Enhancement of valley selective excitation by a linearly polarized two-color laser pulse

Abstract

Here we proposed the valley selective excitations via a two-color (\ensuremath{\omega} + \ensuremath{2\omega}) laser field, made by superimposing two linearly polarized pulses at frequencies \ensuremath{\omega} and \ensuremath{2\omega}. We have studied the intensity ratio between a few-cycle pulse of \ensuremath{\omega} and \ensuremath{2\omega} laser, and its enhancement factor by employing the time-dependent first-principle calculations. The valley polarization depends on the carrier envelope phases (CEPs) of pulses and the intensity ratio $I_{\omega}/I_{2\omega}$. We found that the two-color field enhances the valley polarization as much as 1.2 times larger than the single-color pulse. The maximum valley asymmetry is achieved for the intensity ratio $I_{\omega}/I_{2\omega}$ of 36 with the relative CEP of \ensuremath{\pi}. In our previous work, we found that the asymmetric vector potential induces the valley polarization (Phys. Rev. B 105,115403 (2022)). In this work, we find that the asymmetry of the electric field modulates the valley polarization. Our two-color scheme offers a new path toward the optical control of valley pseudospins. \end{abstract}