Enhanced Polariton Interactions in Suspended WS Monolayer Microcavity.

Transition-metal dichalcogenides monolayers exhibit strong exciton resonances that enable intense light-matter interactions. The sensitivity of these materials to the surrounding environment and their interactions with the substrate result in the enhancement of excitonic losses through scattering, dissociation and defects formation, hindering their full potential for the excitation of optical nonlinearities in exciton-polariton platforms. The use of suspended monolayers holds the potential to completely eliminate substrate-induced losses, offering unique advantages for the exploitation of intrinsic electronic, mechanical, and optical properties of 2D materials-based polaritonic systems, without any influence of proximity effects. In this work, we report a novel fabrication approach enabling the realization of a planar microcavity filled with a suspended tungsten disulfide (WS) monolayer in its center. We experimentally demonstrate a 2-fold enhancement of the strong coupling at room temperature, due to the larger exciton binding energy and reduced overall losses as compared to similar systems based on dielectric-filled microcavities. As a result, spin-dependent polaritonic interactions are significantly amplified, leading to achievement of a record exciton interaction constant approaching the theoretically predicted value. This approach holds promises for pushing 2D materials-based polaritonic systems to their intrinsic limits, paving the way for the realization of novel polaritonic devices with superior performance.