Lattice dynamics in the spin-1/2 frustrated Cu-based kagome compounds*

The nature of the ground state in the frustrated spin-1/2 Cu-based kagome compounds such as herbertsmithite ZnCu₃(OH)₆Cl₂ has been the subject of intense discussion for many years. The knowledge on the nature of the vibrational modes in this system and the magnetoelastic coupling would be of major help to resolve the magnetic ground states of these materials. We investigate the lattice dynamics in herbertsmithite ZnCu₃(OH)₆Cl₂ and a newly synthesized Cu-based Kagome compound Y₃Cu₉(OH)₁₉Cl₈ [1] by a combination of infrared spectroscopy measurements and ab initio density functional theory calculations. The results provide an unambiguous assignment of infrared-active lattice vibrations involving in-plane and out-of-plane atom displacements in the kagome layers and indicate the presence of a strong magnetoelastic coupling to the spin system [2]. We further discuss similarities and differences between ZnCu₃(OH)₆Cl₂ and Y₃Cu₉(OH)₁₉Cl₈.
[1] P. Puphal, M. Bolte, D. Sheptyakov, et al., J. Mater. Chem. C, 5, 2629 (2017).
[2] Y. Li, A. Pustogow, M. Bories, et al., Phys. Rev. B 101, 161115 (R) (2020).