Correlated impurities and intrinsic spin liquid physics in the kagome material Herbertsmithite

TL;DR

This study uses neutron scattering to differentiate impurity and intrinsic spin dynamics in Herbertsmithite, revealing impurity correlations, a small spin gap, and providing insights into the intrinsic spin liquid behavior.

Contribution

It introduces a method to distinguish impurity effects from intrinsic kagome spin liquid physics using neutron scattering data.

Findings

Impurity spins show antiferromagnetic correlations at low energies.

Evidence of a small spin gap (~0.7 meV) in kagome layers.

Impurity lattice resembles a simple cubic structure in dilute limit.

Abstract

Low energy inelastic neutron scattering on single crystals of the kagome spin liquid compound ZnCu3(OD)6Cl2 (Herbertsmithite) reveals antiferromagnetic correlations between impurity spins for energy transfers E < 0.8 meV (~J/20). The momentum dependence differs significantly from higher energy scattering which arises from the intrinsic kagome spins. The low energy fluctuations are characterized by diffuse scattering near wavevectors (1 0 0) and (0 0 3/2), which is consistent with antiferromagnetic correlations between pairs of nearest neighbor Cu impurities on adjacent triangular (Zn) interlayers. The corresponding impurity lattice resembles a simple cubic lattice in the dilute limit below the percolation threshold. Such an impurity model can describe prior neutron, NMR, and specific heat data. The low energy neutron data are consistent with the presence of a small spin-gap (Delta ~ 0.7 meV) in the kagome layers, similar to that recently observed by NMR. The ability to distinguish the scattering due to Cu impurities from that of the planar kagome Cu spins provides a new avenue for probing intrinsic spin liquid physics.