Room-Temperature Polaron-Mediated Polariton Nonlinearity in MAPbBr3 Perovskites

Systems supporting exciton-polaritons represent solid-state optical platforms with a strong built-in optical nonlinearity provided by exciton-exciton interactions. In conven-tional semiconductors, with hydrogen-like excitons, the non-linearity rate demonstrates the inverse scaling with the binding energy. This makes excitons that are stable at room temperature 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 perov-skites, such as MAPbBr3, due to the crucial role of the polaron effects mediating the interparticle 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.