Quantum spin liquid dynamics

The excitation spectra of topological phases of matter contain rather `direct' information about their unusual quasiparticles, while the corresponding bulk ground states tend to be rather featureless. Motivated by this observation, we have evaluated the dynamical structure factor of the Kitaev model on the honeycomb lattice, which is unusual in that it hosts a family of spin liquids amenable to exact analysis. We find that the structure factor contains direct evidence of fractionalisation, in the form of both Majorana fermions and emergent gauge fluxes. It can be probed in experiments such as neutron scattering or Raman spectroscopy. As these are subject to different selection rules, they reveal complementary information. We discuss the situation on the experimental front, in particular on the 'proximate spin liquid' in $\alpha$-RuCl$_3$.