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Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures

Nature Materials volume 22, pages 570–575 (2023)Cite this article

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Abstract

The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana zero modes1,2. The development of a scalable material platform is key to the realization of topological quantum computing3,4. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5–10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.

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Fig. 1: Epitaxial growth of BST/Gr/Ga heterostructures and fabrication of tunnel junction devices.
Fig. 2: Coexistence of Dirac surface states and superconductivity in BST/Gr/Ga heterostructures.
Fig. 3: Proximity-induced superconductivity in BST/Gr/Ga heterostructures.
Fig. 4: Evidence of vortex trapping and single vortex signature in tunnelling conductance.

Data availability

The data needed to reproduce the figures in the main text and Supplementary Information are available on Zenodo (https://doi.org/10.5281/zenodo.7485214).

Code availability

The codes used in the theoretical simulations and calculations are available from the corresponding author upon reasonable request.

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Acknowledgements

C.L., H.Y., C.-Z.C., S.K., T.B., J.L.T, J.A.R., D.R.H and J.Z. are supported by the Penn State Materials Research Science and Engineering Center for Nanoscale Science (DMR-2011839). Y.-F.Z, Z.Y. and C.-Z.C. are supported by the National Science Foundation CAREER award (DMR-1847811) and Gordon and Betty Moore Foundation’s EPiQS Initiative (GBMF9063 to C.-Z.C.). C.D. and J.A.R. are supported by the Penn State National Science Foundation Materials Innovation Platforms Two-Dimensional Crystal Consortium award (DMR-1539916). A.V. and J.A.R. are supported by the National Science Foundation (DMR 2002651). O.L. and Y.O. are supported by the US–Israel Binational Science Foundation and National Science Foundation (2018643), the European Union’s Horizon 2020 research and innovation programme (grant agreement LEGOTOP no. 788715), the DFG German Research Foundation (CRC/Transregio 183, EI 519/7-1) and ISF Quantum Science and Technology (2074/19). K. Watanabe and T.T. acknowledge support from the Japan Society for the Promotion of Science KAKENHI (grant numbers 19H05790, 20H00354 and 21H05233). J.L.T. and D.R.H. thank the Penn State Eberly College of Science, Department of Chemistry and Materials Research Institute for generous support through start-up funds. The coauthors acknowledge use of the Penn State Materials Characterization Lab. We thank C.-X. Liu, R. Mei and Y. Liu for helpful discussions and R. Zhang and F. Turker for assistance in measurement.

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Authors and Affiliations

  1. Department of Physics, The Pennsylvania State University, University Park, PA, USA

    Cequn Li, Yi-Fan Zhao, Hemian Yi, Zijie Yan, Joshua A. Robinson, Cui-Zu Chang & Jun Zhu

  2. Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, USA

    Alexander Vera, Shalini Kumari, Timothy Bowen, Joshua A. Robinson & Jun Zhu

  3. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA

    Alexander Vera, Shalini Kumari, Timothy Bowen, Danielle Reifsnyder Hickey & Joshua A. Robinson

  4. Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel

    Omri Lesser & Yuval Oreg

  5. 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USA

    Chengye Dong, Joshua A. Robinson & Jun Zhu

  6. Materials Research Institute, The Pennsylvania State University, University Park, PA, USA

    Ke Wang, Haiying Wang, Danielle Reifsnyder Hickey & Joshua A. Robinson

  7. Department of Chemistry, The Pennsylvania State University, University Park, PA, USA

    Jessica L. Thompson, Danielle Reifsnyder Hickey & Joshua A. Robinson

  8. Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan

    Kenji Watanabe

  9. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan

    Takashi Taniguchi

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  1. Cequn Li
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Contributions

C.L. and J.Z. designed the experiment. C.L. fabricated the devices and made the transport measurements under the supervision of J.Z.; Y.-F.Z., H.Y. and Z.Y. performed the MBE growth and ARPES measurements under the supervision of C.-Z.C.; A.V., S.K., C.D. and T.B. performed the CHet growth and characterizations under the supervision of J.A.R.; O.L. performed BTK modelling under the supervision of Y.O.; K. Watanabe and T.T. synthesized the h-BN crystals; K. Wang, H.W. and J.L.T. under the supervision of D.R.H. performed the focused ion beam and transmission electron microscopy measurements; C.L. and J.Z. analysed the data; and C.L. and J.Z. wrote the manuscript with input from all authors.

Corresponding author

Correspondence to Jun Zhu.

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Supplementary Figs. 1–8, Tables 1 and 2 and Discussion.

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Li, C., Zhao, YF., Vera, A. et al. Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures. Nat. Mater. 22, 570–575 (2023). https://doi.org/10.1038/s41563-023-01478-4

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