Microscopic model for multiple flux transitions in mesoscopic superconducting loops

TL;DR

This paper develops a microscopic model explaining multiple flux quantum transitions in mesoscopic superconducting loops, highlighting the role of metastable states and the influence of persistent currents and non-equilibrium quasiparticles.

Contribution

It introduces a novel microscopic framework that accounts for multiple flux transitions and the effects of metastable states in superconducting rings with tunnel junctions.

Findings

Multiple flux quantum transitions are explained by metastable states with large vorticity.

Persistent currents modulate the superconducting density of states and tunnel current.

Non-equilibrium quasiparticles may affect the stability of metastable states.

Abstract

A microscopic model is constructed which is able to describe multiple magnetic flux transitions as observed in recent ultra-low temperature tunnel experiments on an aluminum superconducting ring with normal metal - insulator - superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual multiple flux quantum transitions are explained by the formation of metastable states with large vorticity. Essential in our description is the modification of the pairing potential and the superconducting density of states by a sub-critical value of the persistent current which modulates the measured tunnel current. We also speculate on the importance of the injected non-equilibrium quasiparticles on the stability of these metastable states.