Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe${}_2$

Abstract

The quantum spin Hall (QSH) state was recently demonstrated in monolayers of the transition metal dichalcogenide 1T'-WTe${}_2$ and is characterized by a band gap in the two-dimensional (2D) interior and helical one-dimensional (1D) edge states. Inducing superconductivity in the helical edge states would result in a 1D topological superconductor, a highly sought-after state of matter. In the present study, we use a novel dry-transfer flip technique to place atomically-thin layers of WTe${}_2$ on a van der Waals superconductor, NbSe${}_2$. Using scanning tunneling microscopy and spectroscopy (STM/STS), we demonstrate atomically clean surfaces and interfaces and the presence of a proximity-induced superconducting gap in the WTe${}_2$ for thicknesses from a monolayer up to 7 crystalline layers. At the edge of the WTe${}_2$ monolayer, we show that the superconducting gap coexists with the characteristic spectroscopic signature of the QSH edge state. Taken together, these observations provide conclusive evidence for proximity-induced superconductivity in the QSH edge state in WTe${}_2$, a crucial step towards realizing 1D topological superconductivity and Majorana bound states in this van der Waals material platform.

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• Role of interface hybridization on induced superconductivity in 1T${}^{\prime }$-WTe${}_2$ and 2H-NbSe${}_2$ heterostructures
• Electronic properties of the steps in bilayer Td-WTe2
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