Layer dipole magnetoelectric polarizability of antiferromagnetic bilayers

Abstract: In this paper we study magnetoelectric effects in two-dimensional magnetic bilayers and introduce the notion of a layer dipole magnetoelectric polarizability. This magnetoelectric polarizability describes the magnetization response to an applied electric field perpendicular to the bilayer. As such, it represents the electric analog of the spin magnetoelectric polarizability, governing the charge polarization response to an applied Zeeman field. Starting from the orbital magnetization produced by a perpendicular displacement field, we derive a microscopic expression for the layer dipole magnetoelectric polarizability and apply it to two minimal models for bilayer magnets, i.e., a buckled square lattice model and a magnetic topological insulator model. In the case of the buckled square lattice model we show that the layer dipole magnetoelectric polarizability has a (quasi-)topological contribution, revealing a topological magnetoelectric response of two-dimensional antiferromagnets associated with the layer pseudospin degree of freedom.