Fluctuations of the Josephson current and electron-electron interactions in superconducting weak links

TL;DR

This paper develops a microscopic theory for superconducting weak links with arbitrary transmission, revealing new fluctuation and interaction effects due to subgap states, and analyzing supercurrent noise and Coulomb corrections.

Contribution

It introduces a formalism that describes fluctuations and interactions in superconducting contacts beyond the tunneling limit, accounting for subgap Andreev bound states.

Findings

Interaction correction vanishes at T=0 for fully transparent contacts.

New fluctuation features due to subgap Andreev states.

Supercurrent noise analyzed in the presence of electron-electron interactions.

Abstract

We derive a microscopic effective action for superconducting contacts with arbitrary transmission distribution of conducting channels. Provided fluctuations of the Josephson phase remain sufficiently small our formalism allows to fully describe fluctuation and interaction effects in such systems. As compared to the well studied tunneling limit our analysis yields a number of qualitatively new features which occur due to the presence of subgap Andreev bound states in the system. We investigate the equilibrium supercurrent noise and evaluate the electron-electron interaction correction to the Josephson current across superconducting contacts. At T=0 this correction is found to vanish for fully transparent contacts indicating the absence of Coulomb effects in this limit.