Published in Nature Physics 16, 526 (2020).
Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2
Felix Lüpke1, Dacen Waters1, Sergio C. de la Barrera1, Michael Widom1, David
G. Mandrus2,3,4, Jiaqiang Yan2, Randall M. Feenstra1, and Benjamin M. Hunt11
1Dept. Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
2Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
3Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA
4Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
Abstract
The quantum spin Hall (QSH) state was recently
demonstrated in monolayers of the transition metal
dichalcogenide 1T’-WTe2 and is characterized by a band
gap in the two-dimensional (2D) interior and helical one-dimensional
(1D) edge states [1–3]. Inducing superconductivity
in the helical edge states would result in a 1D
topological superconductor, a highly sought-after state
of matter [4]. In the present study, we use a novel
dry-transfer flip technique to place atomically-thin layers
of WTe2 on a van der Waals superconductor, NbSe2.
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 WTe2 for thicknesses from a monolayer
up to 7 crystalline layers. At the edge of the WTe2
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 WTe2, a crucial step
towards realizing 1D topological superconductivity in this
van der Waals material platform.
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