Angular distribution of photoluminescence as a probe of Bose Condensation of trapped excitons

TL;DR

This paper demonstrates that the angular distribution of photoluminescence can serve as a diagnostic tool for detecting Bose condensation and vortices in trapped exciton systems, revealing coherence and phase fluctuations.

Contribution

It introduces a method to identify Bose condensation in excitons through changes in PL angular distribution and visualizes vortex configurations via interference patterns.

Findings

Bose condensation causes a sharply focused PL peak normal to the plane.

Temperature affects the PL peak due to phase fluctuations.

Vortex configurations create interference nodes in the PL distribution.

Abstract

Recent experiments on two-dimensional exciton systems have shown the excitons collect in shallow in-plane traps. We find that Bose condensation in a trap results in a dramatic change of the exciton photoluminescence (PL) angular distribution. The long-range coherence of the condensed state gives rise to a sharply focussed peak of radiation in the direction normal to the plane. By comparing the PL profile with and without Bose Condensation we provide a simple diagnostic for the existence of a Bose condensate. The PL peak has strong temperature dependence due to the thermal order parameter phase fluctuations across the system. The angular PL distribution can also be used for imaging vortices in the trapped condensate. Vortex phase spatial variation leads to destructive interference of PL radiation in certain directions, creating nodes in the PL distribution that imprint the vortex configuration.