Doping induced multiferroicity and quantum anomalous Hall effect in -In₂Se₃ thin films

In flatband materials, the strong Coulomb interaction between electrons can lead to exotic physical phenomena. Recently, alpha-In2Se3 thin films were found to possess ferroelectricity and flat bands. In this work, using first-principles calculations, we find that for the monolayer, there is a Weyl point at Gamma in the flatband, where the inclusion of the spin-orbit coupling opens a gap. Shifting the Fermi level into the spin-orbit gap gives rise to nontrivial band topology, which is preserved for the bilayer regardless of the interlayer polarization couplings. We further calculate the Chern number and edge states for both the monolayer and bilayer, for which the results suggest that they become quantum anomalous Hall insulators under appropriate dopings. Moreover, we find that the doping-induced magnetism for the In2Se3 bilayer is strongly dependent on the interlayer polarization coupling. Therefore, doping the flat bands in In2Se3 bilayer can also yield multiferroicity, where the magnetism is electrically tunable as the system transforms between different polarization states. Our study, thus, reveals that multiferroicity and nontrivial band topology can be unified into one material for designing multifunctional electronic devices.