We investigate the lattice dynamics in the spin-1/2 frustrated kagome compound herbertsmithite ZnCu3(OH)6Cl2 by a combination of infrared spectroscopy measurements and ab initio density functional theory calculations, and provide an unambiguous assignment of infrared-active lattice vibrations involving in-plane and out-of-plane atom displacements in the kagome layers. Upon cooling, non-thermal red-shifts and broadening appear specifically for modes that deform the kagome layer or affect the Cu-O-Cu bond angles, thus creating pronounced modifications of the antiferromagnetic exchange coupling. Our results indicate the presence of a strong magnetoelastic coupling to the spin system. We discuss the effects of this coupling and its relation to recent experiments reporting a global symmetry reduction of the kagome lattice symmetry.
@article{arxiv.2002.04042,
title = {Lattice dynamics in the spin-1/2 frustrated kagome compound herbertsmithite},
author = {Ying Li and A. Pustogow and M. Bories and P. Puphal and C. Krellner and M. Dressel and Roser Valenti},
journal= {arXiv preprint arXiv:2002.04042},
year = {2020}
}