Evidence of Higher Order Topology in Multilayer WTe$_2$ from Josephson Coupling through Anisotropic Hinge States

TL;DR

This study provides experimental evidence for higher order topological phases in multilayer WTe$_2$, revealing anisotropic hinge states through Josephson coupling measurements, advancing understanding of topological semimetals in superconducting heterostructures.

Contribution

First direct spatial detection of anisotropic hinge states in WTe$_2$ using Josephson junction interference, confirming higher order topological phases.

Findings

Enhanced Josephson current at edges along the a-axis indicates hinge states.

Hinge states are anisotropic, absent along the b-axis.

Results align with theoretical predictions of higher order topology.

Abstract

The noncentrosymmetric Td-WTe$_2$, previously known as a type-II Weyl semimetal, is expected to have higher order topological phases with topologically protected, helical one-dimensional (1D) hinge states when their scarcely separated Weyl points get annihilated. However, the detection of these hinge states is difficult in the presence of the semimetallic behaviour of the bulk. Here, we spatially resolved the hinge states by analysing the magnetic field interference of supercurrent in Nb-WTe$_2$-Nb proximity Josephson junctions. The Josephson current along the a-axis of the WTe$_2$ crystal, but not along the b-axis, showed sharp enhancements at the edges of the junction; the amount of enhanced Josephson current was comparable to the upper limits of a single 1D conduction channel. Our experimental observations provide evidence of the higher order topological phase in WTe$_2$ and its corresponding anisotropic topological hinge states, in good agreement with theoretical calculations. Our work paves the way for hinge transport studies on topological semimetals in superconducting heterostructures, including their topological superconductivity.