Tuning electronic and magnetic properties of early transition-metal dichalcogenides via tensile strain

We have performed a systematic first-principles study of the effect of tensile strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX₂ (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, Te). Our density functional theory calculations suggest that the tensile strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX₂, ZrX₂, HfX₂), the bandgap increases with the tensile strain, but for ZrX₂ and HfX₂ (X = S, Se), the bandgap starts to decrease at strain 6-8%. For the group VB TMDCs (TaX ₂), the tensile strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group VIB TMDCs (CrX₂), the direct-to-indirect bandgap transition is seen upon application of the tensile strain, except CrTe₂ whose bandgap decreases with the tensile strain even though the direct character of its bandgap is retained. Lastly, for the group IIIB TMDCs (ScX₂) in the T metallic phase, we find that the tensile strain has little effect on their electronic and magnetic properties. Our study suggests that strain engineering is an effective approach to modify electronic and magnetic properties of most early TMDC monolayers, thereby opening an alternative way for future optoelectronic and spintronic applications.