[en] We study the mechanism of Mott type superconductor-insulator (S-I) transition with disorder effect in metallic thin film. The critical behavior of superconductivity is examined analytically by using the Matsubara-Matsuda model and the double-time Green's function. The critical value of disorder, sheet resistance corresponding to the transition point and the critical exponents ν and z are obtained

[en] Effect of disorder in metallic thin film is examined as a possible mechanism of the superconductor-insulator transition. The critical value of disorder corresponding to the transition point is found analytically by using Matsubara-Matsuda model and Green's function method

[en] On the basis of the interacting hole-spin model previously proposed, the temperature dependence of the longitudinal relaxation rate R of Cu NMR is calculated for the normal state. The rate is shown to consist of two terms: R = R_K + R_D. The term R_K represents Korringa-like relaxation with strong enhancement due to the presence of 3d localized spins, and R_D comes from the spin diffusion among localized 3d system. The latter is almost temperature independent. This result is in good agreement with recent experiments

[en] It is shown that there should exist in saturated films of superfluid ⁴He at low temperature a nonlinear surface wave described by the Korteweg-de Vries equation. The effect of surface tension makes the solitary wave cold, in contrast to very thin films discussed in a preceding paper. An electrostatic method is proposed to generate cold solitary waves. The asymptotic behavior can be found theoretically by the inverse scattering method. Estimates of parameters imply the possibility of observing each solitary wave separately

[en] A Schroedinger equation is examined which describes the motion of superfluid condensate in thin ⁴He films. The equation includes full nonlinearity arising from the van der Waals potential due to substrate. In contrast to the ordinary nonlinear Schroedinger equation ( vertical stroke psi vertical stroke ²psi type) which has been solved by inverse-scattering method, it is extremely difficult to apply such analytic method to our equation. Numerical study shows, however, that there indeed exist, in our system, solitons which have asymmetric shape, and are quite stable through collisions with each other and with fixed boundary walls. Thus the present work generalizes KdV-soliton theories for ⁴He films to the fully nonlinear case. (orig.)

[en] Marginal Fermi liquid theory proposed by Varma et al. is based on an assumption concerning the imaginary part of the polarization part. We investigate the consequences of this assumption paying full respect to the Ward-Takahashi identity, and find that the vertex corrections are of vital importance. Our result at the low-energy region is that Varma et al.'s assumption does not break the Fermi-liquid picture, as long as the low-energy excitations are concerned. (orig.)

[en] The possibility of maser action using a current-biased mesoscopic Josephson junction in a high-Q microcavity is discussed. A mesoscopic Josephson junction behaves like an artificial atom as far as the interaction with the photon field is concerned. Under a certain bias current, the Josephson open-quote open-quote atom close-quote close-quote is resonantly excited or pumped by quantum-mechanical fluctuations of the Josephson phase, i.e., macroscopic resonant tunneling. When the pumping overcomes the loss of photons from the cavity, maser action is possible. Quantum statistical properties of photons are also investigated numerically, taking into acount the microcavity effect on the basis of a Jaynes-Cummings model with pumping and cavity damping. We found that a mesoscopic Josephson junction within the high-Q microcavity acts as a thresholdless maser with sub-Poissonian photon statstics. copyright 1996 The American Physical Society

[en] It is shown that high-temperature superconductivity in cuprous oxide can be understood in terms of an interacting hole-spin model with superexchange and Kondo-type exchange interactions. Many important properties will be discussed, with special emphasis on the s-wave nature of Cooper pairs, reentrant behavior of T/sub c/, finite isotope effect, and for YBa₂Cu₃O/sub 7-//sub x/, strong correlation between superconducting transition temperature and Cu(1)-O(4) bond length. The isotope effect has an origin quite different from the Bardeen-Cooper-Schrieffer theory, and the calculated value of its coefficient a is consistent with the experimental value /similar to/0.02. The main results of NMR studies, i.e. the s-wave nature of Cooper pairs as observed in /sup 17/O nuclei, and some puzzling aspects of the Cu NMR relaxation rates are discussed on the basis of the proposed model. A possible explanation to the anomaly in Cu NMR is given. It is predicted that oxygen ions should show a small displacement below the superconducting transition temperature T/sub c/

[en] The authors identify the composition and basic structure of oxide superconductors with Tc in the 90 K range. They have a general formula ABa/sub 2/Cu/sub 3/O/sub 7+x/ (A = Y and lanthanide elements) and are an oxygen-deficient-perovskite structure. For A = La, this study shows the existence of stable ''123'' phase with Tc = 85 K in addition to K/sub 2/NiF/sub 4/ phase with Tc = 30 K. Systematic investigation of the lanthanide series reveals a clear relationship between the occurrence of superconductivity and ''123 structure''. It is also suggested that the transition temperature is determined essentially by copper-oxygen connectivity, and does not depend on the species of A atoms

[en] The Korteweg--de Vries (KdV) equation is derived from Landau two-fluid hydrodynamics applied to the thickness oscillation of the superfluid ⁴He film at low temperatures, where the main restoring force is van der Waals attraction from the substrate and the thermomechanical force due to phonons is a small correction. Since the usual third-sound generators and detectors are far wider than the individual solitons, the asymptotic solution of the KdV equation provided by the inverse scattering method is coarse-grained by regarding it as a continuous train of sharp pulses. The envelope so obtained will show a singular front proportional to (t-t₀)/sup -1/2/, where t₀ is the arrival time of the fastest soliton, and should therefore be observable with the appropriate experimental arrangement