Some novel effects in superconducting nanojunctions

TL;DR

This paper explores new theoretical effects in superconducting nanojunctions, including quantum interference, Andreev reflection, and parity effects, revealing how they can qualitatively alter Josephson currents and induce spontaneous supercurrents.

Contribution

It introduces novel theoretical insights into the interplay of quantum interference, Andreev reflection, and parity effects in superconducting nanojunctions and rings.

Findings

Quantum interference and Andreev reflection can qualitatively modify Josephson current.

Parity effects can suppress supercurrent in nanorings with odd electron numbers.

Spontaneous supercurrents can occur without external magnetic flux in certain superconducting rings.

Abstract

In this paper we address several new developments in the theory of dc Josephson effect in superconducting weak links. We analyze an interplay between quantum interference effects and Andreev reflection in SNS nanojunctions with insulating barriers and demonstrate that such effects may qualitatively modify the Josephson current in such structures. We also investigate an impact of the parity effect on persistent currents in superconducting nanorings interrupted by a quantum point contact (QPC). In the limit of zero temperature and for the odd number of electrons in the ring we predict complete suppression of the supercurrent across QPC with one conducting mode. In nanorings with SNS junctions a $\pi$-state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux.