Field-induced decays in $XXZ$ triangular-lattice antiferromagnets

TL;DR

This paper studies how magnetic fields cause magnon decay phenomena in the $XXZ$ model on a triangular lattice, predicting observable spectrum modifications in the material Ba$_3$CoSb$_2$O$_9$ due to anharmonic magnon interactions.

Contribution

It provides concrete theoretical predictions for field-induced magnon decay effects in the $XXZ$ model, especially in the context of the real material Ba$_3$CoSb$_2$O$_9$, highlighting the impact of anisotropy and magnetic field strength.

Findings

Magnon spectrum undergoes dramatic changes in low out-of-plane fields.

Coexistence of well-defined and broadened magnon excitations in different ${f k}- ext{space}$ regions.

Field-induced decays become more prominent with increased anisotropy and higher magnetic fields.

Abstract

We investigate field-induced transformations in the dynamical response of the $XXZ$ model on the triangular lattice that are associated with the anharmonic magnon coupling and decay phenomena. A set of concrete theoretical predictions is made for a close physical realization of the spin-1/2 $XXZ$ model, Ba$_3$CoSb$_2$O$_9$. We demonstrate that dramatic modifications in magnon spectrum must occur in low out-of-plane fields that are easily achievable for this material. The hallmark of the effect is a coexistence of the clearly distinct well-defined magnon excitations with significantly broadened ones in different regions of the ${\bf k}-\omega$ space. The field-induced decays are generic for this class of models and become more prominent at larger anisotropies and in higher fields.