Transient Microscopy of Mobile Excitons in 2D Semiconductors

Transport of optical excitations in semiconducting solids plays a central role from both fundamental and technological perspectives. In systems with strong Coulomb interaction the propagation of optically injected carriers is dominated by excitons instead of free electrons or holes. These correlations can affect both the overall energy landscape and the interactions with vibrational modes, with a strong impact on the mobility of the excitations.<br/>In this talk I will discuss recent studies employing the technique of transient microscopy to monitor propagation of mobile exciton quasiparticles in two-dimensional van der Waals semiconductors. In these systems, the electron-hole correlations present a particularly interesting case combining the properties of Wannier-Mott excitations in inorganic quantum well systems with high exciton binding energies that are more characteristic for Frenkel-like states in molecular crystals. I will discuss linear and non-linear phenomena, influence of environmental screening and disorder, and present strategies to externally manipulate exciton propagation. I will outline the limits of semi-classical and hopping transport in monolayer semiconductors and illustrate the impact of free charge carriers on the exciton diffusion.