Synchronized Andreev transmission in SNS junction arrays

We construct a nonequilibrium theory for the charge transfer through a diffusive array of alternating normal (N) and superconducting (S) islands comprising an SNSNS junction, with the size of the central S island being smaller than the energy relaxation length. We demonstrate that in the nonequilibrium regime the central island acts as Andreev retransmitter with the Andreev conversions at both NS interfaces of the central island correlated via above-the-gap transmission and Andreev reflection. This results in a synchronized transmission at certain resonant voltages which in experiments is seen as a sequence of spikes in the differential conductivity.