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

TL;DR

This paper investigates how electron-magnon interactions affect quasiparticle lifetimes on the surface of topological insulators when coupled with magnetic insulators, highlighting conditions for measurable effects and potential for magnon-mediated superconductivity.

Contribution

It introduces a method to enhance electron-magnon coupling on topological insulator surfaces using antiferromagnetic insulators with easy-axis anisotropy, enabling measurable self-energy effects.

Findings

Antiferromagnetic coupling increases electron-magnon interaction.

Low quasiparticle lifetime effects can be maintained near the Fermi level.

Self-energy effects are detectable via angle-resolved photoemission spectroscopy.

Abstract

The fermionic self-energy on the surface of a topological insulator proximity coupled to ferro- and 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. 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 from both 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 self-energies should be measurable in angle-resolved photoemission spectroscopy experiments, paving the way for a measurement of the interfacial exchange coupling strength.