Ultrafast coherent dynamics of optically inactive excitons in semiconductors

The center-of-mass momentum distribution of optically created excitons in semiconductors is known to be constrained by the (very small) light momenta at times immediately following the excitation, and it is governed by incoherent scattering processes on longer time scales. The present theoretical analysis suggests that, on intermediate time scales, nonlinear mean-field interactions between excitons lead to a coherent, wave-like evolution in the momentum distribution of optically inactive excitons. Proposals for possible experimental verification of these predictions are discussed.