Anomalous behaviour of S/N mesoscopic structures near T_c

TL;DR

This paper reports the first observation of a non-monotonic conductance behavior near T_c in superconductor-normal junctions, supported by theoretical calculations using quasiclassical Green's functions.

Contribution

It introduces a theoretical model explaining the anomalous conductance maximum near T_c in S/N mesoscopic structures, aligning with experimental data.

Findings

Maximum conductance observed 20 mK below T_c

Theoretical calculations match experimental conductance peaks

Identified the peak's origin as related to subgap conductance

Abstract

We observe a maximum in the conductance of Aluminum / n-GaAs junctions at temperatures 20 mK lower than the superconducting transition temperature. This is the first observation of a non- monotonic behavior of the conductance near the superconducting transition in superconducting normal junctions. To accommodate this effect we calculate the full temperature dependence of the conductance of these structures, invoking quasiclassical Green's functions in the diffusive limit. In addition to the well-known low temperature peak at temperatures on the order of the Thouless energy, we find a maximum near the critical temperature. This peak has the same origin as the subgap conductance observed in superconducting-normal junctions at low temperatures. Its calculated magnitude and position are in good agreement with our experimental observation.