Interlayer excitons in bilayer MoS2 with strong oscillator strength up to room temperature

Coulomb bound electron-hole pairs, excitons, govern the optical properties of transition metal dichalcogenides (TMDs) like MoS2 and WSe2. TMD bilayers allow studying several exciton species : intralayer excitons with electrons and holes in the same layer and also interlayer excitons with the electron and the hole residing in different layers.
In this combined experimental and theoretical work we report on the observation of interlayer excitons in a high quality homobilayer MoS2 sample encapsulated in hexagonal boron nitride (hBN). The interlayer exciton transition is located between the intralayer A and B excitons and is observable in reflectivity between 4 and 300 K, whereas no such transition is observed for the monolayer in the same structure in this energy range. Our peak attribution is supported by DFT calculations solving the Bethe-Salpeter equation after GW bandstructure calculations. We find in the calculated absorption spectrum a strong, spin allowed transition situated in energy between A and B intralayer excitons stemming from an electron residing on one and the hole residing in the other layer, both at the K-point of the Brillouin zone. We discuss the possibility of hybridization of exciton species and compare with our results on homotrilayer MoS2.