Tunable magnetic topological insulating phases in monolayer CrI3

We present results indicating that Chern insulator states can be achieved in the recently synthesized pristine chromium triiodide (CrI3) by either electron or hole doping. Our first-principles density-functional-theory calculations confirmed that monolayer CrI3 show nontrivial Chern number C in both the valence and conduction bands. By introducing on-site Coulomb interaction or epitaxial strain, the doped CrI3 exhibit a series of topological quantum phase transitions between multiple Chern insulator phases as well as semimetal-to-insulator transitions. We show that the covalency of Cr d-I p bands controlled by the on-site Coulomb interaction U and strain is one of the key ingredients determining the topological phase and semimetal-insulator phase boundary.