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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 (2019) Recovery of massless Dirac fermions at charge neutrality in strongly interacting twisted bilayer graphene with disorder. . (Unpublished) https://resolver.caltech.edu/CaltechAUTHORS:20191216-103049254

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Abstract

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, multi-domain samples exhibit re-emergent massless Dirac fermions formed by gapless domain-wall modes, yielding semimetallic behavior except on the ultra-long 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:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/1910.11348arXivDiscussion Paper
ORCID:
AuthorORCID
Alicea, Jason0000-0001-9979-3423
Additional Information: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 W911NF-17-1-0323; the NSF through grant 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 GBMF1250; the Walter Burke Institute for Theoretical Physics at Caltech; and the Gordon and Betty Moore Foundation’s EPiQS Initiative, Grant GBMF8682 to JA. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611.
Group:UNSPECIFIED, Institute for Quantum Information and Matter, Walter Burke Institute for Theoretical Physics
Funders:
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0323
NSFDMR-1723367
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
NSFPHY-1607611
Record Number:CaltechAUTHORS:20191216-103049254
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191216-103049254
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100297
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 Dec 2019 20:52
Last Modified:04 Jun 2020 10:14

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