Exciton transport in atomically flat heterostructures: The appearance of negative diffusivity

Quasiparticles in semiconductors reveal different regimes of propagation. Here we theoretically analyze phonon-assisted transport of excited quasiparticles in two-dimensional systems by means of a quasi-classical kinetic equation in the presence of relaxation and local uniform force field in the vicinity of the one-dimensional interface formed by two different atomically flat materials stitched together. We analyze the dynamics of excitons and focus on the situation when initial exciton density distribution is optically excited directly at the interface of two atomically flat materials. We considered both homogeneous and inhomogeneous cases, when identical and different diffusion coefficients for materials are present. The appearance of negative diffusivity was revealed in both cases. Moreover, mean-squared displacement was studied for various system parameters, and different behavior was observed in short- and long-time domains.