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Evidence for unconventional superconductivity in twisted trilayer graphene

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  • Hyunjin Kim

    (California Institute of Technology
    Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology)

  • Youngjoon Choi

    (California Institute of Technology
    Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology)

  • Cyprian Lewandowski

    (Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology
    Walter Burke Institute for Theoretical Physics, California Institute of Technology)

  • Alex Thomson

    (Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology
    Walter Burke Institute for Theoretical Physics, California Institute of Technology
    University of California, Davis)

  • Yiran Zhang

    (California Institute of Technology
    Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology)

  • Robert Polski

    (California Institute of Technology
    Institute for Quantum Information and Matter, California Institute of Technology)

  • Kenji Watanabe

    (National Institute for Materials Science)

  • Takashi Taniguchi

    (National Institute for Materials Science)

  • Jason Alicea

    (Institute for Quantum Information and Matter, California Institute of Technology
    California Institute of Technology
    Walter Burke Institute for Theoretical Physics, California Institute of Technology)

  • Stevan Nadj-Perge

    (California Institute of Technology
    Institute for Quantum Information and Matter, California Institute of Technology)

Abstract

Magic-angle twisted trilayer graphene (MATTG) has emerged as a moiré material that exhibits strong electronic correlations and unconventional superconductivity1,2. However, local spectroscopic studies of this system are still lacking. Here we perform high-resolution scanning tunnelling microscopy and spectroscopy of MATTG that reveal extensive regions of atomic reconstruction favouring mirror-symmetric stacking. In these regions, we observe symmetry-breaking electronic transitions and doping-dependent band-structure deformations similar to those in magic-angle bilayers, as expected theoretically given the commonality of flat bands3,4. Most notably in a density window spanning two to three holes per moiré unit cell, the spectroscopic signatures of superconductivity are manifest as pronounced dips in the tunnelling conductance at the Fermi level accompanied by coherence peaks that become gradually suppressed at elevated temperatures and magnetic fields. The observed evolution of the conductance with doping is consistent with a gate-tunable transition from a gapped superconductor to a nodal superconductor, which is theoretically compatible with a sharp transition from a Bardeen–Cooper–Schrieffer superconductor to a Bose–Einstein-condensation superconductor with a nodal order parameter. Within this doping window, we also detect peak–dip–hump structures that suggest that superconductivity is driven by strong coupling to bosonic modes of MATTG. Our results will enable further understanding of superconductivity and correlated states in graphene-based moiré structures beyond twisted bilayers5.

Suggested Citation

  • Hyunjin Kim & Youngjoon Choi & Cyprian Lewandowski & Alex Thomson & Yiran Zhang & Robert Polski & Kenji Watanabe & Takashi Taniguchi & Jason Alicea & Stevan Nadj-Perge, 2022. "Evidence for unconventional superconductivity in twisted trilayer graphene," Nature, Nature, vol. 606(7914), pages 494-500, June.
  • Handle: RePEc:nat:nature:v:606:y:2022:i:7914:d:10.1038_s41586-022-04715-z
    DOI: 10.1038/s41586-022-04715-z
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    Cited by:

    1. Anushree Datta & M. J. Calderón & A. Camjayi & E. Bascones, 2023. "Heavy quasiparticles and cascades without symmetry breaking in twisted bilayer graphene," Nature Communications, Nature, vol. 14(1), pages 1-8, December.
    2. Maine Christos & Subir Sachdev & Mathias S. Scheurer, 2023. "Nodal band-off-diagonal superconductivity in twisted graphene superlattices," Nature Communications, Nature, vol. 14(1), pages 1-11, December.
    3. Richen Xiong & Samuel L. Brantly & Kaixiang Su & Jacob H. Nie & Zihan Zhang & Rounak Banerjee & Hayley Ruddick & Kenji Watanabe & Takashi Taniguchi & Seth Ariel Tongay & Cenke Xu & Chenhao Jin, 2024. "Tunable exciton valley-pseudospin orders in moiré superlattices," Nature Communications, Nature, vol. 15(1), pages 1-10, December.
    4. Bin Hu & Hui Chen & Yuhan Ye & Zihao Huang & Xianghe Han & Zhen Zhao & Hongqin Xiao & Xiao Lin & Haitao Yang & Ziqiang Wang & Hong-Jun Gao, 2024. "Evidence of a distinct collective mode in Kagome superconductors," Nature Communications, Nature, vol. 15(1), pages 1-11, December.

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