Theory of Interaction Effects in N-S Junctions out of Equilibrium

We consider a normal metal - superconductor (N-S) junction in the regime, when electrons in the normal metal are driven out of equilibrium. We show that the non-equilibrium fluctuations of the electron density in the N-layer cause the fluctuations of the phase of the order parameter in the S-layer. As a result, the density of states in the superconductor deviates from the BCS form, most notably the density of states in the gap becomes finite. This effect can be viewed as a result of the time reversal symmetry breaking due to the non-equilibrium, and can be described in terms of a low energy collective mode of the junction, which couples normal currents in N-layer and supercurrents. This mode is analogous to the Schmid-Sch\"{o}n mode. To interpret their measurements of the tunneling current, Pothier {\em et. al} [Phys. Rev. Lett. {\bf 79}, 3490 (1997)] had to assume that the energy relaxation rate in the normal metal is surprisingly high. The broadening of the BCS singularity of the density of states in the S-layer manifest itself similarly to the broadening of the distribution function. Mechanism suggested here can be a possible explanation of this experimental puzzle. We also propose an independent experiment to test our explanation.Comment: 16 pages, 2 .eps figure

Quantum superconductor-metal transition

We consider a system of superconducting grains embedded in a normal metal. At zero temperature this system exhibits a quantum superconductor-normal metal phase transition. This transition can take place at arbitrarily large conductance of the normal metal.Comment: 13 pages, 1 figure include

Nonlinear σ\sigma model for disordered superconductors

We suggest a novel nonlinear $\sigma$-model for the description of disordered superconductors. The main distinction from existing models lies in the fact that the saddle point equation is solved non-perturbatively in the superconducting pairing field. It allows one to use the model both in the vicinity of the metal-superconductor transition and well below its critical temperature with full account for the self-consistency conditions. We show that the model reproduces a set of known results in different limiting cases, and apply it for a self-consistent description of the proximity effect at the superconductor-metal interface.Comment: Revised version, 8 pages, 1 fig., revtex; final version, as published, contains a few corrections in the summar

Correlated electrons in the presence of disorder

Several new aspects of the subtle interplay between electronic correlations and disorder are reviewed. First, the dynamical mean-field theory (DMFT)together with the geometrically averaged ("typical") local density of states is employed to compute the ground state phase diagram of the Anderson-Hubbard model at half-filling. This non-perturbative approach is sensitive to Anderson localization on the one-particle level and hence can detect correlated metallic, Mott insulating and Anderson insulating phases and can also describe the competition between Anderson localization and antiferromagnetism. Second, we investigate the effect of binary alloy disorder on ferromagnetism in materials with $f$-electrons described by the periodic Anderson model. A drastic enhancement of the Curie temperature $T_c$ caused by an increase of the local $f$-moments in the presence of disordered conduction electrons is discovered and explained.Comment: 17 pages, 7 figures, final version, typos corrected, references updated, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

Zero asymptotics of Laurent-type Orthogonal Polynomials.

Let {hn(z)} be the sequence of polynomials, satisfying +0 hm(x) hn(x) x-n dp(x) = mn, 0 m n, where n [0, 2n], n N. For a wide class of weights dp(x) and under the assumption limn n/(2n) = [0, 1], two descriptions of the zero asymptotics of {hn(z)} are obtained. Furthermore, their analogues for polynomials orthogonal on [-1, 1] with respect to varying weights are considered. These results continue the study begun in [3]. © 1996 Academic Press, Inc

COMPARISON OF CHARACTERISTICS OF THE CONVERTER-FED MOTOR AT SUPPLY FROM THE SINGLE-PHASE NETWORK AND FROM THE SOURCE OF THE DIRECT CURRENT

Purpose. Now even more often in various cars and mechanisms converter-fed motors are used. Their comparative characteristics with motors which are supplied from a network of a direct current are necessary for definition of the specific moment of motors which are supplied from the single-phase alternating current main. Methodology. For the converter-fed motor with a ratio of teeth of the stator and a rotor 8/6 at supply from a single-phase network via the rectifier two groups of numerical experiments were carried out. Motor capacity with a constant frequency of rotation at various capacity of the capacitor at the exit of the rectifier and motor capacity at the current providing the most admissible excess of temperature of a winding are determined. Dependences of useful power on capacity size at the rectifier exit are received with a constant frequency of rotation, and also at invariable current. Results. On the basis of the made numerical experiment it is possible to conclude that due to fluctuation of tension (from 0 to 100 %) at the rectifier exit at power supply of the converter-fed motor from the single-phase alternating current main in comparison with the corresponding sizes at supply from a source of a direct current: • motor capacity at preservation of capacity of the capacitor at the exit of the rectifier and frequency of rotation decreases on 60 – 63 %; • at almost acceptable increase in capacity of the capacitor (approximately twice) power should be reduced by 50 %; • power deceleration at preservation of that size of current of the motor what took place at its food from a source of a direct current makes 40 % at preservation of size of capacity of the capacitor at the exit of the rectifier and 32 % at its doubling, the frequency of rotation decreases approximately on 13 – 15 %. Practical value. The specific moment can be determined by power sizes at single-phase supply, frequency of rotation and to the volume of a rotor, with an invariable frequency of rotation it decreases in comparison with the specific moment at power supply of the motor from a source of a direct current by 50 – 63 %