INVESTIGATION OF LOW-TEMPERATURE IV CURVES OF HIGH-QUALITY NB/AL-ALOX/NB JOSEPHSON-JUNCTIONS

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 congruent-to DELTA/e is observed. Comparison with the theoretical model for two-particle tunneling is performed, but a substantial disagreement is found. At V < DELTA/e the measured current is in remarkably good agreement with the single particle tunneling predictions down to 2 K.