Valley-Controlled Many-Body Exciton Interactions in Monolayer WSe₂ Phototransistors.

via valley-selective excitation using polarization-resolved pulsed-laser photocurrent spectroscopy. Circular excitation selectively populates excitons in a single valley, whereas linear excitation populates both valleys, inducing a valley-dependent nonlinear photoresponse. We observe helicity-dependent exciton renormalization, alongside a 2-fold enhancement of sublinear photocurrent scaling under circular excitation, reflecting a single-valley population of interacting excitons. A microscopic model incorporating intervalley-exchange and exciton-exciton annihilation mediated by dark and bright exciton populations reproduces the nonlinear valley-selective response. These results establish the valley degree of freedom as an all-optical control parameter for tuning many-body excitonic effects and exploring correlated exciton states and valleytronic applications in two-dimensional semiconductors.