Quantum interference in topological insulator Josephson junctions

TL;DR

This paper numerically investigates how topological insulator edge states exhibit proximity-induced superconductivity in Josephson junctions, revealing size-dependent effects and clarifying the role of bulk states in interference patterns.

Contribution

It demonstrates through numerical simulations that edge states in topological insulators show enhanced proximity effects and clarifies the influence of residual bulk states on superconducting interference.

Findings

Proximity-induced superconductivity observed in edge states.

Bulk states can cause measurable resistance but have minimal impact on interference.

Size effects influence the visibility of bulk states in superconducting interference.

Abstract

Using non-equilibrium Green's functions, we studied numerically the transport properties of a Josephson junction, superconductor-topological insulator-superconductor hybrid system. Our numerical calculation shows first that proximity-induced superconductivity is indeed observed in the edge states of a topological insulator adjoining two superconducting leads and second that the special characteristics of topological insulators endow the edge states with an enhanced proximity effect with a superconductor but do not forbid the bulk states to do the same. In a size-dependent analysis of the local current, it was found that a few residual bulk states can lead to measurable resistance, whereas because these bulk states spread over the whole sample, their contribution to the interference pattern is insignificant when the sample size is in the micrometer range. Based on these numerical results, it is concluded that the apparent disappearance of residual bulk states in the superconducting interference process as described in Ref. [\onlinecite{HartNautrePhys2014f}] is just due to the effects of size: the contribution of the topological edge states outweighs that of the residual bulk states.