Fractional Chern insulators in magic-angle twisted bilayer graphene

Journal Article · Wed Dec 15 00:00:00 EST 2021 · Nature (London)

DOI:https://doi.org/10.1038/s41586-021-04002-3· OSTI ID:1904548

Xie, Yonglong ^[1]; Pierce, Andrew T. ^[2]; Park, Jeong Min ^[3]; Parker, Daniel E. ^[2]; Khalaf, Eslam ^[2]; Ledwith, Patrick ^[2]; Cao, Yuan ^[3]; Lee, Seung Hwan ^[2]; Chen, Shaowen ^[2]; Forrester, Patrick R. ^[2]; Watanabe, Kenji ^[4]; Taniguchi, Takashi ^[4]; Vishwanath, Ashvin ^[2]; Jarillo-Herrero, Pablo ^[3]; Yacoby, Amir ^[2]

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1. Harvard Univ., Cambridge, MA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Harvard Univ., Cambridge, MA
2. Harvard Univ., Cambridge, MA (United States)
3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
4. National Institute for Materials Science (NIMS), Tsukuba (Japan)

Fractional Chern insulators (FCIs) are lattice analogues of fractional quantum Hall states that may provide a new avenue towards manipulating non-Abelian excitations. Early theoretical studies have predicted their existence in systems with flat Chern bands and highlighted the critical role of a particular quantum geometry. However, FCI states have been observed only in Bernal-stacked bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN), in which a very large magnetic field is responsible for the existence of the Chern bands, precluding the realization of FCIs at zero field. By contrast, magic-angle twisted BLG supports flat Chern bands at zero magnetic field and therefore offers a promising route towards stabilizing zero-field FCIs. Here we report the observation of eight FCI states at low magnetic field in magic-angle twisted BLG enabled by high-resolution local compressibility measurements. The first of these states emerge at 5 T, and their appearance is accompanied by the simultaneous disappearance of nearby topologically trivial charge density wave states. We demonstrate that, unlike the case of the BLG/hBN platform, the principal role of the weak magnetic field is merely to redistribute the Berry curvature of the native Chern bands and thereby realize a quantum geometry favourable for the emergence of FCIs. Our findings strongly suggest that FCIs may be realized at zero magnetic field and pave the way for the exploration and manipulation of anyonic excitations in flat moiré Chern bands.

• Research Organization: Harvard Univ., Cambridge, MA (United States)
• Sponsoring Organization: German National Academy of Sciences; Gordon and Betty Moore Foundation (GBMF); Japan Society for the Promotion of Science (JSPS) (KAKENHI); Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT); National Science Foundation (NSF); Simons Foundation; US Army Research Office (ARO); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
• Grant/Contract Number: SC0001819; SC0019300
• OSTI ID: 1904548
• Journal Information: Nature (London), Journal Name: Nature (London) Journal Issue: 7889 Vol. 600; ISSN 0028-0836
• Publisher: Nature Publishing Group
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
electronic properties and materials
topological matter