Kerr, Faraday, and magnetoelectric effects in MnBi2Te4 thin films

The topological magnetoelectric effect (TME) is a characteristic property of topological insulators. In this paper, we use a simplified coupled-Dirac-cone electronic structure model to theoretically evaluate the THz and far infrared Kerr and Faraday responses of thin films of MnBi2Te4 with up to N = 10 septuple layers with the goal of clarifying the relationship between these convenient magnetooptical observables and the TME. We find that for even N, the linear Kerr and Faraday responses to an electric field vanish in the low-frequency limit, even though the magnetoelectric response is large and approximately quantized.