Ultrafast spatial hole burning of excitonic emission in monolayer WS₂

The transport of excitons lies at the heart of excitonic devices. Probing, understanding, and manipulating excitonic transport represents a critical step prior to their technological applications. In this work, we report experimental studies on the ultrafast nonlinear transport of excitons in monolayer WS₂. Under intense optical pumping, we observe an ultrafast spatial hole burning effect in the excitonic emission profile, followed by a re-brightening at even higher pumping density. Through time- and spatially-resolved photoluminescence spectroscopy, we reveal the underlying mechanism responsible for these nontrivial excitonic diffusion dynamics. Our results demonstrate that the combined effects of ultrafast exciton-exciton annihilation, efficient hole trapping by intrinsic sulfur vacancy defects, and laser-induced photo-oxidation govern the evolution of exciton transport under strong optical excitation. The observed dynamics are in excellent agreement with our diffusion model simulations, providing new insights into the nonlinear excitonic transport behaviors as well as their optical control mechanism in two-dimensional semiconductors.