Effect of ac Impedance on dc Voltage-Current Characteristics of Superconductor Weak-Link Junctions

TLDR

The ac impedance seen by a weak‑link superconductor junction influences both its response time to bias changes and its dc voltage‑current characteristics, a second effect that has not been widely recognized but is important for device design. The authors analyze two illustrative cases—ac capacitive and inductive loading—to elucidate the underlying principles. These analyses partly explain the observed differences in dc voltage‑current characteristics between plane‑parallel and point‑contact junctions.

Abstract

Because the Josephson pair current in a weak-link superconductor junction is a nonlinear parametric function of junction voltage, the ac impedance seen by the junction influences both the response time to changes in bias and the dc voltage-current characteristics. The first effect is obvious; the second, considered here, has not been generally recognized. Both are relevant to device design. Two special cases which illustrate the basic principles involved are worked out in detail; they correspond, respectively, to ac capacitive and inductive loading. The results partly explain differences in the dc voltage-current characteristics of plane-parallel and point-contact junctions.