Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

Minhao He, Ya-Hui Zhang, Yuhao Li, Zaiyao Fei, Kenji Watanabe, Takashi Taniguchi, Xiaodong Xu () and Matthew Yankowitz ()
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Minhao He: University of Washington
Ya-Hui Zhang: Harvard University
Yuhao Li: University of Washington
Zaiyao Fei: University of Washington
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Xiaodong Xu: University of Washington
Matthew Yankowitz: University of Washington

Nature Communications, 2021, vol. 12, issue 1, 1-8

Abstract: Abstract Flat band moiré superlattices have recently emerged as unique platforms for investigating the interplay between strong electronic correlations, nontrivial band topology, and multiple isospin ‘flavor’ symmetries. Twisted monolayer-bilayer graphene (tMBG) is an especially rich system owing to its low crystal symmetry and the tunability of its bandwidth and topology with an external electric field. Here, we find that orbital magnetism is abundant within the correlated phase diagram of tMBG, giving rise to the anomalous Hall effect in correlated metallic states nearby most odd integer fillings of the flat conduction band, as well as correlated Chern insulator states stabilized in an external magnetic field. The behavior of the states at zero field appears to be inconsistent with simple spin and valley polarization for the specific range of twist angles we investigate, and instead may plausibly result from an intervalley coherent (IVC) state with an order parameter that breaks time reversal symmetry. The application of a magnetic field further tunes the competition between correlated states, in some cases driving first-order topological phase transitions. Our results underscore the rich interplay between closely competing correlated ground states in tMBG, with possible implications for probing exotic IVC ordering.

Date: 2021
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DOI: 10.1038/s41467-021-25044-1

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