Multiple Andreev reflections and enhanced shot noise in diffusive superconducting-normal-superconductor junctions

We study the de conductance and current fluctuations in mesoscopic diffusive SNS junctions at subgap applied voltages eV < 2 Delta. We find that in spite of the multiple Andreev reflections, the current-voltage characteristic of a long SNINS structure obeys Ohm's law. At the same time, nonequilibrium heating of subgap electrons produces giant shot noise with pronounced subharmonic gap structure which corresponds to stepwise growth of the effective transferred charge. At eV --> 0, the shot noise approaches the magnitude of the Johnson-Nyquist noise with the effective temperature T* = Delta/3. We analyze the role of inelastic scattering and present a criterion of strong nonequilibrium.