Many-body correlations of electrostatically trapped dipolar excitons

We study the photoluminescence (PL) of a two-dimensional liquid of oriented dipolar excitons in InₓGa_1-xAs coupled double quantum wells confined to a microtrap. Generating excitons outside the trap and transferring them at lattice temperatures down to $T=240$ mK into the trap we create cold quasiequilibrium bosonic ensembles of some 1000 excitons with thermal de Broglie wavelengths exceeding the excitonic separation. With decreasing temperature and increasing density n5×10¹⁰0.222222em0ex1cm² we find an increasingly asymmetric PL line shape with a sharpening blue edge and a broad red tail which we interpret to reflect correlated behavior mediated by dipolar interactions. From the PL intensity $I(E)$ below the PL maximum at E₀ we extract at $T<5$ K a distinct power law I(E)~(E₀-E)^-|α| with -|α|≈-0.8 in the range E₀-E of 1.5--4 meV, comparable to the dipolar interaction energy.