Keldysh study of point-contact tunneling between superconductors

TL;DR

This paper develops a theoretical framework using the Keldysh Green function formalism to analyze tunneling in superconducting point contacts, considering various pairing symmetries, magnetic fields, and temperatures, with implications for experimental measurements.

Contribution

It introduces a simplified method for calculating current-voltage characteristics in superconducting junctions with diverse pairing symmetries and external conditions, extending previous models.

Findings

Effects of pairing symmetry and magnetic fields on tunneling currents

Proposed experimental methods for detecting non-standard superconducting states

Relevance to organic superconductors and ruthenium compounds

Abstract

We revisit the problem of point-contact tunnel junctions involving one-dimensional superconductors and present a simple scheme for computing the full current-voltage characteristics within the framework of the non-equilibrium Keldysh Green function formalism. We address the effects of different pairing symmetries combined with magnetic fields and finite temperatures at arbitrary bias voltages. We discuss extensively the importance of these results for present-day experiments. In particular, we propose ways of measuring the effects found when the two sides of the junction have dissimilar superconducting gaps and when the symmetry of the superconducting states is not the one of spin-singlet pairing. This last point is of relevance for the study of the superconducting state of certain organic materials like the Bechgaard salts and, to some extent, for ruthenium compounds.