Parity-Affected Persistent Currents in Superconducting Nanorings

TL;DR

This paper explores how the superconducting parity effect influences persistent currents in nanorings, predicting phenomena like parity-induced blocking and spontaneous supercurrents without external flux at low temperatures.

Contribution

It introduces the concept that superconducting parity can significantly alter persistent currents, including novel effects like parity-induced blocking and spontaneous supercurrents in nanorings.

Findings

Parity effect can block persistent currents in quantum point contacts.

Odd electron number induces a $$-state in SNS junctions.

Spontaneous supercurrents occur without external magnetic flux.

Abstract

We argue that at sufficiently low temperatures T superconducting parity effect may strongly influence equilibrium persistent currents (PC) in isolated superconducting nanorings containing a weak link with few conducting modes. For a single channel quantum point contact at T=0 we predict a novel effect of parity-induced blocking of PC. 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.