Relating Andreev Bound States and Supercurrents in Hybrid Josephson Junctions

TL;DR

This paper explores the relationship between Andreev bound states and supercurrents in hybrid Josephson junctions, demonstrating how the bound state spectrum can predict supercurrent behavior in superconducting quantum interference devices.

Contribution

It introduces a novel device design that enables independent measurement of Andreev bound states and supercurrents, revealing their direct relationship in epitaxial InAs/Al heterostructures.

Findings

Andreev bound state spectrum can predict supercurrent.

Critical current measurements average out energy spectrum details.

Field-dependent spectrum and supercurrent depend on second junction and kinetic inductance.

Abstract

We investigate superconducting quantum interference devices consisting of two highly transmissive Josephson junctions coupled by a superconducting loop, all defined in an epitaxial InAs/Al heterostructure. A novel device design allows for independent measurements of the Andreev bound state spectrum within the normal region of a junction and the resulting current-phase relation. We show that knowledge of the Andreev bound state spectrum alone is enough to derive the independently measured phase dependent supercurrent. On the other hand, the opposite relation does not generally hold true as details of the energy spectrum are averaged out in a critical current measurement. Finally, quantitative understanding of field dependent spectrum and supercurrent require taking into account the second junction in the loop and the kinetic inductance of the epitaxial Al film.