WTe2 is a layered transitional-metal dichalcogenide (TMD) with a number of intriguing topological properties. Recently, WTe2 has been predicted to be a higher-order topological insulator (HOTI) with topologically protected hinge states along the edges. The gapless nature of WTe2 complicates the observation of one-dimensional (1D) topological states in transport due to their small contribution relative to the bulk. Here, we study the behavior of the Josephson effect in magnetic field to distinguish edge from bulk transport. The Josephson effect in few-layer WTe2 reveals 1D states residing on the edges and steps. Moreover, our data demonstrates a combination of Josephson transport properties observed solely in another HOTIbismuth, including Josephson transport over micrometer distances, extreme robustness in a magnetic field, and nonsinusoidal current-phase relation (CPR). Our observations strongly suggest the topological origin of the 1D states and that few-layer WTe2 is a HOTI.

We investigate electron transport through the interface between a niobium superconductor and the edge of a two-dimensional semimetal, realized in a 20 nm wide HgTe quantum well. Experimentally, we observe that typical behavior of a single Andreev contact is complicated by both a pronounced zero-bias resistance anomaly and shallow subgap resistance oscillations with 1/n periodicity. These results are demonstrated to be independent of the superconducting material and should be regarded as specific to a 2D semimetal in a proximity with a superconductor. We interpret these effects to originate from the Andreev-like correlated process at the edge of a two-dimensional semimetal.

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe2 Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe2 interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.

We experimentally investigate Andreev transport through the interface between an indium superconductor and the edge of the InAs/GaSb bilayer. To cover all possible regimes of InAs/GaSb spectrum, we study samples with 10-nm, 12 nm, and 14 nm thick InAs quantum wells. For the trivial case of a direct band insulator in 10 nm samples, differential resistance demonstrates standard Andreev reflection. For InAs/GaSb structures with band inversion (12 nm and 14 nm samples), we observe distinct low-energy structures, which we regard as direct evidence for the proximity-induced superconductivity within the current-carrying edge state. For 14 nm InAs well samples, we additionally observe mesoscopic-like resistance fluctuations, which are subjected to threshold suppression in low magnetic fields.