Twist-Angle-Dependent Ultrafast Transient Dynamics of MoSe2/WSe2 van der Waals Heterostructures beyond the Exciton Mott Transition

Abstract

Two-dimensional van der Waals heterostructures (HS) exhibit twist-angle (θ)-dependent interlayer charge transfer, driven by moiré potential that tunes the electronic band structure with varying θ. Apart from the magic angles of ∼3° and ∼57.5° that show flat valence bands (twisted WSe₂ bilayer), the commensurate angles of 21.8° and 38.2° reveal the Umklapp light coupling of interlayer excitons. We report our results on nondegenerate optical pump–optical probe spectroscopy of MoSe₂/WSe₂ HS at large twist angles under high photoexcitation densities above the Mott transition threshold, generating interlayer localized charge carriers. We show that the recombination time of electrons and holes is minimum at commensurate angles. The strength of nonradiative interlayer Auger recombination also shows a minimum at the commensurate angles. The fluence dependence of the interlayer carrier recombination time suggests additional relaxation channels near the commensurate angles. This study emphasizes the significance of the large twist angle of HS in developing transition-metal dichalcogenide-based optoelectronic devices.