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 eV=2Δ/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*=S_I(0)/2I with decreasing V. At small D, q* increases in steps. In diffusive junctions, the noise diverges at small V, S_I(0)∞V^−1/2and exhibits excess noise S_exc=2eI_excwhere I_exc is the excess current, at large V.