Current-carrying states in superconductor/insulator and superconductor/semiconductor superlattices in the mesoscopic regime

TL;DR

This paper explores the theoretical behavior of current-carrying states in mesoscopic superconductor/insulator and superconductor/semiconductor superlattices, focusing on Josephson effects, critical currents, and the influence of exchange interactions.

Contribution

It provides analytical expressions for the Josephson critical current and examines how supercurrent affects superconductivity and critical temperature in mesoscopic superlattices.

Findings

Critical Josephson current depends on temperature with unusual behavior.

Supercurrent can exponentially suppress the superconducting gap.

Exchange interactions significantly lower the critical temperature.

Abstract

We discuss some of the basic theoretical aspects of current-carrying states in superconducting superlattices with tunnel barriers in the mesoscopic regime, when the superconducting layer thickness is small compared to the BCS coherence length but large compared to the atomic scale. We establish the necessary conditions for the observation of the classical Josephson effect (with sinusoidal current-phase dependence) and derive self-consistent analytical expressions for the critical Josephson current. These expressions are proportional to an additional small factor and have unusual temperature dependence as compared with the single-junction case. For certain parameter values, the superconducting gap exhibits an exponential decrease due to pair-breaking effect of the supercurrent. The supercurrent can completely destroy the superconductivity of the system above a certain characteristic temperature (lower than the transition temperature of individual layers). In this paper, we also study the effect of intrabarrier exchange interactions. We show that this effect is strongly enhanced compared with the single- junction case and can manifest itself in an exponential decrease of the critical temperature.