Suppression of molecule formation for orthoexciton-polaritons in Cu₂O

The lifetime of dense orthoexcitons in Cu₂O is severely limited by dark molecule formation. In order to investigate this two-body process for orthoexciton-polaritons, we employ two-photon excitation and resonantly create orthoexciton-polaritons at 2 K, which are the coherent quantum superposition of orthoexcitons and the light field. Based on the steady-state analysis, we find that this density-dependent process is an order of magnitude reduced for resonantly created orthoexciton-polaritons compared with thermalized orthoexcitons at 2 K. This most likely arises from the photonic character of an orthoexciton-polariton. Considering the greatly reduced effective mass of the orthoexciton-polariton, this implies that the experimentally achievable orthoexciton-polariton densities can be above the critical density for Bose-Einstein condensation. However, insufficient elastic scattering seems to keep this propagating quantum ensemble from internal equilibrium.