期刊
NATURE
卷 582, 期 7811, 页码 198-+出版社
NATURE RESEARCH
DOI: 10.1038/s41586-020-2339-0
关键词
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资金
- Gordon and Betty Moore Foundation as part of the EPiQS initiative [GBMF4530]
- DOE-BES [DE-FG02-07ER46419]
- NSF-MRSEC through the Princeton Center for Complex Materials [DMR-1420541, NSF-DMR-1608848, NSF-DMR-1904442]
- ExxonMobil through the Andlinger Center for Energy and the Environment at Princeton
- Princeton Catalysis Initiative
- Elemental Strategy Initiative by the MEXT, Japan
- A3 Foresight by JSPS
- CREST, JST [JPMJCR15F3]
- Princeton Center for Theoretical Science at Princeton University
- Department of Energy [DE-SC0016239]
- Simons Investigator Award
- Packard Foundation
- Schmidt Fund for Innovative Research
- NSF EAGER [DMR-1643312]
- NSF-MRSEC [DMR-1420541]
- Institute for Complex Adaptive Matter
- Gordon and Betty Moore Foundation [GBMF5305]
Magic-angle twisted bilayer graphene exhibits a variety of electronic states, including correlated insulators(1-3), superconductors(2-4)and topological phases(3,5,6). Understanding the microscopic mechanisms responsible for these phases requires determination of the interplay between electron-electron interactions and quantum degeneracy (the latter is due to spin and valley degrees of freedom). Signatures of strong electron-electron correlations have been observed at partial fillings of the flat electronic bands in recent spectroscopic measurements(7-10), and transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moire unit cell(2-4). However, the interplay between interaction effects and the degeneracy of the system is currently unclear. Here we report a cascade of transitions in the spectroscopic properties of magic-angle twisted bilayer graphene as a function of electron filling, determined using high-resolution scanning tunnelling microscopy. We find distinct changes in the chemical potential and a rearrangement of the low-energy excitations at each integer filling of the moire flat bands. These spectroscopic features are a direct consequence of Coulomb interactions, which split the degenerate flat bands into Hubbard sub-bands. We find these interactions, the strength of which we can extract experimentally, to be surprisingly sensitive to the presence of a perpendicular magnetic field, which strongly modifies the spectroscopic transitions. The cascade of transitions that we report here characterizes the correlated high-temperature parent phase(11,12)from which various insulating and superconducting ground-state phases emerge at low temperatures in magic-angle twisted bilayer graphene. Electron-electron interactions in magic-angle twisted bilayer graphene can split usually degenerate electronic bands, giving rise to a cascade of electronic transitions revealed by spectroscopy.
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