Spectroscopy of a tunable moiré system with a correlated and topological flat band

Xiaomeng Liu, Cheng-Li Chiu, Jong Yeon Lee, Gelareh Farahi, Kenji Watanabe, Takashi Taniguchi, Ashvin Vishwanath and Ali Yazdani ()
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Xiaomeng Liu: Princeton University
Cheng-Li Chiu: Princeton University
Jong Yeon Lee: Harvard University
Gelareh Farahi: Princeton University
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Ashvin Vishwanath: Harvard University
Ali Yazdani: Princeton University

Nature Communications, 2021, vol. 12, issue 1, 1-7

Abstract: Abstract Moiré superlattices created by the twisted stacking of two-dimensional crystals can host electronic bands with flat energy dispersion in which enhanced interactions promote correlated electron states. The twisted double bilayer graphene (TDBG), where two Bernal bilayer graphene are stacked with a twist angle, is such a moiré system with tunable flat bands. Here, we use gate-tuned scanning tunneling spectroscopy to directly demonstrate the tunability of the band structure of TDBG with an electric field and to show spectroscopic signatures of electronic correlations and topology for its flat band. Our spectroscopic experiments are in agreement with a continuum model of TDBG band structure and reveal signatures of a correlated insulator gap at partial filling of its isolated flat band. The topological properties of this flat band are probed with the application of a magnetic field, which leads to valley polarization and the splitting of Chern bands with a large effective g-factor.

Date: 2021
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DOI: 10.1038/s41467-021-23031-0

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