Fig. 5: Dark exciton interaction and relaxation paths.

a Scheme of the energy levels and possible transitions among different exciton species. The transition DI shown with dash lines indicates the scattering D⁰ → I⁰ that occurs only for high values of exciton kinetic energy. b Calculated exciton density at the steady state as a function of the generation rate for the excitonic states illustrated in (a). c The strong interaction of D⁰ at the excitation position provides initial momentum to propagate uphill. The transported hot dark excitons can then thermalize toward the bottom of their energy dispersion via scattering with low energy Γ acoustic phonons. From this state, they can radiatively recombine in the form of a dark exciton D⁰, dark trions D⁻, phonon replica \({D}_{p}^{-}\), T₁, or I⁰.