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Multiple flat bands and topological Hofstadter butterfly in twisted bilayer graphene close to the second magic angle

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Lu Xiaobo, Lian Biao, Chaudhary Gaurav, Piot Benjamin A., Romagnoli Giulio, Watanabe Kenji, Taniguchi Takashi, Poggio Martino, MacDonald Allan H., Bernevig B. Andrei, Efetov Dmitri K.,
Project Discovery and Nanoengineering of Novel Skyrmion-hosting Materials
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Original article (peer-reviewed)

Journal Proceedings of the National Academy of Sciences
Volume (Issue) 118(30)
Page(s) e210000611 - e210000611
Title of proceedings Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.2100006118

Open Access

URL https://arxiv.org/abs/2006.13963
Type of Open Access Repository (Green Open Access)

Abstract

Moiré superlattices in two-dimensional van der Waals heterostructures provide an efficient way to engineer electron band properties. The recent discovery of exotic quantum phases and their interplay in twisted bilayer graphene (tBLG) has made this moiré system one of the most renowned condensed matter platforms. So far studies of tBLG have been mostly focused on the lowest two flat moiré bands at the first magic angle θ m1 ∼ 1.1°, leaving high-order moiré bands and magic angles largely unexplored. Here we report an observation of multiple well-isolated flat moiré bands in tBLG close to the second magic angle θ m2 ∼ 0.5°, which cannot be explained without considering electron–election interactions. With high magnetic field magnetotransport measurements we further reveal an energetically unbound Hofstadter butterfly spectrum in which continuously extended quantized Landau level gaps cross all trivial band gaps. The connected Hofstadter butterfly strongly evidences the topologically nontrivial textures of the multiple moiré bands. Overall, our work provides a perspective for understanding the quantum phases in tBLG and the fractal Hofstadter spectra of multiple topological bands.
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