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Strong electron correlation and nontrivial band topology are two crucial strategies on exploring the novel quantum phases in condensed matter physics study1-5. When strong Coulomb correlations meets band topology together, exotic quantum phenomena are expected6,7. As one succeed example, the flat Chern bands with valley spin degeneracy can be globally split by strong Coulomb interactions, leading to various symmetry breaking states with topological nontrivial properties in twisted graphene systems8-10. Here, through a comprehensive spectrum study, for the first time we report an effective locking between strong local correlation effects and the intrinsic Chern bands in twisted mono-bilayer graphene near the magic angle. An intense competition between the local correlation physics that tries to halt the electrons motion and non-zero Chern number that obscures the electron localization generates intriguing electron freezing and Chern number fragmentation in real space. The strong Coulomb correlations give rise to an unusual charge localization within the moiré supercell, leading to a gate tunable electron crystal. It provides a new local mechanism on realizing the correlated insulating state at integer filling in moiré graphene systems. Moreover, the nontrivial band topology is encoded into the electron crystal, which would result in a topological mosaic, and is evidenced by an emergent topological order through direct spectrum images. It acts as a topological marker to visualize the Chern band in real space down to nanoscale without any request of external magnetic field. Our result illustrates an efficient strategy for entwining and engineering topological physics with a strong electron correlation.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Flat bands, twisted monolayer-bilayer graphene, electron crystal phase

Date published: 2022-07-22

Publisher: Springer Science and Business Media LLC

Journal:

• Nature Communications (ISSN: 20411723) vol. 13 issue. 1 4225

Funding:

• National Natural Science Foundation of China 11974347
• National Natural Science Foundation of China 12074377

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41467-022-31851-x

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Updated at: 2025-02-27 16:30:20 +0900

Published on MDR: 2025-02-27 16:30:20 +0900