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Correlation-driven topological phases in magic-angle twisted bilayer graphene

Choi, Youngjoon and Kim, Hyunjin and Peng, Yang and Thomson, Alex and Lewandowski, Cyprian and Polski, Robert and Zhang, Yiran and Arora, Harpreet Singh and Watanabe, Kenji and Taniguchi, Takashi and Alicea, Jason and Nadj-Perge, Stevan (2021) Correlation-driven topological phases in magic-angle twisted bilayer graphene. Nature, 589 (7843). pp. 536-541. ISSN 0028-0836. doi:10.1038/s41586-020-03159-7.

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[img] PDF (includes the continuum and ten-band model details that are used to calculate the spectrum in Fig. 1g, Extended Data Fig. 7, Extended Data Fig. 8 and Extended Data Fig. 9) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 1: Optical image of the device and STM topography of WSe2/hBN boundary) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 2: AA site point spectra versus gate voltage with magnetic field) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 3: Evolution of cascade with magnetic field) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 4: Quantum Hall ferromagnetic states at the zLL) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 5: Chern insulating phases in the valence band) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 6: C = −1 phase in a high-resolution angle-dependent LDOS map at B = 7 T) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 7: Spectrum of a continuum model taking into account the effects of a displacement field) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 8: Estimated ratio between correlation and kinetic-energy scales, U/W, as a function of twist angle and magnetic field) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 9: Possible MATBG band-structure scenarios obtained using the ten-band model and corresponding LL spectra) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 10: Landau fan diagram overlaid on experimental data for different choices of gate voltages corresponding to ν = ±4) - Supplemental Material
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Magic-angle twisted bilayer graphene (MATBG) exhibits a range of correlated phenomena that originate from strong electron–electron interactions. These interactions make the Fermi surface highly susceptible to reconstruction when ±1, ±2 and ±3 electrons occupy each moiré unit cell, and lead to the formation of various correlated phases. Although some phases have been shown to have a non-zero Chern number, the local microscopic properties and topological character of many other phases have not yet been determined. Here we introduce a set of techniques that use scanning tunnelling microscopy to map the topological phases that emerge in MATBG in a finite magnetic field. By following the evolution of the local density of states at the Fermi level with electrostatic doping and magnetic field, we create a local Landau fan diagram that enables us to assign Chern numbers directly to all observed phases. We uncover the existence of six topological phases that arise from integer fillings in finite fields and that originate from a cascade of symmetry-breaking transitions driven by correlations. These topological phases can form only for a small range of twist angles around the magic angle, which further differentiates them from the Landau levels observed near charge neutrality. Moreover, we observe that even the charge-neutrality Landau spectrum taken at low fields is considerably modified by interactions, exhibits prominent electron–hole asymmetry, and features an unexpectedly large splitting between zero Landau levels (about 3 to 5 millielectronvolts). Our results show how strong electronic interactions affect the MATBG band structure and lead to correlation-enabled topological phases.

Item Type:Article
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URLURL TypeDescription ReadCube access Paper
Kim, Hyunjin0000-0001-9886-0487
Peng, Yang0000-0002-8868-2928
Thomson, Alex0000-0002-9938-5048
Polski, Robert0000-0003-0887-8099
Zhang, Yiran0000-0002-8477-0074
Arora, Harpreet Singh0000-0002-7674-735X
Watanabe, Kenji0000-0003-3701-8119
Alicea, Jason0000-0001-9979-3423
Nadj-Perge, Stevan0000-0002-2916-360X
Alternate Title:Correlation-driven Topological Phases in Magic Angle Twisted Bilayer Graphene, Tracing out Correlated Chern Insulators in Magic Angle Twisted Bilayer Graphene
Additional Information:© 2021 Nature Publishing Group. Received 21 August 2020; Accepted 13 November 2020; Published 18 January 2021. We acknowledge discussions with A. Young, G. Refael and S. Mashhadi. The device nanofabrication was performed at the Kavli Nanoscience Institute (KNI) at Caltech. This work was supported by NSF through grants DMR-2005129 and DMR-1723367 and by the Army Research Office under grant award W911NF-17-1-0323. Part of the initial STM characterization was supported by CAREER DMR-1753306. Nanofabrication performed by Y.Z. was supported by the DOE-QIS programme (DE-SC0019166). J.A. and S.N.-P. also acknowledge the support of IQIM (an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through grant GBMF1250). Y.P. acknowledges support from a startup fund from California State University, Northridge. A.T., C.L. and J.A. are grateful for support from the Walter Burke Institute for Theoretical Physics at Caltech and the Gordon and Betty Moore Foundation’s EPiQS Initiative, grant GBMF8682. Y.C. and H.K. acknowledge support from the Kwanjeong fellowship. Data availability: The data that support the findings of this study are available from the corresponding authors on reasonable request. These authors contributed equally: Youngjoon Choi, Hyunjin Kim. The authors declare no competing interests. Peer review information: Nature thanks Vincent Renard, Yayu Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Group:Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics, Kavli Nanoscience Institute
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0323
Department of Energy (DOE)DE-SC0019166
Institute for Quantum Information and Matter (IQIM)UNSPECIFIED
Gordon and Betty Moore FoundationGBMF1250
California State University, NorthridgeUNSPECIFIED
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Gordon and Betty Moore FoundationGBMF8682
Kwanjeong Educational FoundationUNSPECIFIED
Subject Keywords:Electronic properties and materials; Phase transitions and critical phenomena
Issue or Number:7843
Record Number:CaltechAUTHORS:20200922-103631989
Persistent URL:
Official Citation:Choi, Y., Kim, H., Peng, Y. et al. Correlation-driven topological phases in magic-angle twisted bilayer graphene. Nature 589, 536–541 (2021).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105469
Deposited By: Tony Diaz
Deposited On:22 Sep 2020 17:45
Last Modified:16 Nov 2021 18:43

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