Robust Moire Exciton Coherence in a Twisted MoSe2 Bilayer

Moire superlattices provide a versatile platform to engineer many-body excited states in atomically thin semiconductors. Transition metal dichalcogenides (TMDs) are known host exciton resonances with large oscillator strength, and thus, rapidly radiative decays. While exciton quantum dynamics in TMD monolayers and natural bilayers are found to be determined by exciton radiative decay and phonon-assisted valley scatterings, respectively, quantum dynamics of moire excitons have never been experimentally investigated. 

Here, we study a twisted MoSe2 bilayer with a small twist angle from the near-H stacking style. The homogeneous linewidth or the dephasing time of moire excitons is measured using two-dimensional electronic coherence spectroscopy (2DCES) and compared with a MoSe2 monolayer. Although the homogeneous linewidth of the moire exciton is broader than that of monolayer excitons at low temperatures, it is remarkably robust against temperature increases. This temperature-independent exciton coherence is unexpected and likely arises from a modified exciton–phonon interaction in moire superlattices.