Revealing of Dark Exciton States by Twisted Light in Two Dimensional Transition Metal Dichalcogenides

Brightening spin- and momentum-forbidden dark exciton in two-dimensional (2D) transition metal dichalcogenides (TMDs) is nontrivial to further advances in optoelectronics applications. In this study, we demonstrate the effects of the interaction between twisted light (light possessing orbital angular momentum) and atomically thin TMD material in the optical measurements. Our results show a reproducible blue shift in the photoluminescence (PL) spectra of both monolayer and bilayer TMD material as the topological charge of the illuminating twisted light is incremented along positive and negative values. This phenomenon is attributed to the transfer of orbital angular momentum from twisted light onto the center-of-mass momentum of excitons which consequently brightens momentum-forbidden dark exciton states. Further, based on the observation on power-dependence of PL spectra, we found a red shift with increasing laser power across different topological charge values of the incident light. It reveals that there is another factor such as heat or strain induced by twisted light, which can replace the dominant mechanism. This study uncovers a new selection rule in 2D TMD materials that can potentially be a useful control mechanism for future optoelectronic device applications.