Density of states and supercurrent in diffusive SNS junctions: Roles of nonideal interfaces and spin-flip scattering

We present a theoretical study of the density of states and supercurrent in diffusive superconductor-normal metal-superconductor (SNS) junctions. In particular, we study the influence on these two equilibrium properties of both an arbitrary transparency of the SN interfaces and the presence of spin-flip scattering in the normal wire. We show that the minigap that is present in the spectrum of the diffusive wire is very sensitive to the interface transmission. More importantly, we show that at arbitrary transparency the minigap replaces the Thouless energy as the relevant energy scale for the proximity effect, determining, for instance, the temperature dependence of the critical current. We also study in detail how the critical current is suppressed by the effect of spin-flip scattering, which can be due either to magnetic impurities or, under certain circumstances, to an external magnetic field. Our analysis based on the quasiclassical theory of diffusive superconductors can be very valuable in establishing quantitative comparisons between experiment and theory.