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

Abstract

Spin-orbit coupling (SOC) is the key to realizing time-reversal-invariant topological phases of matter. SOC was predicted by Kane and Mele to stabilize a quantum spin Hall insulator; however, the weak intrinsic SOC in monolayer graphene has precluded experimental observation in this material. In this work, we exploit a layer-selective proximity effect-achieved via a van der Waals contact with a semiconducting transition-metal dichalcogenide 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 close. Our electrical transport measurements reveal that the inverted phase has a conductivity of approximately e 2/ 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 anomalousmore » 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.« less

Authors:
 [1];  [1];  [2];  [2];  [1];  [1];  [3];  [3];  [4];  [4];  [2];  [5];  [1]
  1. Univ. of California, Santa Barbara, CA (United States). Dept. of Physics
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Physics
  3. Columbia Univ., New York, NY (United States). Dept. of Mechanical Engineering
  4. National Inst. for Materials Science, Tsukuba, Ibaraki (Japan)
  5. Univ. of California, Berkeley, CA (United States). Dept. of Physics
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1572030
Grant/Contract Number:  
AC02-05CH11231; SC0016703
Resource Type:
Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 571; Journal Issue: 7763; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Island, J. O., Cui, X., Lewandowski, C., Khoo, J. Y., Spanton, E. M., Zhou, H., Rhodes, D., Hone, J. C., Taniguchi, T., Watanabe, K., Levitov, L. S., Zaletel, M. P., and Young, A. F. Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect. United States: N. p., 2019. Web. doi:10.1038/s41586-019-1304-2.
Island, J. O., Cui, X., Lewandowski, C., Khoo, J. Y., Spanton, E. M., Zhou, H., Rhodes, D., Hone, J. C., Taniguchi, T., Watanabe, K., Levitov, L. S., Zaletel, M. P., & Young, A. F. Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect. United States. doi:10.1038/s41586-019-1304-2.
Island, J. O., Cui, X., Lewandowski, C., Khoo, J. Y., Spanton, E. M., Zhou, H., Rhodes, D., Hone, J. C., Taniguchi, T., Watanabe, K., Levitov, L. S., Zaletel, M. P., and Young, A. F. Wed . "Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect". United States. doi:10.1038/s41586-019-1304-2.
@article{osti_1572030,
title = {Spin–orbit-driven band inversion in bilayer graphene by the van der Waals proximity effect},
author = {Island, J. O. and Cui, X. and Lewandowski, C. and Khoo, J. Y. and Spanton, E. M. and Zhou, H. and Rhodes, D. and Hone, J. C. and Taniguchi, T. and Watanabe, K. and Levitov, L. S. and Zaletel, M. P. and Young, A. F.},
abstractNote = {Spin-orbit coupling (SOC) is the key to realizing time-reversal-invariant topological phases of matter. SOC was predicted by Kane and Mele to stabilize a quantum spin Hall insulator; however, the weak intrinsic SOC in monolayer graphene has precluded experimental observation in this material. In this work, we exploit a layer-selective proximity effect-achieved via a van der Waals contact with a semiconducting transition-metal dichalcogenide 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 close. 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.},
doi = {10.1038/s41586-019-1304-2},
journal = {Nature (London)},
number = 7763,
volume = 571,
place = {United States},
year = {2019},
month = {6}
}

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    Works referencing / citing this record:

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    journal, November 2017


    Tunable interacting composite fermion phases in a half-filled bilayer-graphene Landau level
    journal, September 2017


    Electrical gate control of spin current in van der Waals heterostructures at room temperature
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    • Dankert, André; Dash, Saroj P.
    • Nature Communications, Vol. 8, Issue 1
    • DOI: 10.1038/ncomms16093

    Spin–orbit proximity effect in graphene
    journal, September 2014

    • Avsar, A.; Tan, J. Y.; Taychatanapat, T.
    • Nature Communications, Vol. 5, Issue 1
    • DOI: 10.1038/ncomms5875

    Strong interface-induced spin–orbit interaction in graphene on WS2
    journal, September 2015

    • Wang, Zhe; Ki, Dong–Keun; Chen, Hua
    • Nature Communications, Vol. 6, Issue 1
    • DOI: 10.1038/ncomms9339

    Boron nitride substrates for high-quality graphene electronics
    journal, August 2010

    • Dean, C. R.; Young, A. F.; Meric, I.
    • Nature Nanotechnology, Vol. 5, Issue 10, p. 722-726
    • DOI: 10.1038/nnano.2010.172

    Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene
    journal, October 2017


    Ambipolar Landau levels and strong band-selective carrier interactions in monolayer WSe2
    journal, March 2018

    • Gustafsson, Martin V.; Yankowitz, Matthew; Forsythe, Carlos
    • Nature Materials, Vol. 17, Issue 5
    • DOI: 10.1038/s41563-018-0036-2

    Strongly anisotropic spin relaxation in graphene–transition metal dichalcogenide heterostructures at room temperature
    journal, December 2017

    • Benítez, L. Antonio; Sierra, Juan F.; Savero Torres, Williams
    • Nature Physics, Vol. 14, Issue 3
    • DOI: 10.1038/s41567-017-0019-2

    Tunable spin–orbit coupling and symmetry-protected edge states in graphene/WS 2
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    One-Dimensional Electrical Contact to a Two-Dimensional Material
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    Strange topological materials are popping up everywhere physicists look
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