Twist Angle Dependent Ultrafast Transient Dynamics of MoSe$_2$/WSe$_2$ van der Waals Heterostructures beyond the Exciton Mott Transition

TL;DR

This study investigates how twist angle influences ultrafast charge dynamics in MoSe2/WSe2 heterostructures at high excitation densities, revealing minimal recombination times at specific commensurate angles and implications for optoelectronic device design.

Contribution

It provides new insights into twist-angle dependent ultrafast dynamics and non-radiative recombination processes in TMD heterostructures beyond the Mott transition.

Findings

Recombination time is minimized at commensurate angles.

Non-radiative Auger recombination strength is lowest at these angles.

Additional relaxation channels are present near commensurate angles.

Abstract

Two-dimensional van der Waals heterostructures (HS) exhibit twist-angle ($\theta$) dependent interlayer charge transfer, driven by moir\'e potential that tunes the electronic band structure with varying $\theta$. 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.