Prediction of switchable half semiconductor in d¹ transition metal dichalcogenide monolayers

We propose that a half semiconducting state can exist in trigonal-prismatic transition metal dichalcogenide (TMDC) monolayers of d¹ configuration. In that state both electrons and holes are spin polarized and share the same spin channel. On the basis of hybrid density functional theory, we predict in particular that VS₂ monolayers are half semiconductors with a direct band gap. Moreover, we find that the conduction electron spin orientation of VS₂ switches under moderate strain. Our predictions thus open up intriguing possibilities for applications of VS₂ in spintronics and optoelectronics. Our analysis of trigonal-prismatic group-V MX₂ (M=V, Nb, Ta; X=S, Se, Te) monolayers reveals a broad diversity of electronic states that can be understood qualitatively in terms of localization of d electrons.