Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet

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Science  06 Nov 2015:
Vol. 350, Issue 6261, pp. 655-658
DOI: 10.1126/science.aab2120

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Peeking into an exotic magnetic structure

Cooling materials that contain magnetic interactions generally leads to an ordered magnetic state. In materials known as quantum spin liquids (QSLs), the geometry of the crystal lattice may prevent this ordered state from forming, even at absolute zero. The material herbertsmithite is thought to be a strong candidate for a QSL, but the nature of its ground state is still a mystery. Fu et al. measured shifts in the nuclear magnetic resonance signals of herbertsmithite to conclude that its ground state has a zero spin and is separated from the first excited state by an energy gap (see the Perspective by Furukawa). The results suggest that herbertsmithite is indeed a QSL.

Science, this issue p. 655; see also p. 631


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 active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

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