Current noise in long diffusive SNS junctions in the incoherent multiple Andreev reflections regime

Abstract

Spectral density of current fluctuations at zero frequency is calculated for a long diffusive SNS junction with low-resistive interfaces. At low temperature, $T\ensuremath{\ll}\ensuremath{\Delta},$ the subgap shot noise approaches linear voltage dependence, $S=(2/3R)(eV+2\ensuremath{\Delta}),$ which is the sum of the shot noise of the normal conductor and voltage independent excess noise. This result can also be interpreted as the 1/3-suppressed Poisson noise for the effective charge $q=e(1+2\ensuremath{\Delta}/eV)$ transferred by incoherent multiple Andreev reflections (MAR). At higher temperatures, anomalies of the current noise develop at the gap subharmonics, $eV=2\ensuremath{\Delta}/n.$ The crossover to the hot electron regime from the MAR regime is analyzed in the limit of small applied voltages.