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Moiré superlattices engineer band properties and enable observation of fractal energy spectra of Hofstadter butterfly. Specifically, small-angle moiré results in flat bands due to strong hybridization between layers. To date, the major focus has been to gain new insights into correlated-electron physics hosted by the flat bands. However, the implications of the topology of these moiré bands within the framework of single-particle physics are little explored experimentally. An outstanding problem is to understand the effect of band topology on Hofstadter physics, which does not require electron correlations. In this work, we use a tunable topological band platform, namely twisted double bilayer graphene (TDBG), to experimentally study Chern state switching in the Hofstadter regime. In TDBG, unlike in TBG, the perpendicular electric field can tune the band structure as well as its topological properties like valley Chern numbers. We show that the nontrivial topology reflects in the Hofstadter spectra, in particular, displaying a cascade of Hofstadter gaps that switch their Chern numbers one-at-a-time as we vary the electric field. Our experiments together with theoretical calculations suggest a crucial role of charge polarization in this system that changes concomitantly with topological transitions. The layer polarization is likely to play an important role in the topological states in few-layer twisted systems. Moreover, our work establishes TDBG as a novel Hofstadter platform with nontrivial magnetoelectric coupling.

権利情報:

• Creative Commons BY Attribution 4.0 International
  

キーワード: Moiré superlattices, Hofstadter butterfly, Chern state

刊行年月日: 2022-12-16

出版者: Springer Science and Business Media LLC

掲載誌:

• Nature Communications (ISSN: 20411723) vol. 13 issue. 1 7781

研究助成金:

原稿種別: 出版者版 (Version of record)

MDR DOI:

公開URL: https://doi.org/10.1038/s41467-022-35421-z

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更新時刻: 2025-02-27 12:30:39 +0900

MDRでの公開時刻: 2025-02-27 12:30:39 +0900