Exciton-polaritons offer a versatile platform for realization of all-optical integrated logic gates due to the strong effective optical nonlinearity resulting from the exciton-exciton interactions. In most of the current excitonic materials there exists a direct connection between the exciton robustness to thermal fluctuations and the strength of exciton-exciton interaction, making materials with highest levels of exciton nonlinearity applicable at cryogenic temperatures only. Here, we show that strong polaronic effects, characteristic for perovskite materials, allow to overcome this limitation. Namely, we demonstrate the recordhigh value of the nonlinear optical response in nanostructured organic-inorganic halide perovskite MAPbI 3 , experimentally detected as 19.7 meV blueshift of the polariton branch under femtosecond laser irradiation. This is substantially higher than characteristic values for the samples based on conventional semiconductors and monolayers of transition metal dichalcogenides. The observed strong polaron-enhanced nonlinearity exists for both tetragonal and orthorombic phases of MAPbI 3 , and remains stable at elevated temperatures.

Systems supporting exciton-polaritons represent solid-state optical platforms with a strong built-in optical nonlinearity provided by exciton-exciton interactions. In conventional semiconductors with hydrogen-like excitons the nonlinearity rate demonstrates the inverse scaling with the binding energy. This makes excitons stable at room temperatures weakly interacting, which obviously limits the possibilities of practical applications of the corresponding materials for nonlinear photonics. We demonstrate experimentally and theoretically, that these limitations can be substantially softened in hybrid perovskites, such as MAPbBr 3 due to the crucial role of the polaron effects mediating the inter-particle interactions. The resulting exciton-polaron-polaritons remain both stable and strongly interacting at room temperature, which is confirmed by large nonlinear blueshifts of lower polariton branch energy under resonant femtosecond laser pulse excitation. Our findings open novel perspectives for the management of the exciton-polariton nonlinearities in ambient conditions.