Continuous Control and Enhancement of Excitonic Valley Polarization in Monolayer WSe2 by Electrostatic Doping

Enhancement and continuous control of the excitonic valley polarization in electrostatically doped monolayer WSe2 are demonstrated. Under excitation with circularly polarized light, 20% valley polarization of excitons around the charge neutrality condition at 70 K is increased to 40% by modulating the electron/hole density up to 2 × 1012 cm−2. This increase originates from slow valley relaxation for neutral exciton between the K and −K valleys owing to screening of long‐range e–h exchange interactions by doped carriers. The gate‐dependences of the exciton valley polarization at various temperatures are reproduced by theoretical calculations, which holds potential for next‐generation valleytronic devices continuously controlled by an applied bias voltage.