Voltage and temperature dependence of current noise in double-barrier normal-superconducting structures

We study theoretically the current-noise energy (voltage bias and temperature) dependence for a N-N'-S structure, where N and S stand for bulk normal metal and superconductor, respectively, and N' for a short diffusive normal metal. Using quasiclassical theory of current fluctuations we determine the noise for arbitrary distributions of channel transparencies on both junctions. The differential Fano factor turns out to depend on both junction transparencies and the ratio of the two conductances. We discuss analytically the coherent and incoherent regimes and the case when one of the two conductances dominates the other one. Measurement of differential conductance and noise can be used to probe the channel distribution of the interfaces. We discuss recent experiments in the light of our results. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006