Electron-magnon coupling and quasiparticle lifetimes on the surface of a topological insulator

Abstract

The fermionic self-energy on the surface of a topological insulator proximity coupled to ferroand antiferromagnetic insulators is studied. An enhanced electron-magnon coupling is achieved by allowing the electrons on the surface of the topological insulator to have a different exchange coupling to the two sublattices of the antiferromagnet. Such a system is therefore seen as superior to a ferromagnetic interface for the realization of magnon-mediated superconductivity. The increased electron-magnon-coupling simultaneously increases the self-energy effects. A careful study of this has been lacking, and in this paper we show how the inverse quasiparticle lifetime and energy renormalization on the surface of the topological insulator can be kept low close to the Fermi level by using a magnetic insulator with a sufficient easy-axis anisotropy. We find that the antiferromagnetic case is most interesting both from a theoretical and an experimental standpoint due to the increased electron-magnon coupling, combined with a reduced need for easy-axis anisotropy compared to the ferromagnetic case. We also consider a set of material and instrumental parameters where these selfenergies should be measurable in angle-resolved photoemission spectroscopy (ARPES) experiments, paving the way for a measurement of the interfacial exchange coupling strength.