Real Chern Insulator in Monolayer Decorated Transition Metal Nitrides

Abstract A trend in recent research is to push the study of topological phases to the spin‐splitting antiferromagnetic (SSAFM) systems, which has become a research forefront of spintronics. Here, the realization of SSAFM real Chern insulator (RCI) in the monolayer transition metal nitride A(BN) ₂ (A = Mg, Ca, Zn and B = Co) is revealed. Taking monolayer Mg(CoN) ₂ (ML‐MgCoN) as an example. In the absence of spin‐orbit coupling, the ML‐MgCoN is an altermagnetic (AM) material, and each spin channel of the material possesses a nontrivial real Chern number protected by symmetry. Unlike conventional RCIs, the multi‐atomic‐layer structure and altermagnetism of ML‐MgCoN lead to the emergence of two sets of corner states exhibiting opposite layer and spin polarizations. Under out‐of‐plane electric field ( E _z ) and uniaxial strain, the ML‐MgCoN is no longer an AM material but still a SSAFM material with symmetry in each spin channel. Moreover, the degeneracy of the two sets of topological corner states is lifted, suggesting a selective control of layer and spin polarizations under external fields. This work not only significantly broadens the material database of AM RCI, but also reveals a new mechanism to control the spin in spintronics.