Moiré exciton condensate: nonlinear Dirac point, broken-symmetry Bloch waves and unusual optical selection rules

Abstract

Moiré exciton features tunable Dirac dispersion and spatially dependent optical selection rules. With the long lifetime due to its interlayer nature, it is promising to realize a Bose-Einstein condensation of moiré excitons. Here we study the properties of moiré exciton condensate within the mean-field theory, with special focus on exciton-exciton interaction effect on the nonlinear Bloch band and Bloch waves of exciton condensate in moiré potential. We find the nonlinear dispersion of the moiré exciton condensate exhibits complex loop structure induced by exciton-exciton interaction. A nonlinear Dirac cone emerges at $\mathbf{\Gamma }$ point of the Bloch band, with a three-fold degenerate nonlinear Dirac point. Each degenerate Bloch wave at nonlinear Dirac point spontaneously breaks $C3$ rotational symmetry of the moiré potential, and themselves differ by $C3$ rotations. Since they reside in the light cone, these nontrivial Bloch band structure and broken-symmetry Bloch waves can be experimentally detected by examining light emission from those states. Symmetry breaking of Bloch states implies unusual optical selection rules compared with single exciton case: moiré exciton condensate at $\mathbf{\Gamma }$ point emits light with all three components of polarization instead of only left or right circular polarization. We further propose that, by applying in-plane electric field on one layer to drive an initially optically dark exciton condensate towards light cone, the light polarization of final states as well as their dependence on field direction serves as the smoking gun for experimental observation.

7 pages, 6 figures. Comments are welcome

References in corpus (9)

• Observation of Moiré Excitons in WSe2/WS2 Heterostructure Superlattices
• Resonantly hybridised excitons in moiré superlattices in van der Waals heterostructures
• Moiré excitons: from programmable quantum emitter arrays to spin-orbit coupled artificial lattices
• Evidence of high-temperature exciton condensation in 2D atomic double layers
• Moiré heterostructures as a condensed matter quantum simulator
• Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers
• Nonlinear Dirac Cones
• Nonlinear Bloch-waves and current states of exciton-polariton condensates
• Twist versus heterostrain control of optical properties of moiré exciton minibands

Cited by in corpus (2)

• Review: Advanced characterization of the spatial variation of moiré heterostructures and moiré excitons
• Searching for Unconventional Superfluid in Excitons of Monolayer Semiconductors