Site Specific X-ray Anomalous Dispersion of the Geometrically Frustrated Kagomé Magnet, Herbertsmithite, ZnCu₃(OH)₆Cl₂

TLDR

This geometrically frustrated kagomé antiferromagnet is a leading candidate for a spin‑liquid ground state, yet chemical disorder has been proposed as a mundane explanation for its magnetic properties. We apply a site‑specific X‑ray anomalous dispersion technique to investigate Zn–Cu chemical disorder in ZnCu₃(OH)₆Cl₂. Structural characterization exploiting X‑ray scattering differences at elemental absorption edges is developed to quantitatively determine crystallographic site‑specific metal disorder. Using anomalous scattering at the Zn and Cu edges, we find no Zn occupation of the intralayer Cu sites within the kagomé layer, but Cu is present on the Zn intersite, yielding a structural formula of (Zn₀.₈₅Cu₀.₁₅)Cu₃(OH)₆Cl₂, and this lack of Zn mixing onto the kagomé lattice supports a nontrivial electronic ground state.

Abstract

Structural characterization, exploiting X-ray scattering differences at elemental absorption edges, is developed to quantitatively determine crystallographic site-specific metal disorder. We apply this technique to the problem of Zn−Cu chemical disorder in ZnCu3(OH)6Cl2. This geometrically frustrated kagomé antiferromagnet is one of the best candidates for a spin-liquid ground state, but chemical disorder has been suggested as a mundane explanation for its magnetic properties. Using anomalous scattering at the Zn and Cu edges, we determine that there is no Zn occupation of the intralayer Cu sites within the kagomé layer; however there is Cu present on the Zn intersite, leading to a structural formula of (Zn0.85Cu0.15)Cu3(OH)6Cl2. The lack of Zn mixing onto the kagomé lattice sites lends support to the idea that the electronic ground state in ZnCu3(OH)6Cl2 and its relatives is nontrivial.