Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

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

Nature Physics volume 16, pages 526–530 (2020)Cite this article

Subjects

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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

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.

Similar content being viewed by others

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.

References

  1. Tang, S. et al. Quantum spin Hall state in monolayer 1T2-WTe2. Nat. Phys. 13, 683–687 (2017).

    Article  Google Scholar 

  2. Fei, Z. et al. Edge conduction in monolayer WTe2. Nat. Phys. 13, 677–682 (2017).

    Article  Google Scholar 

  3. Wu, S. et al. Observation of the quantum spin Hall effect up to 100 kelvin in a monolayer crystal. Science 359, 76–79 (2018).

    Article  ADS  MathSciNet  Google Scholar 

  4. Alicea, J. New directions in the pursuit of majorana fermions in solid state systems. Rep. Prog. Phys. 75, 076501 (2012).

    Article  ADS  Google Scholar 

  5. Kitaev, A. Y. Unpaired majorana fermions in quantum wires. Phys. Uspekhi 44, 131–136 (2001).

    Article  ADS  Google Scholar 

  6. Fu, L. & Kane, C. L. Superconducting proximity effect and majorana fermions at the surface of a topological insulator. Phys. Rev. Lett. 100, 096407 (2008).

    Article  ADS  Google Scholar 

  7. DasSarma, S., Freedman, M. & Nayak, C. Majorana zero modes and topological quantum computation. npj Quantum Inf. 1, 15001 (2015).

    Article  ADS  Google Scholar 

  8. Sato, M. & Ando, Y. Majorana zero modes and topological quantum computation. Rep. Prog. Phys. 80, 076501 (2017).

    Article  ADS  Google Scholar 

  9. Maeno, Y., Kittaka, S., Nomura, T., Yonezawa, S. & Ishida, K. Evaluation of spin-triplet superconductivity in Sr2 RuO4. J. Phys. Soc. Jpn 81, 011009 (2012).

    Article  ADS  Google Scholar 

  10. Fu, L. & Kane, C. L. Josephson current and noise at a superconductor/quantum-spin-Hall-insulator/superconductor junction. Phys. Rev. B 79, 161408 (2009).

    Article  ADS  Google Scholar 

  11. Wang, M.-X. et al. The coexistence of superconductivity and topological order in the Bi2Se3 thin films. Science 336, 52–55 (2012).

    Article  ADS  Google Scholar 

  12. Sun, H.-H. et al. Majorana zero mode detected with spin selective Andreev reflection in the vortex of a topological superconductor. Phys. Rev. Lett. 116, 257003 (2016).

    Article  ADS  Google Scholar 

  13. Hart, S. et al. Induced superconductivity in the quantum spin Hall edge. Nat. Phys. 10, 638–643 (2014).

    Article  Google Scholar 

  14. Bocquillon, E. et al. Gapless Andreev bound states in the quantum spin Hall insulator HgTe. Nat. Nanotechnol. 12, 137–143 (2016).

    Article  ADS  Google Scholar 

  15. Jia, Z.-Y. et al. Direct visualization of a two-dimensional topological insulator in the single-layer 1T2-WTe2. Phys. Rev. B 96, 041108 (2017).

    Article  ADS  Google Scholar 

  16. Peng, L. et al. Observation of topological states residing at step edges of WTe2. Nat. Commun. 8, 659 (2017).

    Article  ADS  Google Scholar 

  17. Shi, Y. et al. Imaging quantum spin Hall edges in monolayer WTe2. Sci. Adv. 5, eaat8799 (2019).

    Article  ADS  Google Scholar 

  18. Qian, X., Liu, J., Fu, L. & Li, J. Quantum spin Hall effect in two-dimensional transition metal dichalcogenides. Science 346, 1344–1347 (2014).

    Article  ADS  Google Scholar 

  19. Fatemi, V. et al. Electrically tunable low-density superconductivity in a monolayer topological insulator. Science 362, 926–929 (2018).

    Article  ADS  MathSciNet  Google Scholar 

  20. Sajadi, E. et al. Gate-induced superconductivity in a monolayer topological insulator. Science 362, 922–925 (2018).

    Article  ADS  Google Scholar 

  21. Zeng, Y. et al. High-quality magnetotransport in graphene using the edge-free Corbino geometry. Phys. Rev. Lett. 122, 137701 (2019).

    Article  ADS  Google Scholar 

  22. Cucchi, I. et al. Microfocus laser angle-resolved photoemission on encapsulated mono-, bi- and few-layer 1T2-WTe2. Nano Lett. 19, 554–560 (2019).

    Article  ADS  Google Scholar 

  23. Garoche, P., Veyssié, J. J., Manuel, P. & Molinié, P. Experimental investigation of superconductivity in 2H-NbSe2 single crystal. Solid State Commun. 19, 455–460 (1976).

    Article  ADS  Google Scholar 

  24. Huang, C. et al. Inducing strong superconductivity in WTe2 by a proximity effect. ACS Nano 12, 7185–7196 (2018).

    Article  Google Scholar 

  25. Li, Q. et al. Proximity-induced superconductivity with subgap anomaly in type II Weyl semi-metal WTe2. Nano Lett. 18, 7962–7968 (2018).

    Article  ADS  Google Scholar 

  26. Reeg, C. R. & Maslov, D. L. Hard gap in a normal layer coupled to a superconductor. Phys. Rev. B 94, 020501 (2016).

    Article  ADS  Google Scholar 

  27. Jäck, B. et al. Observation of a Majorana zero mode in a topologically protected edge channel. Science 364, 1255–1259 (2019).

    Article  ADS  Google Scholar 

  28. Khestanova, E. et al. Unusual suppression of the superconducting energy gap and critical temperature in atomically thin NbSe2. Nano Lett. 18, 2623–2629 (2018).

    Article  ADS  Google Scholar 

  29. Li, G., Luican, A. & Andrei, E. Y. Self-navigation of a scanning tunneling microscope tip toward a micron-sized graphene sample. Rev. Sci. Instrum. 82, 073701 (2011).

    Article  ADS  Google Scholar 

Download references

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.

Author information

Author notes

  1. Felix Lüpke

    Present address: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA

  2. These authors contributed equally: Felix Lüpke, Dacen Waters.

Authors and Affiliations

  1. Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA

    Felix Lüpke, Dacen Waters, Sergio C. de la Barrera, Michael Widom, Randall M. Feenstra & Benjamin M. Hunt

  2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

    David G. Mandrus & Jiaqiang Yan

  3. Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA

    David G. Mandrus

  4. Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA

    David G. Mandrus

Authors
  1. Felix Lüpke
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Dacen Waters
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Sergio C. de la Barrera
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Michael Widom
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. David G. Mandrus
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Jiaqiang Yan
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Randall M. Feenstra
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Benjamin M. Hunt
    View author publications

    You can also search for this author in PubMed Google Scholar

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.

Corresponding author

Correspondence to Benjamin M. Hunt.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

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

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

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

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41567-020-0816-x

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing