Modeling of the thermalization of trapped paraexcitons in Cu2O at ultralow temperatures

We theoretically analyze the relaxation of paraexcitons in cuprous oxide due to exciton- phonon and excitonexciton scattering. Particular attention is paid to the evolution of the distribution function as well as to the cooling process of the exciton gas. The results underline the importance of interexcitonic collisions at moderate and higher densities which prevent the formation of the typical bottleneck and accelerate the thermalization at ultralow temperatures significantly. Furthermore, we discuss the impact of strain on the exciton-phonon coupling and show that the overall cooling process of the excitons benefits from strain induced effects. However, for very low lattice temperatures (T << 1.0 K), the process of thermalization is slow, and the excitons might not reach the lattice temperature within their finite lifetime.