the six-folddegenerate antiferomagnetic ground state at low temperatures as governed by the “ice rule”. The residual entropy per spin of the two and three dimensional arrays of tetrahedra, 0.202k
B, indicates thease systems to be less frustrated than the triangular and the Kagomé lattices.The fact that no appericiable difference is observed between the two and the threedimensional lattices indicates that the ordering in each plaquette plays the most important role in the ordering process in these lattices. As temperature is raised, spins of each plaquette fluctuate predominantly between onlytwo states with reversed spin configurations of the six ground states due to the correlation among plaquettes. Simultaneous flip of the four spins in a plaquette gives rise to the fluctuations between the two ground states although each flip is composed of several steps of single or double flips.
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Hirotaka Manaka, Isao Yamada, Zentaro Honda, Hiroko Aruga Katori, Koic ...
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3913-3917
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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The compound (CH
3)
2CHNH
3CuCl
3 has recently been found to be an ideal ferromagnetic-antiferromagnetic alternating Heisenberg chain with the energy gap Δ/k=17-- 18, K [H.Manaka et al.: J. Phys. Soc. Jpn. 66 (1997) 564].When an external field H is applied to this compound, the energy gap should vanish at the critical field H
c1 = Δ/gμ
B.Just above H
c1, the three-dimensional magnetic long-range order is expected, if the interchain coupling exists. Motivated by this expectation, we performed specific heat measurements over a temperature range from 0.5 to 5, K applying H up to 12, T. As a result, we found a λ-type anomaly of specific heat over 10-- 12, T, which indicates a transition to the three-dimensional long range order. The temperature at which the λ-type anomaly appears increases with increasing H. The critical field obtained by extrapolating the curve of the λ peak position versus H is 9.0, T, which is close to that obtained from a magnetization measurement.
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Shin Miyahara, Matthias Troyer, David C. Johnston, Kazuo Ueda
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3918-3923
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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We study the spin-1/2 trellis lattice Heisenberg model, a coupled spin ladder system, both by perturbation around the dimer limit and by quantum Monte Carlo simulations. We discuss the influence of the inter-ladder coupling on the spin gap and the dispersion, and present results for the temperature dependence of the uniform susceptibility. The latter was found to be parameterized well by a mean-field type scaling ansatz. Finally we discuss fits of experimental measurements on SrCu_2O_3 and CaV_2O_5 to our results.
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Aya Ishigaki, Toru Moriya
Subject area: Magnetic properties and materials.
1998 Volume 67 Issue 11 Pages
3924-3935
Published: November 01, 1998
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Effects of temperature variation of the zero-point spin fluctuationson the self-consistent renormalization (SCR) theory of spin fluctuationsaround the magnetic instabilities are discussed.In two and three dimensional ferromagnets and three dimensional antiferromagnets the effect is mostly to renormalize the mode-modecoupling constant. The renormalized value, corresponding to the experimental value, has a finite upper bound corresponding to a divergent mean field value.In two-dimensional antiferromagnets the critical behaviors of the staggeredsusceptibility and the nuclear spin-lattice relaxation rate are modified by logarithmic corrections while this correction hardly appears in those of theelectrical resistivity and the specific heat.The temperature variation of the mean square local amplitude of the spindensity around the magnetic instability is studied by using a simplemodel for the dynamical susceptibility and isapplied to discuss a general trend in the magneto-volume effects in weakitinerant magnets.Possible origins of the large thermal expansion and the large low temperaturecoefficient of the specific heat in magnetically frustrated systems are also discussed.
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Shin–ichi Kuroda, Yukihiro Shimoi, Shuji Abe, Takanobu Noguchi, ...
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 Volume 67 Issue 11 Pages
3936-3944
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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Electron-nuclear double-resonance (ENDOR) spectra of undoped poly(paraphenylene vinylene) are well described by the spin density distribution of the polaron for finite electron-electron interactions. Theoretically calculated spin distribution using the Pariser-Parr-Pople model with intermediate strength of the interactions yields the maximum spin density of 0.09 at vinylene sites with the half-width of the distribution over four PPV monomer units. The non-monotonic form of distribution together with the signs of spin densities are confirmed with the ENDOR-induced ESR as well as electron-nuclear-nuclear triple resonance (TRIPLE). The observed extension of the polaron is larger than that of the soliton reported in polyacetylene, which may be related to the nature of the polaron in conjugated polymers being viewed as a bound soliton pair.
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Hidekazu Mukuda, Kenji Ishida, Yoshio Kitaoka, Kunisuke Asayama, Zhiqi ...
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1998 Volume 67 Issue 11 Pages
3945-3951
Published: November 01, 1998
Released on J-STAGE: October 01, 1999
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We report
17O-NMR studies in the normal state of high-quality single-crystal Sr
2RuO
4 with T
c--1.5 K, which has been identified as spin-triplet p-wave superconductor. From systematic measurements of the Knight shift and the nuclear spin-lattice relaxation time T
1 on the O(1) sites in the RuO
2 planes and the O(2) sites in the SrO layers, microscopic distribution of the spin density on the p orbitals and the anisotropy of low-frequency components of dynamical susceptibility χ( q, ω_n) have been unraveled as follows;(1) The spin susceptibility at the O(1) sites is much larger than that at the O(2) sites. (2) From the anisotropy in the Knight shift at the O(1) sites, it is shown that the spin density resides predominantly on the in-plane p_π orbitals hybridized with the 4d
xy orbitals. (3) From the pronounced anisotropy in (1/T
1T) at both sites developed below T
*--130K where the c-axis resistivity shows a metallic behavior, we have found that the low-frequency components of χ( q, ω
n) is highly anisotropic in contrast to the uniform spin susceptibility being isotropic.The in-plane components of χ( q, ω
n) at the O(1) sites are almost independent of wave number although they are exchange-enhanced, whereas its out-of-plane component is markedly enhanced by interlayer antiferromagnetic (AF) spin fluctuations below T
*-- 130K.(4) For the apical O(2) sites on which the p orbitals are hybridized with the 4d
xz, yz and p
c orbitals on the O(1) site, the in-plane components of χ( q, ω
n) are enhanced by AF-spin fluctuations as well.The AF-spin fluctuations develop as quasiparticles hop coherently along the c-axis below T
*. These characteristics of spin fluctuations are suggested to provide a new scenario based on the Hund's coupling as a possible mechanism of spin-triplet p-wave superconductivity in Sr
2RuO
4, not on analogy with
3He.
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Naohiko Yasuda, Hidehiro Ohwa, Jun Oohashi, Kenji Nomura, Hikaru Terau ...
Subject area: Dielectric properties and materials.
1998 Volume 67 Issue 11 Pages
3952-3957
Published: November 01, 1998
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Dielectric properties of the disordered and ordered Pb(In
1/2Nb
1/2)O
3 (abbreviated as PIN) single crystals were investigated in the range of temperature T from -70 to 200°C and of hydrostatic pressures p up to 0.7, GPa. For the disordered PIN, a typical dielectric dispersion which obeys the empirical Vogel-Fulcher relation was observed. Such dielectric dispersion strength was weakened with an increase in the degree of chemical ordering (S) at the B-site cations in the perovskite ABO
3, and then relaxor behavior disappears. The relaxor behavior was also weakened with increasing pressure up to 0.7, GPa for the quenched disordered PIN with S=0.2, whereas for the disordered PIN with S=0.4, the relaxor behavior was weakened with increasing pressure and then the antiferroelectric phase transition was induced by the application of pressure above 0.4, GPa. For the ordered PIN, the phase below the transition temperature was confirmed to be antiferroelectric by observation of P-E double hysteresis loops. The stability in the antiferroelectric phase was enhanced by S and also by the application of pressure.
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