Anisotropic exciton diffusion in atomically-thin semiconductors

Abstract

Abstract Energy transport processes are critical for the efficiency of many optoelectronic applications. The energy transport in technologically promising transition metal dichalcogenides is determined by exciton diffusion, which strongly depends on the underlying excitonic and phononic dispersion. Based on a fully microscopic theory we demonstrate that the valley-exchange interaction leads to an enhanced exciton diffusion due to the emergence of a linear excitonic dispersion and the resulting decreased exciton-phonon scattering. Interestingly, we find that the application of a uniaxial strain can drastically boost the diffusion speed and even give rise to a pronounced anisotropic diffusion, which persists up to room temperature. We reveal that this behaviour originates from the highly anisotropic exciton dispersion in the presence of strain, displaying parabolic and linear behaviour perpendicular and parallel to the strain direction, respectively. Our work demonstrates the possibility to control the speed and direction of exciton diffusion via strain and dielectric engineering. This opens avenues for more efficient and exotic optoelectronic applications of atomically thin materials.