Stimulated polariton-polariton scattering and dynamic Bose-Einstein condensation of polaritons in GaAs microcavities under excitation near the exciton resonance

The dynamics of formation of the macroscopically occupied polariton mode at the bottom of the polariton band $E_{LP}(k=0)$ and its spin polarization under the quasiresonant pulse excitation of excitons ($E = E_X$) with large values of quasi-momentum have been studied in planar GaAs microcavities. It has been found that the growth in the depth $E_X -E_{LP}(k=0)$ of the polariton band leads to the change in the formation mechanism for the $k = 0$ condensate state from the direct parametric decay of the photoexcited mode (due to the polariton-polariton interaction) to the dynamic condensation of polaritons, which results from the multiple scattering of polaritons by both phonons and polaritons. At the same time, in microcavities with $E_X-E_{LP}(k=0)>3.5$ meV, the direct decay of the photoexcited mode does not disappear, becoming an efficient mechanism for the filling of the states located at the $k$-space ring, corresponding to the energies $E_{LP}(\mathbf k) \approx E_X -2.6$ meV.