Ultrafast femtosecond laser control of electron dynamics in two-dimensional strong spin-orbit coupling materials

利用基于麦克斯韦-TDDFT格式的时变密度泛函理论（TDDFT），利用经典麦克斯韦方程和时变Kohn-Sham （TDKS）方程的组合来描述电磁场的传播。针对过渡金属二硫族化物二维层中的超快电子动力学，通过单色和双色激光场研究了WSe2单层中谷极化载流子动力学。谷选择规则表明，线偏振光对谷和谷极化都是相等的，而线偏振光场不能实现谷极化。我的研究集中在上述论点上，我们的目标是通过线极化脉冲诱导谷不对称，这被认为是线极化场无法实现的。通过混合基频和二次谐波可以产生非对称激光场。两脉冲强度比和相对载波包络相位（CEP）控制了谷极化。将双色激光方案的谷偏振结果与单色脉冲的谷偏振结果进行了比较。我发现，通过双色控制的谷偏振超过单色方案的1.2倍，因为双色场在时间形状上表现出更多的不对称性。结果为谷假自旋的光学控制提供了一条方便的新途径。

By using Time-dependent density functional theory (TDDFT) based on the Maxwell-TDDFT scheme, the combined classical Maxwell plus time-dependent Kohn-Sham (TDKS) equations are used to describe the propagation of electromagnetic fields. Regarding the ultrafast electron dynamics in 2D layers of Transition metal dichalcogenides, I investigated the carrier dynamics in terms of valley polarization in WSe2 monolayer via single and two-color laser field.The valley selection rules suggest that linearly polarized light couples equally to both valleys and valley polarization cannot be achieved by a linearly polarized field. My study is focused on the above-mentioned argument and we aimed to induce valley asymmetry by linearly polarized pulses which are considered not achievable by a linearly polarized field.It is possible to create an asymmetric laser field by mixing a fundamental frequency and its second harmonic. The two pulses intensity ratio and the relative carrier-envelope phase (CEP) control the valley polarization. I compared the valley polarization results of two-color laser scheme results with the single color pulse. I found that the valley polarization via two-color control exceeds the single-color scheme by 1.2 times as the two-colors field exhibits more asymmetry in its temporal shape. The results reveal a convenient new path toward the optical control of valley pseudospins.