First-order spatial coherence of excitons in planar nanostructures: Ak-filtering effect

Abstract

We propose and analyze a k∥-filtering effect which gives rise to the drastic difference between the actual spatial coherence length of quasi-two-dimensional excitons or microcavity polaritons in planar nanostructures and that inferred from far-field optical measurements. The effect originates from conservation of the in-plane wave-vector k∥ in the optical decay of the particles in outgoing bulk photons. The k∥-filtering effect explains the large coherence lengths recently observed for indirect excitons in coupled quantum wells but is less pronounced for microcavity polaritons at low temperatures, T≲10 K.