Finite Bias Anomaly in the Subgap Conductance of Superconductor-GaAs Junctions

Abstract

We measure the subgap conductance across a superconductor-GaAs junction at low temperature. Below $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4\mathrm{K}$ we observe a zero bias conductance peak. For the first time, we observe that at even lower temperatures ( $T\ensuremath{\le}0.8\mathrm{K}$), the conductance peak is shifted to a finite voltage. Application of a magnetic field restores a zero bias conductance peak. This is consistent with theoretical predictions for superconducting-semiconducting junctions in the regime where the contact conductance is larger than the coherent semiconductor conductance.