Femtosecond switching of strong light-matter interactions in 2D semiconductor microcavities

Hybridization between inter- and intralayer excitons can occur in Transition Metal Dichalcogenide (TMD) bilayers, giving rise to dipolar excitons with high oscillator strength. Such excitons can be exploited to achieve high optical nonlinearities, when TMDs are strongly coupled to light confined in optical microcavities. However, observations of TMD polaritons ultrafast temporal dynamics and their exploitation remain elusive. We performed pump-probe spectroscopy experiments at 8K in a custom-made microscope to study hBN-encapsulated monolayers and bilayers of MoS2 placed in optical microcavities. We probe the ultrafast dynamics of exciton-polaritons in such systems by resonantly exciting the cavities with femtosecond pulses and measuring the transient differential reflectivity. Our experiments revealed an ultrafast sub-picosecond switching from strong to weak coupling regime with a fast reversible recovery, and we demonstrated its high frequency operation (250 GHz) as an optical switch. The rich dynamics of TMD polaritons explored in our work give access to extreme nonlinear phenomena in TMD systems on ultrafast time scales for future optical logic gates.