Strong spin-orbit coupling effect induced large valley splitting in Janus MSeXH (M = Cr, Mo, and W; X = N and P).

Exploring valley physics in two-dimensional materials with strong spin-orbit coupling is significant in fundamental physics. In this work, we demonstrated that the two-dimensional (2D) MSeXH family (M = Cr, Mo, and W; X = N and P) includes promising 2D valley materials based on first-principles calculations. We found that monolayer MSeXH exhibited large valley splitting, and monolayer WSePH exhibited the highest value of 495 meV. This was mainly owing to the strong spin-orbital coupling effect and built-in vertical E-field in the Janus structure. Valley splitting remained under biaxial strain from -4% to 4%, and monolayer (1L) MoSeNH exhibited a relatively high carrier mobility. Furthermore, the Berry curvature at the valence band maximum and its relationship with the valley Hall effect were analysed. The computational results confirmed that the material exhibited good mechanical and dynamic stability. This work provides a promising family of 2D valleytronic materials for practical applications in valley electronics.