Ultrafast Optical Control of Multi-Valley States in 2D SnS

We theoretically study the ultrafast optical control of multiple valley states in two‐dimensional (2D) tin sulfide (SnS) monolayers, a member of the layered group-IV monochalcogenides, which is a promising class of materials for overcoming current challenges in valleytronics. By combining time‐dependent density functional theory with Maxwell’s equations, we simulate how both linearly and circularly polarized ultrashort laser pulses affect the electronic excitation dynamics and valley polarization in SnS. Our results reveal that the corrugated phosphorene like crystal structure of SnS monolayers leads to the emergence of both linear and circular dichroism, allowing flexible manipulation of multi-valley excitation by simply adjusting the light polarization. Moreover, the interplay between broken inversion symmetry and spin-orbit coupling gives rise to distinct Berry curvature effects and spin valley coupling, thereby enabling circular dichroism. Furthermore, we propose that tuning the carrier‐envelope phase of few-cycle femtosecond laser pulses can achieve sub‐cycle, ultrafast switching among multiple valley states. These findings not only deepen our understanding of valley dynamics in 2D materials but may also open new avenues for the development of valleytronic devices.