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Recovery of massless Dirac fermions at charge neutrality in strongly interacting twisted bilayer graphene with disorder

Thomson, Alex and Alicea, Jason (2021) Recovery of massless Dirac fermions at charge neutrality in strongly interacting twisted bilayer graphene with disorder. Physical Review B, 103 (12). Art. No. 125138. ISSN 2469-9950. doi:10.1103/PhysRevB.103.125138.

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Stacking two graphene layers twisted by the magic angle θ≈1.1∘ generates flat energy bands, which in turn catalyzes various strongly correlated phenomena depending on filling and sample details. At charge neutrality, transport measurements reveal superficially mundane semimetallicity (as expected when correlations are weak) in some samples yet robust insulation in others. We propose that the interplay between interactions and disorder admits either behavior, even when the system is strongly correlated and locally gapped. Specifically, we argue that strong interactions supplemented by weak, smooth disorder stabilize a network of gapped quantum valley Hall domains with spatially varying Chern numbers determined by the disorder landscape—even when an entirely different order is favored in the clean limit. Within this scenario, sufficiently small samples that realize a single domain display insulating transport characteristics. Conversely, multidomain samples exhibit re-emergent massless Dirac fermions formed by gapless domain-wall modes, yielding semimetallic behavior except on the ultralong scales at which localization becomes visible. We discuss experimental tests of this proposal via local probes and transport. Our results highlight the crucial role that randomness can play in ground-state selection of twisted heterostructures, an observation that we expect to have further ramifications at other fillings.

Item Type:Article
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URLURL TypeDescription Paper
Thomson, Alex0000-0002-9938-5048
Alicea, Jason0000-0001-9979-3423
Additional Information:© 2021 American Physical Society. Received 15 November 2019; revised 23 October 2020; accepted 30 November 2020; published 17 March 2021. We are grateful to Cory Dean, Arbel Haim, Eslam Khalaf, Stevan Nadj-Perge, Felix von Oppen, Seth Whitsitt, and Andrea Young for illuminating discussions. This work was supported by the Army Research Office under Grant Award No. W911NF-17-1-0323; the NSF through Grant No. DMR-1723367; the Caltech Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant No. GBMF1250; the Walter Burke Institute for Theoretical Physics at Caltech; and the Gordon and Betty Moore Foundation's EPiQS Initiative, Grant No. GBMF8682 to J.A. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation Grant No. PHY-1607611.
Group:Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0323
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
Issue or Number:12
Record Number:CaltechAUTHORS:20191216-103049254
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100297
Deposited By: Tony Diaz
Deposited On:16 Dec 2019 20:52
Last Modified:21 Apr 2021 17:04

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