Spin dynamics and lifetime of exciton polaritons in CuCl

In CuCl, biexcitons may be excited from the semiconductor ground state by two circularly polarized exciton polaritons of opposite helicity. We use this property to develop a new method in order to determine the spin-relaxation dynamics by means of non-degenerate pump-probe experiments. A pump beam first excites a spin-polarized exciton population. Then, we measure the induced absorption of a circularly polarized probe beam at the exciton biexciton transition. It depends on its polarization and the induced absorption dynamics gives information on the spin state of the exciton polariton population. When comparing results obtained in a (σ+σ+) configuration with that of a (σ+σ−) configuration, we determine the time evolution of the pseudo-spin of the exciton polaritons as well as their lifetime.