Reduced leakage current in Josephson tunnel junctions with codeposited barriers

TL;DR

This paper compares two fabrication methods for Josephson junctions, demonstrating that codeposited barriers significantly reduce leakage current and align with theoretical predictions, unlike thermally oxidized barriers.

Contribution

It introduces a codeposition technique for barrier formation in Josephson junctions, achieving lower leakage currents and better theoretical agreement.

Findings

Codeposited barriers show no measurable shunt conductance.

Thermally oxidized barriers exhibit small shunt conductance.

Codeposition yields junctions with predicted subgap current.

Abstract

Josephson junctions were fabricated using two different methods of barrier formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the first two layers were epitaxial. The oxide barrier was formed either by exposing the Al surface to O2 or by codepositing Al in an O2 background. The codeposition process yielded junctions that showed the theoretically predicted subgap current and no measurable shunt conductance. In contrast, devices with barriers formed by thermal oxidation showed a small shunt conductance in addition to the predicted subgap current.