A free-exciton gas is studied as a function of generated particle density in ${\mathrm{Cu}}_2$O at 1.5 K. A line-shape analysis of the subsequent recombination shows a gradual evolution, from a classical regime at low density, to a highly quantum-statistical one with chemical potential $\mu \simeq 0$.

• Received 9 April 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1970