Reduction of Josephson critical current in short ballistic SNS weak links

Abstract

We present fully self-consistent calculations of the thermodynamic properties of three-dimensional clean SNS Josephson junctions, where S is an s-wave short-coherence-length superconductor and N is a clean normal metal. The junction is modeled on an infinite cubic lattice such that the transverse width of the S is the same as that of the N, and its thickness is tuned from the short to long limit. Both the reduced order parameter near the SN boundary and the short coherence length depress the critical Josephson current $I_c$, even in short junctions. This is contrasted with recent measurements on SNS junctions finding much smaller $I_cR_N$ products than expected from the standard (non-self consistent and quasiclassical) predictions. We also find unusual current-phase relations, a ``phase anti-dipole'' spatial distribution of the self-consistently determined contribution to the macroscopic phase, and an ``unexpected'' minigap in the local density of states within the N region.