Mobile-Immobile model for exciton diffusion in 2D semiconductors

Excitons in low-dimensional semiconductors  diffuse, get trapped and eventually released by defects and recombine with a photon emission (photoluminescence). Modern experimental methods allow good precision measurements of the photoluminescence both locally  as well as overall. This allows to plot the distributions of the densities of immobile (non-trapped) excitons as a function of time as well a integral characteristics. The experiments reveal a ew interesting an non-trivial effects including the power-law tails o photoluminescence intensity and observable backward (or negative) diffusion. For the explanation we propose and study the mobile-immobile model which splits the population into two groups, the mobile and the immobile particles. The interplay of these two subpopulations explains varios experiments quite well.