Ultrafast field-driven valley polarization in TMDC quantum dots

We study theoretically interaction of circularly polarized ultrashort and ultrafast optical pulse with transition metal dichalcogenide (TMDC) quantum dots. Quantum dots are described within an effective model and have a shape of a disk. The duration of the pulse is a few femtoseconds, and the electron dynamics in the field of such pulse is coherent. We study the valley polarization generated after a circularly polarized pulse. The valley polarization is defined as the difference in conduction band populations of the K and K' valleys of TMDC quantum dots. The valley polarization depends both on the size of the dot, i.e., its radius, and on the amplitude of the pulse field. The valley polarization decreases with increasing the size of the dot. Such dependence can be related to the dependence of the quantum dot bandgap on the radius of the dot. The valley polarization of a TMDC quantum dot has nonmonotonic dependence on the field amplitude, where the maximum valley polarization is realized at a finite field amplitude around 0.1 V/A.