TY - JOUR
T1 - Cascade of electronic transitions in magic-angle twisted bilayer graphene
AU - Wong, Dillon
AU - Nuckolls, Kevin P.
AU - Oh, Myungchul
AU - Lian, Biao
AU - Xie, Yonglong
AU - Jeon, Sangjun
AU - Watanabe, Kenji
AU - Taniguchi, Takashi
AU - Bernevig, B. Andrei
AU - Yazdani, Ali
N1 - Funding Information:
Acknowledgements We thank P. Jarillo-Herrero, E. Berg, A. Stern, A. H. MacDonald, B. Jäck, X. Liu, C.-L. Chiu, N. P. Ong, S. Wu, S. Todadri and S. Kahn for useful discussions. This work was primarily supported by the Gordon and Betty Moore Foundation as part of the EPiQS initiative (grant GBMF4530) and by DOE-BES grant DE-FG02-07ER46419. Other support for the experimental work was provided by NSF-MRSEC through the Princeton Center for Complex Materials grants DMR-1420541, NSF-DMR-1608848 and NSF-DMR-1904442, by ExxonMobil through the Andlinger Center for Energy and the Environment at Princeton, and by the Princeton Catalysis Initiative. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, from A3 Foresight by JSPS and from CREST (grant JPMJCR15F3), JST. B.L. acknowledges support from the Princeton Center for Theoretical Science at Princeton University. B.A.B. acknowledges support from Department of Energy grant DE-SC0016239, a Simons Investigator Award, the Packard Foundation, the Schmidt Fund for Innovative Research, NSF EAGER grant DMR-1643312, and NSF-MRSEC DMR-1420541. A.Y. acknowledges the hospitality of Trinity College and the Cavendish Laboratory in Cambridge, UK, during the preparation of this manuscript, which was also funded in part by a QuantEmX grant from the Institute for Complex Adaptive Matter and the Gordon and Betty Moore Foundation (grant GBMF5305).
Publisher Copyright:
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2020/6/11
Y1 - 2020/6/11
N2 - Magic-angle twisted bilayer graphene exhibits a variety of electronic states, including correlated insulators1–3, superconductors2–4 and topological phases3,5,6. 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 measurements7–10, and transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moiré unit cell2–4. 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 moiré 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 phase11,12 from which various insulating and superconducting ground-state phases emerge at low temperatures in magic-angle twisted bilayer graphene.
AB - Magic-angle twisted bilayer graphene exhibits a variety of electronic states, including correlated insulators1–3, superconductors2–4 and topological phases3,5,6. 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 measurements7–10, and transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moiré unit cell2–4. 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 moiré 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 phase11,12 from which various insulating and superconducting ground-state phases emerge at low temperatures in magic-angle twisted bilayer graphene.
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U2 - 10.1038/s41586-020-2339-0
DO - 10.1038/s41586-020-2339-0
M3 - Article
C2 - 32528095
AN - SCOPUS:85086356485
SN - 0028-0836
VL - 582
SP - 198
EP - 202
JO - Nature
JF - Nature
IS - 7811
ER -