GdN thin film: Chern insulating state on square lattice

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Using first-principles calculations, we predict a Chern insulating phase in thin films of the ferromagnetic semimetal GdN. In contrast to previously proposed Chern insulator candidates, which mostly rely on honeycomb lattices, this system affords a great chance to realize the quantum anomalous Hall effect on a square lattice without either a magnetic substrate or transition metal doping, making synthesis easier. The band inversion between the $5d$ orbitals of Gd and $2p$ orbitals of N is verified by first-principles calculations based on density functional theory, and the band gap can be as large as 100 meV within the GdN trilayer. With a further increase of film thickness, the band gap tends to close and the metallic bulk property becomes obvious.