Fate of the Josephson effect in thin-film superconductors

TL;DR

This paper investigates the fate of the Josephson effect in thin-film superconductors, revealing its absence at nonzero temperature and a universal, thermally activated resistance behavior influenced by film properties.

Contribution

It provides a theoretical analysis showing the suppression of the Josephson effect in thin films at finite temperature and identifies a universal energy barrier affecting contact resistance.

Findings

Josephson effect is absent at nonzero temperature in thin films.

Contact resistance varies with temperature in a nearly activated manner.

Universal energy barrier depends on superfluid stiffness and geometry.

Abstract

The dc Josephson effect refers to the dissipationless electrical current -- the supercurrent -- that can be sustained across a weak link connecting two bulk superconductors. This effect is a probe of the fundamental nature of the superconducting state. Here, we analyze the case of two superconducting thin films connected by a point contact. Remarkably, the Josephson effect is absent at nonzero temperature, and the resistance across the contact is nonzero. Moreover, the point contact resistance is found to vary with temperature in a nearly activated fashion, with a UNIVERSAL energy barrier determined only by the superfluid stiffness characterizing the films, an angle characterizing the geometry, and whether or not the Coulomb interaction between Cooper pairs is screened. This behavior reflects the subtle nature of the superconductivity in two-dimensional thin films, and should be testable in detail by future experiments.