A Caltech Library Service

Tracing out Correlated Chern Insulators 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 (2020) Tracing out Correlated Chern Insulators in Magic Angle Twisted Bilayer Graphene. . (Unpublished)

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


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,±3 electrons occupy each moiré unit cell and lead to the formation of correlated insulating, superconducting and ferromagnetic phases. While some phases have been shown to carry a non-zero Chern number, the local microscopic properties and topological character of many other phases remain elusive. Here we introduce a set of novel techniques hinging on scanning tunneling microscopy (STM) to map out topological phases in MATBG that emerge in finite magnetic field. By following the evolution of the local density of states (LDOS) at the Fermi level with electrostatic doping and magnetic field, we visualize a local Landau fan diagram that enables us to directly assign Chern numbers to all observed phases. We uncover the existence of six topological phases emanating from integer fillings in finite fields and whose origin relates to a cascade of symmetry-breaking transitions driven by correlations. The spatially resolved and electron-density-tuned LDOS maps further reveal that these topological phases can form only in a small range of twist angles around the magic-angle value. Both the microscopic origin and extreme sensitivity to twist angle differentiate these topological phases 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 and exhibits an unexpected splitting between zero Landau levels that can be as large as ∼3−5 meV. Our results show how strong electronic interactions affect the band structure of MATBG and lead to the formation of correlation-enabled topological phases.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription 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
Additional Information:We acknowledge discussions with Andrea Young, Gil Refael and Soudabeh Mashhadi. The device nanofabrication was performed at the Kavli Nanoscience Institute (KNI) at Caltech. Funding: 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 has been supported by CAREER DMR-1753306. Nanofabrication performed by Y.Z. has been supported by DOE-QIS program (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). 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. Author Contribution: Y.C. and H.K. fabricated samples with the help of with the help of R.P., Y.Z., and H.A., and performed STM measurements. Y.C., H.K., and S.N.-P. analyzed the data. Y.P. and A.T. implemented models. Y.P., A.T., C.L., provided theoretical analysis supervised by J.A. . K.W. and T.T. provided materials (hBN). S.N-P supervised the project. Y.C, H.K, Y.P., A.T., C.L., J.A. and S.N-P wrote the manuscript. Data availability: The data that support the findings of this study are available from the corresponding authors on reasonable request.
Group:Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics
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
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Gordon and Betty Moore FoundationGBMF8682
Kwanjeong Educational FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20200922-103631989
Persistent URL:
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:22 Sep 2020 17:45

Repository Staff Only: item control page