Probing the topological protection of edge states in multilayer tungsten ditelluride with the superconducting proximity effect

The topology of WTe2, a transition metal dichalcogenide with large spin-orbit interactions, is thought to combine type II Weyl semimetal and second-order topological insulator (SOTI) character. The SOTI character should endow WTe2 multilayer crystals with topologically protected helical states at its hinges, and, indeed, 1D states have been detected thanks to Josephson interferometry. However, the immunity to backscattering conferred to those states by their helical nature has so far not been tested. To probe the topological protection of WTe2 edge states, we have fabricated Superconducting Quantum Interference Devices (SQUIDs) in which the supercurrent through a junction on the crystal edge interferes with the supercurrent through a junction in the bulk of the crystal. We find behaviors ranging from a Symmetric SQUID pattern to asymmetric SQUID patterns, including one in which the modulation by magnetic field reveals a sawtooth-like supercurrent versus phase relation for the edge junction, demonstrating that the supercurrent at the edge is carried by ballistic channels over 600 nm, a tell-tale sign of the SOTI character of WTe2.