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Interaction-driven band flattening and correlated phases in twisted bilayer graphene

Choi, Youngjoon and Kim, Hyunjin and Lewandowski, Cyprian and Peng, Yang and Thomson, Alex and Polski, Robert and Zhang, Yiran and Watanabe, Kenji and Taniguchi, Takashi and Alicea, Jason and Nadj-Perge, Stevan (2021) Interaction-driven band flattening and correlated phases in twisted bilayer graphene. Nature Physics, 17 (12). pp. 1375-1381. ISSN 1745-2473. doi:10.1038/s41567-021-01359-0.

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Flat electronic bands, characteristic of ‘magic-angle’ twisted bilayer graphene, host many correlated phenomena. Nevertheless, many properties of these bands and emerging symmetry-broken phases are still poorly understood. Here we use scanning tunnelling spectroscopy to examine the evolution of the twisted bilayer graphene bands and related gapped phases as the twist angle between the two graphene layers changes. We detect filling-dependent flattening of the bands that is appreciable even when the angle is well above the magic angle value and so the material is nominally in a weakly correlated regime. Upon approaching the magic angle, we further show that the most prominent correlated gaps begin to emerge when band flattening is maximized around certain integer fillings of electrons per moiré unit cell. Our observations are consistent with a model that suggests that a significant enhancement of the density of states caused by the band flattening triggers a cascade of symmetry-breaking transitions. Finally, we explore the temperature dependence of the cascade and identify gapped features that develop in a broad range of band fillings where superconductivity is expected. Our results highlight the role of interaction-driven band flattening in defining the electronic properties of twisted bilayer graphene.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access Paper
Kim, Hyunjin0000-0001-9886-0487
Lewandowski, Cyprian0000-0002-6944-9805
Peng, Yang0000-0002-8868-2928
Thomson, Alex0000-0002-9938-5048
Polski, Robert0000-0003-0887-8099
Zhang, Yiran0000-0002-8477-0074
Watanabe, Kenji0000-0003-3701-8119
Taniguchi, Takashi0000-0002-1467-3105
Alicea, Jason0000-0001-9979-3423
Nadj-Perge, Stevan0000-0002-2916-360X
Additional Information:© 2021 Nature Publishing Group. Received 03 February 2021; Accepted 16 August 2021; Published 04 November 2021. The authors acknowledge discussions with F. Guinea, F. von Oppen, and G. Refael. Funding: This work has been primarily supported by NSF grants DMR-2005129 and DMR-172336; and Army Research Office under Grant Award W911NF17-1-0323. Part of the STM characterization has been supported by NSF CAREER programme (DMR-1753306). Nanofabrication efforts have been in part supported by DOE-QIS programme (DE-SC0019166). S.N.-P. acknowledges support from the Sloan Foundation. J.A. and S.N.-P. also acknowledge support of the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant GBMF1250; C.L. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS Initiative (grant GBMF8682). A.T. and J.A. are grateful for the support of the Walter Burke Institute for Theoretical Physics at Caltech. Y.P. acknowledges support from the startup fund from California State University, Northridge. Y.C. and H.K. acknowledge support from the Kwanjeong Fellowship. Data availability: The data reported in Figs. 1–4 can be found on zenodo: Other data that support the findings of this study are available from the corresponding authors on reasonable request. Code availability: The code that supports the findings of this study is available from the corresponding authors on reasonable request. These authors contributed equally to this work: Youngjoon Choi, Hyunjin Kim. Author Contributions: Y.C. and H.K. fabricated samples with the help of R.P. and Y.Z., and performed STM measurements. Y.C., H.K. and S.N.-P. analysed the data. C.L. and Y.P. implemented TBG models. C.L., Y.P. and A.T. provided theoretical analysis of the model results supervised by J.A. S.N.-P. supervised the project. Y.C., H.K., C.L., Y.P., A.T., J.A. and S.N.-P. wrote the manuscript with input from other authors. The authors declare no competing interests. Peer review information: Nature Physics thanks the anonymous reviewers for their contribution to the peer review of this work.
Group:Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Army Research Office (ARO)W911NF17-1-0323
Department of Energy (DOE)DE-SC0019166
Alfred P. Sloan FoundationUNSPECIFIED
Institute for Quantum Information and Matter (IQIM)UNSPECIFIED
Gordon and Betty Moore FoundationGBMF1250
Gordon and Betty Moore FoundationGBMF8682
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
California State University, NorthridgeUNSPECIFIED
Kwanjeong Graduate FellowshipUNSPECIFIED
Subject Keywords:Electronic properties and materials; Phase transitions and critical phenomena
Issue or Number:12
Record Number:CaltechAUTHORS:20210302-094400352
Persistent URL:
Official Citation:Choi, Y., Kim, H., Lewandowski, C. et al. Interaction-driven band flattening and correlated phases in twisted bilayer graphene. Nat. Phys. 17, 1375–1381 (2021).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108266
Deposited By: Tony Diaz
Deposited On:02 Mar 2021 18:25
Last Modified:14 Dec 2021 22:57

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