The possibility to observe a macroscopically coherent state in a gas of two-dimensional direct excitons at temperatures up to tens of Kelvin is described. The dramatic increase of the exciton lifetime allowing effective thermalization is predicted for the o_-resonant cavities that strongly suppress exciton recombination. The material systems considered are single GaAs quantum wells of different thicknesses and a transition metal dichalcogenide monolayer, embedded in a layered medium with subwavelength period. The quantum hydrodynamic approach combined with the Bogoliubov description yield the one-body density matrix of the system. Employing the Kosterlitz-Thouless “dielectric screening” problem to account for vortices, we obtain the superfluid and the condensate densities and the critical temperature of the Berezinskii-Kosterlitz-Thouless crossover, for all geometries in consideration. Experimentally observable many fold increase of the photoluminescence intensity from the structure as it is cooled below the critical temperature is predicted.
The reported work describes different regimes of exciton-polariton oscillatory dynamics in a microcavity, in the conservative case as well as in the presence of continuous-wave pumping from the high-energy excitonic reservoir. Accounting for exciton-photon energy detuning, linear and non-linear decay, gain, and interactions, we discuss the influence of different ingredients of the system on the dynamics in conservative and non-conservative cases, and show the existence of non-trivial regimes reminiscent of internal Josephson effect, van der Pol oscillations, and the inverted Kapitza pendulum. Conditions of experimental observation of the predicted effects are considered.
The properties of traps for exciton polaritons in a semiconductor optical microcavity with an embedded quantum well were considered. The two-component Bose condensate of photons and excitons was described by a coupled system of equations similar to the Gross-Pitaevskii equations, and analytical solutions in the Thomas-Fermi approximation were obtained for traps with weak exciton confinement. For strong confinement, condensate behavior was investigated numerically, and spatial profiles of coupled condensates of excitons and photons (which appear to be different in general case) were determined.