Long-lived Andreev states as evidence for protected hinge modes in a bismuth nanoring Josephson junction

TL;DR

This paper provides experimental evidence for protected hinge modes in a bismuth nanoring Josephson junction by analyzing supercurrent statistics, revealing the spatial separation of topological helical states through unique relaxation dynamics.

Contribution

It demonstrates the presence of helical Andreev hinge states in a bismuth nanoring, offering new insights into second-order topological insulators and their superconducting properties.

Findings

Pairs relax at a rate similar to quasiparticles, unlike non-topological systems.

Evidence of spatial separation of topological helical hinge states.

Supercurrent statistics reveal protected hinge modes.

Abstract

Second-order topological insulators are characterized by helical, non-spin-degenerate, one-dimensional states running along opposite crystal hinges, with no backscattering. Injecting superconducting pairs therefore entails splitting Cooper pairs into two families of helical Andreev states of opposite helicity, one at each hinge. Here we provide evidence for such separation via the measurement and analysis of switching supercurrent statistics of a crystalline nanoring of bismuth. Using a phenomenological model of two helical Andreev hinge modes, we find that pairs relax at a rate comparable to individual quasiparticles, in contrast with the much faster pair relaxation of non-topological systems. This constitutes a unique tell-tale sign of the spatial separation of topological helical hinges.