Ultrafast optical control of multivalley states in two-dimensional 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 multivalley 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 subcycle, ultrafast switching among multiple valley states. These findings provide further insight into valley dynamics in 2D materials and may contribute to future developments in valleytronics applications.