Spin-induced valley polarization in heterobilayer Janus transition-metal dichalcogenides

Abstract

Inspired by potential application prospects of the spintronics and valleytronics, a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in original bilayer MoS2. Based on first-principles calculation, it is found that SMoS/SeMoS structure exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime. The transition metal (TM) atom represented by V/Cr/Mn can be stably adsorbed on the heterobilayer Janus SMoS/SeMoS sheet and effectively introduce magnetic moments (m). The calculation results demonstrate that the most stable adsorption site of TM atom is CX(A), and the TM (V/Cr/Mn) adatom modified SMoS/SeMoS system is converted into metal (V-) or half-metal (Cr/Mn-), respectively. Under the coupling of different indirect exchange interactions, the structure exhibits stable intrinsic anti-ferromagnetic (AFM) for V-SMoS/SeMoS and ferromagnetic (FM) ground state for Cr/Mn-SMoS/SeMoS, respectively, and the magnetic transition temperature (Tc) reaches high temperature or even room temperature. Moreover, the robust out-of-plane magnetocrystalline anisotropy energy (MAE) ensures stable long-range magnetic order. Specifically, the combination of spin injection and strong spin-orbit coupling (SOC) interaction effectively breaks the time-reversal symmetry, leading to valley polarization of the system. Based on this, the biaxial strain can effectively regulate the electronic structure, magnetic properties and valley polarization of TM-SMoS/SeMoS nanosheets with double broken of spatial-inversion and time-reversal symmetry.