Identifying Majorana bound states at quantum spin Hall edges using a metallic probe

TL;DR

This paper demonstrates that conductance peaks at zero temperature in quantum spin Hall insulator systems with superconductors and ferromagnets can serve as signatures of Majorana bound states, providing a practical detection method.

Contribution

It introduces a robust conductance measurement technique using a metallic probe to identify Majorana bound states at QSHI edges, unaffected by probe distance or parameter variations.

Findings

A $2e^2/h$ conductance peak indicates a single MBS.

A $4e^2/h$ conductance peak signals a pair of MBSs.

Conductance peaks are stable over parameter changes and probe distances.

Abstract

We study the conductance afforded by a normal-metal probe which is directly contacting the helical edge modes of a quantum spin Hall insulator (QSHI). We show a $2e^2/h$ conductance peak at zero temperature in QSHI-based superconductor--ferromagnet hybrids due to the formation of a single Majorana bound state (MBS). In a corresponding Josephson junction hosting a pair of MBSs, a $4e^2/h$ conductance peak is found at zero temperature. The conductance quantization is robust to changes of the relevant system parameters and, remarkably, remains unaltered with increasing the distance between probe and MBSs. In the low temperature limit, the conductance peak is robust as the probe is placed within the localization length of MBSs. Our findings can therefore provide an effective way to detect the existence of MBSs in QSHI systems.