Two-dimensional materials are known to possess emergent properties that are not found in their bulk counterparts. Recent experiments have shown a $sqrt7 times sqrt3$ charge density wave (CDW) in monolayer 1T-VSe2, in contrast to the $4times 4times 3$ phase in bulk. In this work, via first-principles calculations, we show that multiple CDW phases compete in monolayer VSe2, and the ground state of which can be tuned by charge doping and in-plane biaxial strain. With doping, phase transitions occur from the $sqrt7 times sqrt3$ CDW of the pristine VSe2 to a $3 times sqrt3$ and to a $4times 4$ phase, which is a projection from the bulk counterpart, at critical doping concentrations of around 0.2 hole per formula unit and 0.25 electron per formula unit, respectively. The $4times 4$ CDW phase can also be stabilized under compressive strain. The phase transitions can be well understood by Fermi surface nesting. These results make VSe2 an appealing material for electronic devices based on controllable CDW phase transitions.
Published in: "arXiv Material Science".