A first-principles study of the phase stability and electronic properties of monolayer Vanadium-based Janus dichalcogenides

We investigate the vibrational and electronic properties of 2D van der Waals Vanadium-based Janus dichalcogenides (VSSe, VSeTe, VSTe) at the monolayer level in both 2H and 1T phases by using first-principles calculations. We have found the 2H phase is energetically favorable in VSSe and VSeTe, whereas the 1T phase is lower in energy in VSTe. Within density functional theory, ferromagnetism (FM) allows splitting of the d-bands in the 2H phase with a trigonal prismatic environment, leading to a low-bandgap S=1/2 ferromagnetic insulator. On the other hand, no such splitting is observed in the distorted octahedral environment of the 1T phase, and the system remains metallic. In the presence of electronic correlations, we have found the magnetic ground state is FM for VSSe and VSeTe. On the contrary, a 120^o canted AFM state is the magnetic ground state for VSTe. The semiconducting nature of FM two-dimensional Janus VSSe and VSeTe makes them potential materials for spintronics.