Polariton-polariton interactions in microcavities under a resonant 10 to 100 picosecond pulse excitation

Experimental studies have been performed of the nonequilibrium transitions in multistable cavity-polariton systems under 10 ps long pulsed excitation, i.e., within nearly the shortest time scale necessary for the multistability to be revealed in GaAs-based microcavities. The experiments were aimed to determine the ratio of the strengths of the pair interactions between polaritons with parallel and antiparallel spins, which also was the question raised in a number of recent studies. We show that in contrast to the cases of continuous-wave or nanosecond long pumping conditions, in the fast pulse regime the system is not affected by the excitonic reservoir. The interaction between polaritons with opposite spins is definitely attractive at a nearly zero detuning of exciton and photon modes; as a result, optical response can be essentially multistable at a linearly polarized excitation. With increasing pulse duration up to 100 ps, the reservoir can start manifesting itself in a reduction of the spin multistability.