Lead alloy Josephson junctions with Pb-Bi counterelectrodes

Abstract

An experimental investigation has indicated that the ε‐phase Pb‐Bi alloy is an attractive alternative to Pb–1.7 wt.% Au for use as a counterelectrode for Josephson tunneling devices containing Pb–12 wt.% In–4 wt.% Au alloy films as base electrodes and control lines. Use of this Pb‐Bi alloy as a counterelectrode results in a significant improvement in junction quality; the normalized subgap single‐particle tunneling current is ∼2× lower at 2 mV. In addition, devices with the Pb‐Bi counterelectrodes exhibit ∼3× fewer failures after repeated thermal cycling between 300 and 4.2 °K. Out ot a total of 72 such devices having large area (6.2×10⁻⁶ cm²) junctions, 94% survived 1000 thermal cycles with negligible change.