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Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect

Author

Listed:
  • J. O. Island

    (University of California)

  • X. Cui

    (University of California)

  • C. Lewandowski

    (Massachusetts Institute of Technology)

  • J. Y. Khoo

    (Massachusetts Institute of Technology)

  • E. M. Spanton

    (University of California)

  • H. Zhou

    (University of California)

  • D. Rhodes

    (Columbia University)

  • J. C. Hone

    (Columbia University)

  • T. Taniguchi

    (National Institute for Materials Science)

  • K. Watanabe

    (National Institute for Materials Science)

  • L. S. Levitov

    (Massachusetts Institute of Technology)

  • M. P. Zaletel

    (University of California)

  • A. F. Young

    (University of California)

Abstract

Spin–orbit coupling (SOC) is the key to realizing time-reversal-invariant topological phases of matter1,2. SOC was predicted by Kane and Mele3 to stabilize a quantum spin Hall insulator; however, the weak intrinsic SOC in monolayer graphene4–7 has precluded experimental observation in this material. Here we exploit a layer-selective proximity effect—achieved via a van der Waals contact with a semiconducting transition-metal dichalcogenide8–21—to engineer Kane–Mele SOC in ultra clean bilayer graphene. Using high-resolution capacitance measurements to probe the bulk electronic compressibility, we find that SOC leads to the formation of a distinct, incompressible, gapped phase at charge neutrality. The experimental data agree quantitatively with a simple theoretical model in which the new phase results from SOC-driven band inversion. In contrast to Kane–Mele SOC in monolayer graphene, the inverted phase is not expected to be a time-reversal-invariant topological insulator, despite being separated from conventional band insulators by electric-field-tuned phase transitions where crystal symmetry mandates that the bulk gap must close22. Our electrical transport measurements reveal that the inverted phase has a conductivity of approximately e2/h (where e is the electron charge and h Planck’s constant), which is suppressed by exceptionally small in-plane magnetic fields. The high conductivity and anomalous magnetoresistance are consistent with theoretical models that predict helical edge states within the inverted phase that are protected from backscattering by an emergent spin symmetry that remains robust even for large Rashba SOC. Our results pave the way for proximity engineering of strong topological insulators as well as correlated quantum phases in the strong spin–orbit regime in graphene heterostructures.

Suggested Citation

  • J. O. Island & X. Cui & C. Lewandowski & J. Y. Khoo & E. M. Spanton & H. Zhou & D. Rhodes & J. C. Hone & T. Taniguchi & K. Watanabe & L. S. Levitov & M. P. Zaletel & A. F. Young, 2019. "Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect," Nature, Nature, vol. 571(7763), pages 85-89, July.
  • Handle: RePEc:nat:nature:v:571:y:2019:i:7763:d:10.1038_s41586-019-1304-2
    DOI: 10.1038/s41586-019-1304-2
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    Cited by:

    1. Lihuan Sun & Louk Rademaker & Diego Mauro & Alessandro Scarfato & Árpád Pásztor & Ignacio Gutiérrez-Lezama & Zhe Wang & Jose Martinez-Castro & Alberto F. Morpurgo & Christoph Renner, 2023. "Determining spin-orbit coupling in graphene by quasiparticle interference imaging," Nature Communications, Nature, vol. 14(1), pages 1-8, December.
    2. Qing Rao & Wun-Hao Kang & Hongxia Xue & Ziqing Ye & Xuemeng Feng & Kenji Watanabe & Takashi Taniguchi & Ning Wang & Ming-Hao Liu & Dong-Keun Ki, 2023. "Ballistic transport spectroscopy of spin-orbit-coupled bands in monolayer graphene on WSe2," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    3. Hideki Matsuoka & Tetsuro Habe & Yoshihiro Iwasa & Mikito Koshino & Masaki Nakano, 2022. "Spontaneous spin-valley polarization in NbSe2 at a van der Waals interface," Nature Communications, Nature, vol. 13(1), pages 1-7, December.
    4. Prasanna Rout & Nikos Papadopoulos & Fernando Peñaranda & Kenji Watanabe & Takashi Taniguchi & Elsa Prada & Pablo San-Jose & Srijit Goswami, 2024. "Supercurrent mediated by helical edge modes in bilayer graphene," Nature Communications, Nature, vol. 15(1), pages 1-7, December.
    5. Lukas Powalla & Jonas Kiemle & Elio J. König & Andreas P. Schnyder & Johannes Knolle & Klaus Kern & Alexander Holleitner & Christoph Kastl & Marko Burghard, 2022. "Berry curvature-induced local spin polarisation in gated graphene/WTe2 heterostructures," Nature Communications, Nature, vol. 13(1), pages 1-8, December.

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