Trimming the critical current of Josephson junctions

We have demonstrated the feasibility of trimming the critical current of Josephson tunnel junctions by doping the lead alloy counter electrodes. The critical current may be changed by more than a factor of six, while retaining the quality of the current-voltage characteristics and the critical current uniformity. For junctions with PbSb counter electrodes doped with less than 0.2 nm of Sn, the increase of critical current is stable after proper annealing and depends linearly on the dosage. For dosages heavier than 0.25 nm, the increase of critical current saturates at ∼ 500%. These changes may be explained by the conversion of some oxide at the interface between the counter electrode and the tunneling barrier to the oxide of the dopant. The modification of the height and thickness of the tunneling barrier changes the critical current of the junction.