Majorana spectroscopy of 3D Kitaev spin-liquids

TL;DR

This paper investigates the dynamical response of 3D Kitaev quantum spin-liquids with different low-energy Majorana fermion spectra, revealing distinct features in the dynamical structure factor and implications for neutron scattering experiments.

Contribution

It provides a detailed analysis of the dynamical structure factor in 3D Kitaev spin-liquids with various Majorana spectra, extending the understanding of their spectral signatures and experimental probes.

Findings

Distinct dynamical responses for Fermi surfaces, nodal lines, and Weyl points.

Connection between low-energy response and density of states or phase shifts.

Rich high-energy fine-structure determined by microscopic Majorana spectrum features.

Abstract

We analyse the dynamical response of a range of 3D Kitaev quantum spin-liquids, using lattice models chosen to explore the different possible low-energy spectra for gapless Majorana fermions, with either Fermi surfaces, nodal lines or Weyl points. We find that the behaviour of the dynamical structure factor is distinct in all three cases, reflecting the quasiparticle density of states in two fundamentally different ways. First, the low-energy response is either straightforwardly related to the power with which the low-energy density of states vanishes; or for a non-vanishing density of states, to the phase shifts encountered in the corresponding X-ray edge problem, whose phenomenology we extend to the case of Majorana fermions. Second, at higher energies, there is a rich fine-structure, determined by microscopic features of the Majorana spectrum. Our theoretical results test the usefulness of inelastic neutron scattering as a probe of these quantum spin liquids: we find that although spin flips fractionalise, the main features of the dynamical spin response nevertheless admit straightforward interpretations in terms of Majorana and flux loop excitations.