Strongly correlated Chern insulators in magic-angle twisted bilayer graphene

Nuckolls, Kevin P.; Oh, Myungchul; Wong, Dillon; Lian, Biao; Watanabe, Kenji; Taniguchi, Takashi; Bernevig, B. Andrei; Yazdani, Ali

doi:10.1038/s41586-020-3028-8

Strongly correlated Chern insulators in magic-angle twisted bilayer graphene

Journal Article · Sun Dec 13 23:00:00 EST 2020 · Nature (London)

DOI:https://doi.org/10.1038/s41586-020-3028-8· OSTI ID:1780898

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Princeton Univ., NJ (United States); Princeton University
Princeton Univ., NJ (United States)
National Institute for Materials Science (NIMS), Tsukuba (Japan)

Interactions between electrons and the topology of their energy bands can create unusual quantum phases of matter. Most topological electronic phases appear in systems with weak electron–electron interactions. The instances in which topological phases emerge only as a result of strong interactions are rare and mostly limited to those realized in intense magnetic fields. The discovery of flat electronic bands with topological character in magic-angle twisted bilayer graphene (MATBG) has created a unique opportunity to search for strongly correlated topological phases. Here we introduce a local spectroscopic technique using a scanning tunnelling microscope to detect a sequence of topological insulators in MATBG with Chern numbers C = ±1, ±2 and ±3, which form near filling factors of ±3, ±2 and ±1 electrons per moiré unit cell, respectively, and are stabilized by modest magnetic fields. One of the phases detected here (C = +1) was previously observed when the sublattice symmetry of MATBG was intentionally broken by a hexagonal boron nitride substrate, with interactions having a secondary role. We also demonstrate that strong electron–electron interactions alone can produce not only the previously observed phase, but also other unexpected Chern insulating phases in MATBG. The full sequence of phases that we observe can be understood by postulating that strong correlations favour breaking time-reversal symmetry to form Chern insulators that are stabilized by weak magnetic fields. Our findings illustrate that many-body correlations can create topological phases in moiré systems beyond those anticipated from weakly interacting models.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Univ., NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES); Gordon and Betty Moore Foundation (GBMF); National Science Foundation (NSF); US Department of the Navy, Office of Naval Research (ONR)

Grant/Contract Number:: FG02-07ER46419; SC0016239

OSTI ID:: 1780898

Journal Information:: Nature (London), Journal Name: Nature (London) Journal Issue: 7839 Vol. 588; ISSN 0028-0836

Publisher:: Nature Publishing GroupCopyright Statement

Country of Publication:: United States

Language:: English

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