  The photoluminescence dynamics of a microscopic gas of indirect excitons
trapped in coupled quantum wells is probed at very low bath temperature
(approximately 350 mK). Our experiments reveal the non linear energy relaxation
characteristics of indirect excitons. Particularly, we observe that the
excitons dynamics is strongly correlated with the screening of structural
disorder by repulsive exciton-exciton interactions. For our experiments where
two-dimensional excitonic states are gradually defined, the distinctive
enhancement of the exciton scattering rate towards lowest energy states with
increasing density does not reveal unambiguously quantum statistical effects
such as Bose stimulation.
