Nonequilibrium Current Noise in Mesoscopic Disordered Superconductor–Normal-Metal–Superconductor Junctions

Current noise in superconductor--normal-metal--superconductor junctions is calculated within the scattering theory of multiple Andreev reflections. The noise exhibits subharmonic gap singularities at bias voltages eV0ex0ex=0ex0ex2Δ/n both in single-mode junctions with arbitrary transparency D and in multimode disordered junctions. The subharmonic structure is superimposed on a monotonic increase of the effective transferred charge q*0ex0ex=0ex0exSI(0)/2I with decreasing V. At small D, q* increases in steps. In diffusive junctions, the noise diverges at small V, SI(0)∝V^-1/2, and exhibits excess noise Sexc0ex0ex=0ex0ex2eIexc, where Iexc is the excess current, at large V.