Scale-free antiferromagnetic fluctuations in the S=1/2 kagome antiferromagnet herbertsmithite

TL;DR

This study uses neutron scattering to reveal persistent, scale-free antiferromagnetic fluctuations in herbertsmithite, supporting the quantum spin liquid state and RVB theories in kagome antiferromagnets.

Contribution

It provides experimental evidence of gapless spinons and scale-free fluctuations in herbertsmithite, a near-ideal S=1/2 kagome antiferromagnet, supporting RVB theories.

Findings

Persistent antiferromagnetic correlations up to 25 meV and 120 K.

Observation of low-Q shift indicating gapless spinons.

Weak dependence of correlations on energy transfer and temperature.

Abstract

Neutron spectroscopy and diffuse neutron scattering on herbertsmithite [ZnCu3 (OH)6Cl2], a near-ideal realisation of the s = 1/2 kagome antiferromagnet, reveal the hallmark property of a quantum spin liquid; instantaneous short-ranged antiferromagnetic correlations in the absence of a time-averaged ordered moment. These dynamic antiferromagnetic correlations are only very weakly dependent of neutron-energy transfer and temperature, and persist up to 25 meV and 120 K. At low energy transfers a shift of the magnetic scattering to low Q is observed with increasing temperature, providing evidence of gapless spinons. It is argued that these observations provide important evidence in favour of RVB theories of (doped) Mott insulators.