Resonant Raman scattering theory for Kitaev models and their Majorana fermion boundary modes

TL;DR

This paper analyzes the resonant Raman scattering response in 2D and 3D Kitaev spin-liquid models, revealing how boundary modes are detectable in certain symmetry classes and how symmetry breaking affects the response.

Contribution

It provides a detailed calculation of the resonant Raman/Brillouin scattering vertex for Kitaev models, highlighting differences in boundary mode detection across symmetry classes BDI and D.

Findings

Resonant scattering can detect boundary modes in BDI class thin films.

Non-resonant processes do not couple to boundary modes in BDI.

Coupling to surface states is suppressed in D class systems.

Abstract

We study the inelastic light scattering response in two- (2D) and three-dimensional (3D) Kitaev spin-liquid models with \ms band structures in the symmetry classes BDI and D leading to protected gapless surface modes. We present a detailed calculation of the resonant Raman/Brillouin scattering vertex relevant to iridate and ruthenate compounds whose low-energy physics is believed to be proximate to these spin-liquid phases. In the symmetry class BDI, we find that while the resonant scattering on thin films can detect the gapless boundary modes of spin liquids, the non-resonant processes do not couple to them. For the symmetry class D, however, we find that the coupling between both types of light-scattering processes and the low-energy surface states is strongly suppressed. Additionally, we describe the effect of weak time-reversal symmetry breaking perturbations on the bulk Raman response of these systems.