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Abstract Emergent strongly correlated electronic phenomena in atomically thin transition-metal dichalcogenides are an exciting frontier in condensed matter physics, with examples ranging from bilayer superconductivity and electronic Wigner crystals to the ongoing search for exciton condensation. Here we take a step towards the latter by reporting experimental signatures of unconventional hybridization of the excitons with opposing dipoles consistent with coherence between interlayer electrons in a transition-metal dichalcogenide bilayer. We investigate naturally grown MoS₂homobilayers integrated in a dual-gate device structure allowing independent control of the electron density and out-of-plane electric field. By electron doping the bilayer when electron tunnelling between the layers is negligible, we observe that the two interlayer excitons hybridize, displaying unusual behaviour distinct from both conventional level crossing and anti-crossing. We show that these observations can be explained by quasi-static random coupling between the excitons, which increases with electron density and decreases with temperature. We argue that this phenomenon is indicative of a spatially fluctuating order parameter in the form of interlayer electron coherence, a theoretically predicted many-body state that has yet to be unambiguously established experimentally outside of the quantum Hall regime. 

Abstract Techniques to mold the flow of light on subwavelength scales enable fundamentally new optical systems and device applications. The realization of programmable, active optical systems with fast, tunable components is among the outstanding challenges in the field. Here, we experimentally demonstrate a few-pixel beam steering device based on electrostatic gate control of excitons in an atomically thin semiconductor with strong light-matter interactions. By combining the high reflectivity of a MoSe₂monolayer with a graphene split-gate geometry, we shape the wavefront phase profile to achieve continuously tunable beam deflection with a range of 10°, two-dimensional beam steering, and switching times down to 1.6 nanoseconds. Our approach opens the door for a new class of atomically thin optical systems, such as rapidly switchable beam arrays and quantum metasurfaces operating at their fundamental thickness limit.