Evidence for Bose-Einstein condensation of a two-component exciton gas

Abstract

Time-resolved spectral and spatial measurements of photoluminescence in ${\mathrm{Cu}}_2$O at low temperatures suggest that the gas of paraexcitons undergoes Bose-Einstein condensation at high densities. As a result of the two-component nature of the gas (orthoexcitons and paraexcitons with different ground-state energies and spin multiplicities) and the nonequilibrium nature of photoproduced excitons, the condensation process is quite different from the simple ideal-gas case envisioned by Einstein.