The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of great debate. We conducted 17-O single crystal NMR measurements of the S=1/2 kagome lattice in herbertsmithite ZnCu3(OH)6Cl2, which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrate that the intrinsic local spin susceptibility χkagome deduced from the 17-O NMR frequency shift asymptotes to zero below temperature T ~ 0.03 J, where J ~ 200 K is the Cu-Cu super-exchange interaction. Combined with the magnetic field dependence of χkagome we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.
@article{arxiv.1511.02174,
title = {Evidence for a Gapped Spin-Liquid Ground State in a Kagome Heisenberg Antiferromagnet},
author = {M. Fu and T. Imai and T. -H. Han and Y. S. Lee},
journal= {arXiv preprint arXiv:1511.02174},
year = {2015}
}