Exciton Steering via Potential Landscape Engineered by Excited Electron-Hole Phase Transition

Controlling exciton transport-especially intralayer excitons with strong light-matter interactions-is challenging due to the lack of efficient, tunable driving mechanisms, hindering practical excitonic device development. In this Letter, we demonstrate all-optical steering of intralayer excitons in monolayer MoS_{2} through optically driven, highly excited excitonic phase transitions. Combining spatial emission, microscopic theory, and drift-diffusion modeling, we show that spatial screening from high-excitation phase transitions generates exciton binding energy gradients, driving excitons toward higher binding energy regions. The engineered screening profile creates an energy landscape that drives excitons and unbound electrons and holes in opposite directions. This counterflow, enabled by their distinct responses, can be optically switched via the exciton-Mott transition. Our findings disentangle the transport mechanisms of excitons and unbound electrons and holes, demonstrating that excitons in 2D semiconductors propagate as cohesive quasiparticles, while free carriers move along band edges. This enables all-optical control of photocarrier transport and provides a new approach to engineer energy landscapes, paving the way for reconfigurable excitonic interconnects and quantum optical devices.