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

TL;DR

This paper introduces a k-filtering effect that explains the significant difference between the actual spatial coherence length of quasi-2D excitons or polaritons in nanostructures and the lengths inferred from optical measurements, highlighting the impact of wavevector conservation.

Contribution

The paper presents the concept of a k-filtering effect that accounts for discrepancies in measured versus actual coherence lengths in planar nanostructures.

Findings

k-filtering effect causes large observed coherence lengths in indirect excitons

Effect is less significant for microcavity polaritons at low temperatures

Explains recent experimental observations of exciton coherence

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 (quasi-2D) excitons or microcavity (MC) polaritons in planar nanostructures and that inferred from far-field optical measurements. The effect originates from the conservation of in-plane wavevector 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 (QWs), but is less pronounced for MC polaritons at low temperatures, T<10K.