Twist Angle Dependent Ultrafast Transient Dynamics of MoSe$_2$/WSe$_2$ van der Waals Heterostructures beyond the Exciton Mott Transition
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 $\sim$3$^\circ$ and $\sim$57.5$^\circ$ that show flat valence bands (twisted WSe$_2$ bilayer), the commensurate angles of 21.8$^\circ$ and 38.2$^\circ$ reveal the Umklapp light coupling of interlayer excitons. We report our results on non-degenerate optical pump-optical probe spectroscopy of MoSe$_2$/WSe$_2$ 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 the commensurate angles. The strength of non-radiative interlayer Auger recombination also shows a minimum at the commensurate angles. The fluence dependence of 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 dichalcogenides-based optoelectronic devices.