Multiple Topological Phases with Electronic Correlation in Intrinsic Ferromagnetic Semimetal VI3 Monolayer

Abstract

2D topological materials with magnetic ordering have become hot topics due to their nontrivial band topology and quantum states. In this work, the second-order topological states and evolution of linear band crossing are successfully predicted utilizing the effective k· p and tight binding models in the intrinsic ferromagnetic VI₃ monolayer under various effective Hubble interaction U_eff. Upon inclusion of spin orbit coupling, a small bandgap (E_g-1) of 12.7 meV is opened with a Chern invariant C = −1 at U_eff = 0 eV. The E_g-1 undergoes a transition from the non-trivial state to trivial state at U_eff = 0.80 eV, accompanied by the appearance of Dirac cone. Remarkably, the increase of U_eff causes the band inversion and adjustment of crystal symmetry, resulting in two unreported coexisting topological bandgaps (E_g-2 and E_g-3). Furthermore, a gapless node-loop appears at U_eff = 1.06 eV and disappears at U_eff = 1.09 eV around Γ point. Moreover, for the first time, the existence of second-order topological states with quantized corner fractional charges (e/3) is also observed in the VI₃ monolayer at U_eff ≥0.96 eV. These results make the VI₃ monolayer a compelling candidate for exploring topological devices.