Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling

TL;DR

This study investigates how magnon-phonon coupling affects spin excitations in hexagonal HoMnO3, revealing that phonons primarily cause the observed magnon energy renormalization, with magnon-magnon interactions playing a lesser role.

Contribution

It provides a quantitative analysis demonstrating that magnon-phonon coupling is the main cause of magnon energy renormalization in HoMnO3, using advanced modeling techniques.

Findings

Magnon energies are renormalized around 11 meV.

Magnon-phonon coupling is the primary cause of renormalization.

Magnon-magnon interactions are suppressed by anisotropy.

Abstract

Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been studied via inelastic neutron scattering. A simple Heisenberg model with a single-ion anisotropy describes most features of the spin-wave dispersion curves. However, there is shown to be a renormalization of the magnon energies located at around 11 meV. Since both the magnon-magnon interaction and magnon-phonon coupling can affect the renormalization in a noncollinear magnet, we have accounted for both of these couplings by using a Heisenberg XXZ model with 1=S expansions [1] and the Einstein site phonon model [13], respectively. This quantitative analysis leads to the conclusion that the renormalization effect primarily originates from the magnon-phonon coupling, while the spontaneous magnon decay due to the magnon-magnon interaction is suppressed by strong two-ion anisotropy.