Phase coherence, quantization, and thermal fluctuations in SNS junctions

Abstract

Abstract Quasiparticles in the bound and continuum states of superconducting- normal-superconducting junctions are scattered by thermal fluctuations. The scattering rates are computed as functions of temperature and normal layer thickness. Phase coherence of the pair potential is broken, if more than half of the quasiparticles in the continuum states are scattered before crossing of the N-region once. For the corresponding critical quasiparticle life-time τKc (coherence time) the r.m.s. fluctuation of the phase difference 〈 χ 2 ( τ Kc )〉 1 2 is of the order of π. Except at very low temperatures the bound states are considerably more stable against thermal fluctuations than the continuum states so that even in the absence of phase coherence the size-dependent quantization of the Andreev spectrum exists for sufficiently large momenta normal to the layer boundaries.