One-Dimensional Edge Transport in Few-Layer WTe$_2$

Abstract

WTe 2 is a layered transitional metal dichalcogenide (TMD) with a number of intriguing topological properties. The bulk crystal is a Weyl semimetal with Fermi arc surface states and the monolayer is a two-dimensional (2D) topological insulator. Recently, WTe 2 has also been predicted to be a higher-order topological insulator (HOTI) with hinge states along the edges. The gapless nature of WTe 2 complicates the observation of one-dimensional (1D) topological states in transport due to their small contribution relative to the bulk. Here, the Josephson effect can help to detect the edge transport, since the evolution of the critical current in magnetic field is sensitive to the spatial current distribution. Here, we employ superconducting contacts in WTe 2 that emerge when Pd is placed in contact with the TMD to define Josephson junctions. Using the Josephson effect, we demonstrate the presence of 1D current carrying states residing on the edges and steps of few-layer WTe 2 crystals. The width of the 1D current-carrying states is deduced to be below 80 nm. A supercurrent I c is measured over distances up to 3 µm and persisting in magnetic fields up to B = 2 T. This observation is in good agreement with the recent prediction of HOTI states in WTe 2 . Moreover, the observed dependencies of I c (B) on magnetic field demonstrate a particular symmetry with the direction of the current and the magnetic field, which matches the prediction for topological states in systems with broken inversion symmetry. Our observation adds another effect to a plethora of intriguing properties of WTe 2 and potentially provides a new platform for obtaining Majorana zero modes.