A magnetic topological insulator in two-dimensional EuCd₂Bi₂: giant gap with robust topology against magnetic...

Magnetic topological states open up exciting opportunities for exploring fundamental topological quantum physics and innovative design of topological spintronics devices. However, the nontrivial topologies, for most known magnetic topological states, are usually associated with and may be heavily deformed by fragile magnetism. Here, using a tight-binding model and first-principles calculations, we demonstrate that a highly robust magnetic topological insulator phase, which remains intact under both ferromagnetic and antiferromagnetic configurations, can emerge in two-dimensional EuCd₂Bi₂ quintuple layers. Because of spin-orbital coupling, an inverted gap with intrinsic band inversions occuring simultaneously for up and down spin channels is obtained, accompanied by a nonzero spin Chern number and a pair of gapless edge states, and remarkably the magnitude of the nontrivial band gap for EuCd₂Bi₂ reaches as much as 750 meV. Moreover, the robustness of the magnetic TI phase is further confirmed by rotating the magnetization directions, indicating that EuCd₂Bi₂ represents a promising material for understanding and utilizing the topological insulating states in two-dimensional spin-orbit magnets.