Valley pseudospin in monolayer Mo Si2N4 and Mo Si2As4

For a long time, two-dimensional (2D) hexagonal MoS₂ was proposed as a promising material for the valleytronic system. However, the limited size of growth and low carrier mobility in MoS₂ restrict its further application. Very recently, a new kind of hexagonal 2D MXene, Mo Si₂N₄ , was successfully synthesized with large size, excellent ambient stability, and considerable hole mobility. In this paper, based on first-principles calculations, we predict that the valley-contrasting properties can be realized in monolayer Mo Si₂N₄ and its derivative Mo Si₂As₄ . Beyond the traditional two-level valleys, the valleys in monolayer Mo Si₂As₄ are multiple folded, implying another valley dimension. Such multiple-folded valleys can be described by a three-band low-power Hamiltonian. This study presents the theoretical advance and the potential applications of monolayer Mo Si₂N₄ and Mo Si₂As₄ in valleytronic devices, especially multiple information processing.