Microcavity polariton kinetics for bosonic condensation and lasing in II-VI compound materials

Abstract

We investigate with a Boltzmann approach the relaxation kinetics of II-VI compound microcavity polaritons after a nonresonant pump pulse for the example of CdTe. In these polar materials large vacuum Rabi microcavity splittings guarantee robust polariton modes in the strong-coupling regime with an extremely small effective mass at the bottom of the lower branch, but with very short cavity lifetimes. Our kinetic treatment for stationary and picosecond-pulsed pumping takes the polariton--acoustic-phonon as well as the polariton-polariton scattering into account. For cavities with a vacuum Rabi splitting around $\ensuremath{\Omega}=10\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, we find for nonresonant picosecond-pulse excitation a relaxation scenario which leads to a transient bosonic condensation in the lowest polariton state and coherent laser action at densities smaller than the exciton saturation density. For microcavities with a large vacuum Rabi splitting of $\ensuremath{\Omega}=26\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ we find due to the steep increase of radiative losses and the simultaneous steep decrease of the scattering rates with decreasing energy a nonequilibrium phase transition with a macroscopically occupied state in the bottleneck region at a finite transverse momentum and a connected coherent laser emission under an angle of 17\ifmmode^\circ\else\textdegree\fi{}. All of our results for medium and large Rabi vacuum splitting are in good qualitative agreement with corresponding observations of Dang and co-workers