Influence of the temperature on the depinning transition of driven interfaces

We study the dynamics of a driven interface in a two-dimensional random-field Ising model close to the depinning transition at small but finite temperatures T using Glauber dynamics. A square lattice is considered with an interface initially in (11)-direction. The drift velocity v is analyzed for the first time using finite size scaling at T = 0 and additionally finite temperature scaling close to the depinning transition. In both cases a perfect data collapse is obtained from which we deduce beta = 1/3 for the exponent which determines the dependence of v on the driving field, nu = 1 for the exponent of the correlation length and delta = 5 for the exponent which determines the dependence of v on T.Comment: 5 pages, Latex, Figures included, to appear in Europhys. Let

Modelling the energy gap in transition metal/aluminium bilayers"

We present an application of the generalised proximity effect theory.Comment: 15 pages, 11 figures, presented at workshop on low temperature superconducting electronics at the University of Twente, The Netherland

Supercurrent in a mesoscopic proximity wire

Recent experiments on the proximity induced supercurrent in mesoscopic normal wires revealed a surprising temperature dependence. They suggest clean-limit behavior although the wires are strongly disordered. We demonstrate that this unexpected scaling is actually contained in the conventional description of diffusive superconductors and find excellent agreement with the experimental results. In addition we propose a SQUID-like proximity structure for further experimental investigations of the effects in question.Comment: 6 pages LaTeX, 4 postscript figures; to appear in J. Low Temp. Phys. (Proceedings of WSS '96

Magnetic breakdown in a normal-metal - superconductor proximity sandwich

We study the magnetic response of a clean normal-metal slab of finite thickness in proximity with a bulk superconductor. We determine its free energy and identify two (meta-)stable states, a diamagnetic one where the applied field is effectively screened, and a second state, where the field penetrates the normal-metal layer. We present a complete characterization of the first order transition between the two states which occurs at the breakdown field, including its spinodals, the jump in the magnetization, and the latent heat. The bistable regime terminates at a critical temperature above which the sharp transition is replaced by a continuous cross-over. We compare the theory with experiments on normal-superconducting cylinders.Comment: 7 pages Revtex, 3 Postscript figures, needs psfig.te

Density of States and Energy Gap in Andreev Billiards

We present numerical results for the local density of states in semiclassical Andreev billiards. We show that the energy gap near the Fermi energy develops in a chaotic billiard. Using the same method no gap is found in similar square and circular billiards.Comment: 9 pages, 6 Postscript figure

Superconductive properties of thin dirty SN bilayers

The theory of superconductivity in thin SN sandwiches (bilayers) in the diffusive limit is developed within the standard Usadel equation method, with particular emphasis on the case of very thin superconductive layers, d_S << d_N. The proximity effect in the system is governed by the interlayer interface resistance (per channel) \rho_{int}. The case of relatively low resistance (which can still have large absolute values) can be completely studied analytically. The theory describing the bilayer in this limit is of BCS type but with the minigap (in the single-particle density of states) E_g << \Delta substituting the order parameter \Delta in the standard BCS relations; the original relations are thus severely violated. In the opposite limit of an opaque interface, the behavior of the system is in many respects close to the BCS predictions. Over the entire range of \rho_{int}, the properties of the bilayer are found numerically. Finally, it is shown that the results obtained for the bilayer also apply to more complicated structures such as SNS and NSN trilayers, SNINS and NSISN systems, and SN superlattices.Comment: 15 pages (including 10 EPS figures), REVTeX. Version 2: minor changes; added references, a note is added concerning applicability of our results to SNINS and NSISN systems. To appear in Phys. Rev. B on March 1, 200

Anomalous proximity effect in d-wave superconductors

The anomalous proximity effect between a d-wave superconductor and a surface layer with small electronic mean free path is studied theoretically in the framework of the Eilenberger equations. The angular and spatial structure of the pair potential and the quasiclassical propagators in the interface region is calculated selfconsistently. The variation of the spatially-resolved quasiparticle density of states from the bulk to the surface is studied. It is shown that the isotropic gapless superconducting state is induced in the disordered layer.Comment: 6 pages, 5 postscript figures. Submitted to Phys.Rev.

Domain wall superconductivity in superconductor/ferromagnet bilayers

We analyze the enhancement of the superconducting critical temperature of superconducting/ferromagnetic bilayers due to the appearance of localized superconducting states in the vicinity of magnetic domain walls in the ferromagnet. We consider the case when the main mechanism of the superconductivity destruction via the proximity effect is the exchange field. We demonstrate that the influence of the domain walls on the superconducting properties of the bilayer may be quite strong if the domain wall thickness is of the order of superconducting coherence length.Comment: 8 pages, 2 figure

The current-phase relation in Josephson tunnel junctions

The $J(\phi)$ relation in SFIFS, SNINS and SIS tunnel junctions is studied. The method for analytical solution of linearized Usadel equations has been developed and applied to these structures. It is shown that the Josephson current across the structure has the sum of $\sin \phi$ and $\sin 2\phi$ components. Two different physical mechanisms are responsible for the sign of $\sin 2\phi$. The first one is the depairing by current which contributes positively to the $\sin 2\phi$ term, while the second one is the finite transparency of SF or SN interfaces which provides the negative contribution. In SFIFS junctions, where the first harmonic vanishes at 0 - $\pi$ transition, the calculated second harmonic fully determines the $J(\phi)$ curve.Comment: 6 pages, 2 figure

Cryptoferromagnetic state in superconductor-ferromagnet multilayers

We study a possibility of a non-homogeneous magnetic order (cryptoferromagnetic state) in heterostructures consisting of a bulk superconductor and a ferromagnetic thin layer that can be due to the influence of the superconductor. The exchange field in the ferromagnet may be strong and exceed the inverse mean free time. A new approach based on solving the Eilenberger equations in the ferromagnet and the Usadel equations in the superconductor is developed. We derive a phase diagram between the cryptoferromagnetic and ferromagnetic states and discuss the possibility of an experimental observation of the CF state in different materials.Comment: 4 pages, 1 figur