TY - JOUR
T1 - Symmetry-broken Chern insulators and Rashba-like Landau-level crossings in magic-angle bilayer graphene
AU - Das, Ipsita
AU - Lu, Xiaobo
AU - Herzog-Arbeitman, Jonah
AU - Song, Zhi Da
AU - Watanabe, Kenji
AU - Taniguchi, Takashi
AU - Bernevig, B. Andrei
AU - Efetov, Dmitri K.
N1 - Funding Information:
We are grateful for fruitful discussions with A. Yazdani, E. Andrei, D. Abanin and A. Young. Funding: D.K.E. acknowledges support from the Ministry of Economy and Competitiveness of Spain through the ‘Severo Ochoa’ programme for Centres of Excellence in R&D (SE5-0522), Fundació Privada Cellex, Fundació Privada Mir-Puig, the Generalitat de Catalunya through the CERCA programme, funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 852927) and the La Caixa Foundation. B.A.B. was supported by the Department of Energy grant no. DE-SC0016239, the Schmidt Fund for Innovative Research, Simons Investigator grant no. 404513 and the Packard Foundation. Further support was provided by the National Science Foundation EAGER grant no. DMR 1643312, NSF-MRSEC DMR-1420541, US–Israel BSF grant no. 2018226, ONR no. N00014-20-1-2303 and Princeton Global Network Funds. I.D. acknowledges support from the INphINIT ‘la Caixa’ (ID 100010434) fellowship programme (LCF/BQ/DI19/11730030).
Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2021/6
Y1 - 2021/6
N2 - Flat bands in magic-angle twisted bilayer graphene (MATBG) have recently emerged as a rich platform to explore strong correlations1, superconductivity2–5 and magnetism3,6,7. However, the phases of MATBG in a magnetic field and what they reveal about the zero-field phase diagram remain relatively uncharted. Here we report a rich sequence of wedge-like regions of quantized Hall conductance with Chern numbers C = ±1, ±2, ±3 and ±4, which nucleate from integer fillings of the moiré unit cell v = ±3, ±2, ±1 and 0, respectively. We interpret these phases as spin- and valley-polarized many-body Chern insulators. The exact sequence and correspondence of the Chern numbers and filling factors suggest that these states are directly driven by electronic interactions, which specifically break the time-reversal symmetry in the system. We further study the yet unexplored higher-energy dispersive bands with a Rashba-like dispersion. The analysis of Landau-level crossings enables a parameter-free comparison to a newly derived ‘magic series’ of level crossings in a magnetic field and provides constraints on the parameters of the Bistritzer–MacDonald MATBG Hamiltonian. Overall, our data provide direct insights into the complex nature of symmetry breaking in MATBG and allow for the quantitative tests of the proposed microscopic scenarios for its electronic phases.
AB - Flat bands in magic-angle twisted bilayer graphene (MATBG) have recently emerged as a rich platform to explore strong correlations1, superconductivity2–5 and magnetism3,6,7. However, the phases of MATBG in a magnetic field and what they reveal about the zero-field phase diagram remain relatively uncharted. Here we report a rich sequence of wedge-like regions of quantized Hall conductance with Chern numbers C = ±1, ±2, ±3 and ±4, which nucleate from integer fillings of the moiré unit cell v = ±3, ±2, ±1 and 0, respectively. We interpret these phases as spin- and valley-polarized many-body Chern insulators. The exact sequence and correspondence of the Chern numbers and filling factors suggest that these states are directly driven by electronic interactions, which specifically break the time-reversal symmetry in the system. We further study the yet unexplored higher-energy dispersive bands with a Rashba-like dispersion. The analysis of Landau-level crossings enables a parameter-free comparison to a newly derived ‘magic series’ of level crossings in a magnetic field and provides constraints on the parameters of the Bistritzer–MacDonald MATBG Hamiltonian. Overall, our data provide direct insights into the complex nature of symmetry breaking in MATBG and allow for the quantitative tests of the proposed microscopic scenarios for its electronic phases.
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U2 - 10.1038/s41567-021-01186-3
DO - 10.1038/s41567-021-01186-3
M3 - Article
AN - SCOPUS:85101915191
SN - 1745-2473
VL - 17
SP - 710
EP - 714
JO - Nature Physics
JF - Nature Physics
IS - 6
ER -