Electrical Control of Valley Polarized Charged Exciton Species in Monolayer WS 2 .

Excitons are key to the optoelectronic applications of van der Waals semiconductors, with the potential for versatile on-demand tuning of properties. Yet, their electrical manipulation remains challenging due to inherent charge neutrality and the additional loss channels induced by electrical doping. We demonstrate the dynamic electrical control of valley polarization in charged excitonic states of monolayer tungsten disulfide, achieving up to a 6-fold increase in the degree of circular polarization under off-resonant excitation. In contrast to the weak direct tuning of excitons typically observed using electrical gating, the charged exciton photoluminescence remains stable, even with increased scattering from electron doping. By exciting at the exciton resonances, we observed the reproducible nonmonotonic switching of the charged state population as the electron doping is varied under gate bias, indicating a resonant interplay between neutral and charged exciton states.