THRESHOLD BEHAVIOR IN THE COLLISION BROADENING OF MICROCAVITY POLARITONS

The problem of the density-dependent homogeneous broadening of microca vity polaritons due to exciton-exciton Coulomb interaction is addresse d using the self-consistent Born approximation. The theoretical result s predict that, for resonant pumping of the lower polariton, the depen dence of its broadening on the density of excitations has a threshold behavior. Below the threshold density, scattering is strongly inhibite d because it involves only the small region of k space where the polar iton effective mass is very light. Above threshold, the region of k sp ace with excitonlike dispersion becomes allowed, giving the dominant c ontribution to the collision broadening. [S0163-1829(98)52740-3].