Multiple Andreev Reflections and Enhanced Shot Noise in Diffusive Superconducting-Normal-Superconductor Junctions

摘要: We study the dc conductance and current fluctuations in diffusive voltage biased SNS junctions with a tunnel barrier inside mesoscopic normal region. find that at subgap voltages, eV<2Delta/n, associated chain of n Andreev reflections is mapped onto quasiparticle flow through structure n+1 barriers connected by conductors. As result, current-voltage characteristic long SNINS obeys Ohm's law, spite complex multiparticle transport process. At same time, nonequilibrium heating electrons produces giant shot noise pronounced subharmonic gap which corresponds to stepwise growth effective transferred charge. eV\to 0, approaches magnitude Johnson-Nyquist temperature T^*=Delta/3, charge increases as (e/3)(1 + 2Delta/eV), universal ``one third suppression'' factor. analyse role inelastic scattering present criterion strong nonequilibrium.