Resonant Brillouin Scattering of Polaritons in ZnSe: Heavy and Light Excitons

This Letter reports the first experimental observation of heavy and light excitons by resonant Brillouin scattering of polaritons in ZnSe. The number of the Brillouin peaks as well as their variations with the excitation light energy are well accounted for on the basis of a three-branch polariton dispersion curve in which the longitudinal-transverse splitting $E_{\mathrm{LT}}$ and the exchange energy $\Delta$ mix both kinds of excitons. The observation of the three branches allows us to determine $E_{\mathrm{LT}}$, $\Delta$, and the translational masses $M_h$ and $M_1$ of heavy and light excitons.