Excitonic density wave and spin-valley superfluid in bilayer transition metal dichalcogenide

Zhen Bi () and Liang Fu ()
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Zhen Bi: Massachusetts Institute of Technology
Liang Fu: Massachusetts Institute of Technology

Nature Communications, 2021, vol. 12, issue 1, 1-10

Abstract: Abstract Artificial moiré superlattices in 2d van der Waals heterostructures are a new venue for realizing and controlling correlated electronic phenomena. Recently, twisted bilayer WSe2 emerged as a new robust moiré system hosting a correlated insulator at moiré half-filling over a range of twist angle. In this work, we present a theory of this insulating state as an excitonic density wave due to intervalley electron–hole pairing. We show that exciton condensation is strongly enhanced by a van Hove singularity near the Fermi level. Our theory explains the remarkable sensitivity of the insulating gap to the vertical electric field. In contrast, the gap is weakly reduced by a perpendicular magnetic field, with quadratic dependence at low field. The different responses to electric and magnetic field can be understood in terms of pair-breaking versus non-pair-breaking effects in a BCS analog of the system. We further predict superfluid spin transport in this electrical insulator, which can be detected by optical spin injection and spatial-temporal imaging.

Date: 2021
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DOI: 10.1038/s41467-020-20802-z

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