Spin-dependent high-order topological states and corner modes in a monolayer FeSe/GdClO heterostructure

We propose that a spin-dependent second-order topological insulator can be realized in a monolayer FeSe/GdClO heterostructure, in which substrate GdClO helps to stabilize and enhance the antiferromagnetic order in FeSe. The second-order topological insulator is free from spin-orbit coupling and in-plane magnetic field. We also find that two types of distinct corner modes residing in the intersections of two ferromagnetic edges and two antiferromagnetic edges exist. The underlying physics for the ferromagnetic corner mode follows a sublattice-chirality-kink picture. More interestingly, the ferromagnetic corner mode shows a spin-dependent property, which is also robust against spin-orbit coupling. Unexpectedly, the antiferromagnetic corner mode can be taken as a typical emergent and hierarchical phenomenon from an array of ferromagnetic corner modes. Remarkably, antiferromagnetic corner modes violate the general kink picture and can be understood as bound states of a one-dimensional Schrodinger equation under a connected potential well. Our findings not only provide a promising second-order topological insulator in electronic materials but also uncover some different properties of corner modes in high-order topological insulators.