Investigation of low-temperature I-V curves of high-quality Nb/Al-AlOx/Nb Josephson junctions

Abstract
A detailed experimental temperature dependence of the subgap current of high‐quality Nb/Al‐AlOx/Nb Josephson tunnel junctions is reported. The presence of a pronounced current rise at V≂Δ/e is observed. Comparison with the theoretical model for two‐particle tunneling is performed, but a substantial disagreement is found. At V<Δ/e the measured current is in remarkably good agreement with the single particle tunneling predictions down to 2 K.