Unveiling Topological Hinge States in the Higher-Order Topological Insulator WTe$_2$ Based on the Fractional Josephson Effect

TL;DR

This paper demonstrates the topological nature of hinge states in WTe$_2$ HOTIs through microwave-induced Shapiro step analysis, revealing 4π-periodic Josephson effects indicative of topological superconductivity.

Contribution

It provides experimental evidence of topological hinge states in WTe$_2$ HOTIs using microwave measurements of Josephson junctions, highlighting their potential for topological quantum applications.

Findings

Absence of the first Shapiro step in hinge-dominated JJs

Observation of 4π-periodic current-phase relationship

Implications for topological superconductivity and Majorana modes

Abstract

Higher-order topological insulators (HOTIs) represent a novel class of topological materials, characterised by the emergence of topological boundary modes at dimensions two or more lower than those of bulk materials. Recent experimental studies have identified conducting channels at the hinges of HOTIs, although their topological nature remains unexplored. In this study, we investigated Shapiro steps in Al-WTe$_2$-Al proximity Josephson junctions (JJs) under microwave irradiation and examined the topological properties of the hinge states in WTe$_2$. Specifically, we analysed the microwave frequency dependence of the absence of the first Shapiro step in hinge-dominated JJs, attributing this phenomenon to the 4$\pi$-periodic current-phase relationship characteristic of topological JJs. These findings may encourage further research into topological superconductivity with topological hinge states in superconducting hybrid devices based on HOTIs. Such advances could lead to the realisation of Majorana zero modes for topological quantum physics and pave the way for applications in spintronic devices.