Stimulated Exciton–Polariton Scattering in Hybrid Halide Perovskites

Halide perovskites such as methylammonium lead bromide (MAPbBr₃) host tightly bound three-dimensional excitons that are robust at room temperature. The excellent optical properties of MAPbBr₃ allow the design of optical single-mode waveguides and cavities in the frequency range close to excitonic transitions. Taken together, these results indicate that MAPbBr₃ is an excellent platform for probing exciton–polariton nonlinear phenomena at room temperature. Here, we investigate the ultrafast nonequilibrium dynamics of polaritons under nonresonant femtosecond-pulsed excitation. We demonstrate the presence of a stimulated acoustic phonon-assisted scattering regime above the threshold pump fluence, characterized by the explosive growth of emission intensity, a redshift of the emission spectral maximum, spectral narrowing, and subpicosecond emission dynamics. Our theoretical findings are confirmed by experimental measurements.