Bose-Einstein condensation of excitons in ${\mathrm{Cu}}_2\mathrm{O}$

We present a parameter-free model that estimates the density of excitons in ${\mathrm{Cu}}_2\mathrm{O},$ related to experiments that have tried to create an excitonic Bose-Einstein condensate. Our study demonstrates that the triplet-state excitons move along adiabats and obey classical statistics, while the singlet-state excitons are a possible candidate for forming a Bose-Einstein condensate. Finally we show that the results of this study do not change qualitatively in a two-dimensional exciton gas, which can be realized in a quantum well.