We study the dc conductance and current fluctuations in mesoscopic diffusive SNS junctions at subgap applied voltages $\mathrm{eV}<\mathrm{}2\mathrm{}\Delta$. 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, non-equilibrium heating of subgap electrons produces giant shot noise with pronounced subharmonic gap structure which corresponds to stepwise growth of the effective transferred charge. At $\mathrm{eV}\to 0$, the shot noise approaches the magnitude of the Johnson-Nyquist noise with the effective temperature $T^{\star }=\Delta /3\mathrm{}$. We analyze the role of inelastic scattering and present a criterion of strong nonequilibrium.

• Received 22 January 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.2050