Dynamics of a two-dimensional quantum spin-orbital liquid: spectroscopic signatures of fermionic magnons

TL;DR

This paper provides an exact analysis of dynamical correlations in a quantum spin-orbital liquid on a honeycomb lattice, revealing spectroscopic signatures of fermionic magnons that can be experimentally observed.

Contribution

It offers an exact theoretical description of spin dynamics in a SU(2)-symmetric Kitaev model, linking it to fermionic magnon correlations and experimental spectroscopic signatures.

Findings

Spin dynamics equals density-density correlation of fermionic magnons.

Characteristic momentum dependence in RIXS related to fermionic dispersion.

Neutron scattering shows mixed fermionic magnon and spin-orbital responses.

Abstract

We provide an exact study of dynamical correlations for the quantum spin-orbital liquid phases of an SU(2)-symmetric Kitaev honeycomb lattice model. We show that the spin dynamics in this Kugel-Khomskii type model is exactly the density-density correlation function of S=1 fermionic magnons, which could be probed in resonant inelastic x-ray scattering experiments. We predict the characteristic signatures of spin-orbital fractionalization in inelastic scattering experiments and compare them to the ones of the spin-anisotropic Kitaev honeycomb spin liquid. In particular, the resonant inelastic x-ray scattering response shows a characteristic momentum dependence directly related to the dispersion of fermionic excitations. The neutron scattering cross section displays a mixed response of fermionic magnons as well as spin-orbital excitations. The latter has a bandwidth of broad excitations and a vison gap that is three times larger than that of the spin-1/2 Kitaev model.