Giant anomalous Josephson effect as a probe of spin texture in topological insulators

TL;DR

This study demonstrates that the giant anomalous Josephson effect in HgTe nanowire junctions can be used as a sensitive probe of spin texture, revealing deviations from perfect perpendicularity between spin and momentum.

Contribution

It provides experimental evidence of a giant $$-shift in the Josephson current-phase relation and uses this effect to analyze the spin texture in topological insulator surface states.

Findings

Giant anomalous $$-shift observed in HgTe nanowire junctions

Spin deviates by 19 degrees from perpendicular to momentum

Anomalous Josephson effect as a tool to probe spin texture

Abstract

Surface states of topological insulators feature chiral spin-momentum locking. When such states are used as weak link between two superconductors, their spin texture gives rise to the anomalous Josephson effect, i.e., to a $\varphi_0$ shift in the current phase relation. In this work, we explore the anomalous Josephson effect in junctions where the weak link is a HgTe nanowire. We observe a giant anomalous $\varphi_0$-shift of the current-phase relation, which we attribute to the fact that HgTe surface states feature a single Fermi contour. Moreover, by varying the orientation of the in-plane magnetic field, we obtain information about the spin texture in momentum space. In particular, we found that the spin is not exactly perpendicular to the momentum, but shows a significant deviation of 19 degrees. Our results establish the anomalous Josephson effect as a sensitive tool to probe the spin texture of chiral 2D systems.