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

Abstract

Artificial moiré superlattices in 2d van der Waals heterostructure is a new venue for realizing and controlling correlated electronic phenomena. Recently, twisted bilayer WSe${}_2$ 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.

arXiv comment10 pages, 8 figures. To appear in Nature Communications

Cited by in corpus (6)

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• Spin-valley locked instabilities in moire transition metal dichalcogenides with conventional and higher-order Van Hove singularities
• Moiré induced topology and flat bands in twisted bilayer WSe${}_2$: A first-principles study
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