Superconductive properties of thin dirty superconductor-normal-metal bilayers - art. no. 094518

The theory of superconductivity in thin superconductor-normal-metal (SN) sa ndwiches (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 g overned by the interlayer interface resistance (per channel) rho (int). The case of relatively low resistance (which can still have large absolute val ues) can be completely studied analytically. The theory describing the bila yer in this limit is of BCS type but with the minigap (in the single-partic le density of states) E-g<<Delta substituting the order parameter Delta in the standard BCS relations; the original relations are thus severely violat ed. In the opposite limit of an opaque interface, the behavior of the syste m is in many respects close to the BCS predictions. Over the entire range o f 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 co mplicated structures such as SNS and NSN trilayers, SNINS and NSISN systems , and SN superlattices.