title: Scale-free antiferromagnetic fluctuations in the s = 1/2 kagome antiferromagnet herbertsmithite.
abstract: Neutron spectroscopy and diffuse neutron scattering on herbertsmithite [ZnCu(3)(OH)(6)Cl(2)], a near-ideal realization 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 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 favor of resonating-valence-bond theories of (doped) Mott insulators.
authors.affiliation: School of Physics & Astronomy, University of St-Andrews, the North Haugh, St Andrews, KY16 9SS, United Kingdom. m.a.devries@physics.org
authors.forename: M A
authors.initials: MA
authors.lastname: de Vries
authors.forename: J R
authors.initials: JR
authors.lastname: Stewart
authors.forename: P P
authors.initials: PP
authors.lastname: Deen
authors.forename: J O
authors.initials: JO
authors.lastname: Piatek
authors.forename: G J
authors.initials: GJ
authors.lastname: Nilsen
authors.forename: H M
authors.initials: HM
authors.lastname: Rønnow
authors.forename: A
authors.initials: A
authors.lastname: Harrison