Optical signatures of interlayer electron coherence in a bilayer semiconductor

Atomically-thin transition metal dichalcogenides (TMDs) provide a highly tunable platform for many-body interactions and strongly correlated phenomena, including Mott insulators, generalized Wigner crystals and excitonic insulators. Here we investigate excitonic interactions in homobilayer MoS₂​, a system known for hosting interlayer excitons (IXs) with large out-of-plane dipoles. By studying the quantum-confined Stark effect of the IXs and their interactions with additional charges, we observe unusual hybridization between IXs with opposing dipoles, distinct from both conventional level crossing and anti-crossing behaviors. We show that the observations can be explained by stochastic coupling between the excitons, which increases with electron density and decreases with temperature. Our findings suggest the emergence of an order parameter in the form of interlayer electron coherence under conditions when electron tunneling between the layers is negligible.