Coherence properties and luminescence spectra of condensed polaritons in CdTe microcavities

TL;DR

This paper investigates the coherence properties and luminescence spectra of polariton condensates in CdTe microcavities, providing theoretical estimates and analyzing experimental data to understand their behavior and phase transition thresholds.

Contribution

It offers a theoretical analysis of coherence lengths, spectral features, and the effects of detuning on polariton condensation in microcavities, connecting theory with recent experiments.

Findings

Thermal coherence length estimated at ~5 micrometers.

Exponential decay of temporal coherence matches experimental observations.

Dispersionless region in luminescence spectra at small momenta around 4 degrees.

Abstract

We analyse the spatial and temporal coherence properties of a two-dimensional and finite sized polariton condensate with parameters tailored to the recent experiments which have shown spontaneous and thermal equilibrium polariton condensation in a CdTe microcavity [J. Kasprzak, M. Richard, S. Kundermann, A. Baas, P. Jeambrun, J.M.J. Keeling, F.M. Marchetti, M.H. Szymanska, R. Andre, J.L. Staehli, et al., Nature 443 (7110) (2006) 409]. We obtain a theoretical estimate of the thermal length, the lengthscale over which full coherence effectively exists (and beyond which power-law decay of correlations in a two-dimensional condensate occurs), of the order of 5 micrometers. In addition, the exponential decay of temporal coherence predicted for a finite size system is consistent with that found in the experiment. From our analysis of the luminescence spectra of the polariton condensate, taking into account pumping and decay, we obtain a dispersionless region at small momenta of the order of 4 degrees. In addition, we determine the polariton linewidth as a function of the pump power. Finally, we discuss how, by increasing the exciton-photon detuning, it is in principle possible to move the threshold for condensation from a region of the phase diagram where polaritons can be described as a weakly interacting Bose gas to a region where instead the composite nature of polaritons becomes important.