Optical phonons coupled to a Kitaev spin liquid
Alexandros Metavitsiadis, W. M. H. Natori, Johannes Knolle, Wilhelm Brenig
Abstract
Emergent excitation continua in frustrated magnets are a fingerprint of fractionalization, characteristic of quantum spin-liquid states. Recent evidence from Raman scattering for a coupling between such continua and lattice degrees of freedom in putative Kitaev magnets may provide insight into the nature of the fractionalized quasiparticles. Here we study the renormalization of optical phonons coupled to the underlying ${\mathbb{Z}}_{2}$ quantum spin liquid. We show that phonon line shapes acquire an asymmetry, observable in light scattering and originating from two distinct sources, namely, the dispersion of the Majorana continuum and the Fano effect. Moreover, we find that the phonon lifetimes increase with increasing temperature due to thermal blocking of the available phase space. Finally, in contrast to low-energy probes, optical phonon renormalization is rather insensitive to thermally excited gauge fluxes and barely susceptible to external magnetic fields.