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Cascade of electronic transitions in magic-angle twisted bilayer graphene

Author

Listed:
  • Dillon Wong

    (Princeton University
    Princeton University)

  • Kevin P. Nuckolls

    (Princeton University
    Princeton University)

  • Myungchul Oh

    (Princeton University
    Princeton University)

  • Biao Lian

    (Princeton University)

  • Yonglong Xie

    (Princeton University
    Princeton University
    Harvard University
    Massachusetts Institute of Technology)

  • Sangjun Jeon

    (Princeton University
    Princeton University
    Chung-Ang University)

  • Kenji Watanabe

    (National Institute for Material Science)

  • Takashi Taniguchi

    (National Institute for Material Science)

  • B. Andrei Bernevig

    (Princeton University)

  • Ali Yazdani

    (Princeton University
    Princeton University)

Abstract

Magic-angle twisted bilayer graphene exhibits a variety of electronic states, including correlated insulators1–3, superconductors2–4 and topological phases3,5,6. Understanding the microscopic mechanisms responsible for these phases requires determination of the interplay between electron–electron interactions and quantum degeneracy (the latter is due to spin and valley degrees of freedom). Signatures of strong electron–electron correlations have been observed at partial fillings of the flat electronic bands in recent spectroscopic measurements7–10, and transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moiré unit cell2–4. However, the interplay between interaction effects and the degeneracy of the system is currently unclear. Here we report a cascade of transitions in the spectroscopic properties of magic-angle twisted bilayer graphene as a function of electron filling, determined using high-resolution scanning tunnelling microscopy. We find distinct changes in the chemical potential and a rearrangement of the low-energy excitations at each integer filling of the moiré flat bands. These spectroscopic features are a direct consequence of Coulomb interactions, which split the degenerate flat bands into Hubbard sub-bands. We find these interactions, the strength of which we can extract experimentally, to be surprisingly sensitive to the presence of a perpendicular magnetic field, which strongly modifies the spectroscopic transitions. The cascade of transitions that we report here characterizes the correlated high-temperature parent phase11,12 from which various insulating and superconducting ground-state phases emerge at low temperatures in magic-angle twisted bilayer graphene.

Suggested Citation

  • Dillon Wong & Kevin P. Nuckolls & Myungchul Oh & Biao Lian & Yonglong Xie & Sangjun Jeon & Kenji Watanabe & Takashi Taniguchi & B. Andrei Bernevig & Ali Yazdani, 2020. "Cascade of electronic transitions in magic-angle twisted bilayer graphene," Nature, Nature, vol. 582(7811), pages 198-202, June.
  • Handle: RePEc:nat:nature:v:582:y:2020:i:7811:d:10.1038_s41586-020-2339-0
    DOI: 10.1038/s41586-020-2339-0
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    Citations

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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. J. Díez-Mérida & A. Díez-Carlón & S. Y. Yang & Y.-M. Xie & X.-J. Gao & J. Senior & K. Watanabe & T. Taniguchi & X. Lu & A. P. Higginbotham & K. T. Law & Dmitri K. Efetov, 2023. "Symmetry-broken Josephson junctions and superconducting diodes in magic-angle twisted bilayer graphene," Nature Communications, Nature, vol. 14(1), pages 1-7, December.
    3. Le Liu & Shihao Zhang & Yanbang Chu & Cheng Shen & Yuan Huang & Yalong Yuan & Jinpeng Tian & Jian Tang & Yiru Ji & Rong Yang & Kenji Watanabe & Takashi Taniguchi & Dongxia Shi & Jianpeng Liu & Wei Yan, 2022. "Isospin competitions and valley polarized correlated insulators in twisted double bilayer graphene," Nature Communications, Nature, vol. 13(1), pages 1-7, December.
    4. Alberto Montanaro & Giulia Piccinini & Vaidotas Mišeikis & Vito Sorianello & Marco A. Giambra & Stefano Soresi & Luca Giorgi & Antonio D’Errico & K. Watanabe & T. Taniguchi & Sergio Pezzini & Camilla , 2023. "Sub-THz wireless transmission based on graphene-integrated optoelectronic mixer," Nature Communications, Nature, vol. 14(1), pages 1-14, December.
    5. 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.
    6. Keshav Singh & Aaron Chew & Jonah Herzog-Arbeitman & B. Andrei Bernevig & Oskar Vafek, 2024. "Topological heavy fermions in magnetic field," Nature Communications, Nature, vol. 15(1), pages 1-12, December.
    7. Si-yu Li & Zhengwen Wang & Yucheng Xue & Yingbo Wang & Shihao Zhang & Jianpeng Liu & Zheng Zhu & Kenji Watanabe & Takashi Taniguchi & Hong-jun Gao & Yuhang Jiang & Jinhai Mao, 2022. "Imaging topological and correlated insulating states in twisted monolayer-bilayer graphene," Nature Communications, Nature, vol. 13(1), pages 1-7, December.

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