Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

Abstract

The quantum spin Hall insulator is characterized by a bandgap in the two-dimensional (2D) interior and helical 1D edge states1,2,3. Inducing superconductivity in the helical edge state results in a 1D topological superconductor, a highly sought-after state of matter at the core of many proposals for topological quantum computing4. In the present study, we report the coexistence of superconductivity and the quantum spin Hall edge state in a van der Waals heterostructure, by placing a monolayer of 1T′-WTe2, a quantum spin Hall insulator1,2,3, on a van der Waals superconductor, NbSe2. Using scanning tunnelling microscopy and spectroscopy (STM/STS), we demonstrate that the WTe2 monolayer exhibits a proximity-induced superconducting gap due to the underlying superconductor and that the spectroscopic features of the quantum spin Hall edge state remain intact. Taken together, these observations provide conclusive evidence for proximity-induced superconductivity in the quantum spin Hall edge state in WTe2, a crucial step towards realizing 1D topological superconductivity and Majorana bound states in this van der Waals material platform.

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Fig. 1: Fabrication and morphology of the WTe2/NbSe2 heterostructure.
Fig. 2: Simultaneous presence of the quantum spin Hall edge state and superconducting gap on monolayer WTe2.
Fig. 3: Evolution of the superconducting gap with WTe2 thickness at 4.7 K.
Fig. 4: Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2 at 2.8 K.

Data availability

The data represented Figs. 1, 2, 3 and 4 are available as Source Data with the online version of the paper. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank D. Xiao, D. Cobden and X. Xu for helpful discussions and N. Speeney and N. Iskos for assistance in the laboratory. B.M.H. was supported by the Department of Energy under the Early Career award programme (DE-SC0018115). Crystal growth and characterization at ORNL were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering. We thank the Pennsylvania State University Two-Dimensional Crystal Consortium—Materials Innovation Platform (2DCC-MIP), which is supported by NSF DMR-1539916, for supplying further 2D materials. F.L. and D.W. were supported by the NSF DMR-1809145 for STM measurements. We acknowledge NSF DMR-1626099 for acquisition of the STM instrument. S.C.d.l.B. was supported by the Department of Energy (DE-SC0018115) for fabrication of proximity-effect van der Waals heterostructures. Density functional theory calculations were supported by the Department of Energy under grant no. DE-SC0014506.

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Contributions

F.L., D.W., R.M.F. and B.M.H. designed the experiment. F.L. and D.W. acquired the experimental data and F.L., D.W. and R.M.F. analysed it. F.L., D.W. and S.C.d.l.B. fabricated the samples. F.L., D.W., S.C.d.l.B., R.M.F. and B.M.H. wrote the manuscript, and all authors commented on it. J.Y. grew the WTe2 crystals. D.G.M. provided other van der Waals crystals used in this study. M.W. performed density functional theory calculations. R.M.F. and B.M.H. supervised the project.

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Correspondence to Benjamin M. Hunt.

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Peer review information Nature Physics thanks Feng Miao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–8, Discussion and Table 1.

Source data

Source Data Fig. 1

Experimental source data.

Source Data Fig. 2

Experimental source data.

Source Data Fig. 3

Experimental and theoretical source data.

Source Data Fig. 4

Experimental and theoretical source data.

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Lüpke, F., Waters, D., de la Barrera, S.C. et al. Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2. Nat. Phys. 16, 526–530 (2020). https://doi.org/10.1038/s41567-020-0816-x

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