title: First-order transition in the spin dynamics of geometrically frustrated Yb2Ti2O7.
abstract: Using neutron diffraction, 170Yb Mössbauer and muon spin relaxation spectroscopies, we have examined the pyrochlore Yb2Ti2O7, where the Yb3+S' = 1/2 ground state has planar anisotropy. Below approximately 0.24 K, the temperature of the known specific-heat lambda transition, there is no long range magnetic order. We show that the transition corresponds to a first-order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate, in the GHz range, follows a thermal excitation law, whereas below, the rate, in the MHz range, is temperature independent, indicative of a quantum fluctuation regime.
authors.affiliation: CEA-Saclay, DRECAM-SPEC, 91191 Gif-sur-Yvette, France.
authors.forename: J A
authors.initials: JA
authors.lastname: Hodges
authors.forename: P
authors.initials: P
authors.lastname: Bonville
authors.forename: A
authors.initials: A
authors.lastname: Forget
authors.forename: A
authors.initials: A
authors.lastname: Yaouanc
authors.forename: P
authors.initials: P
authors.lastname: Dalmas de Réotier
authors.forename: G
authors.initials: G
authors.lastname: André
authors.forename: M
authors.initials: M
authors.lastname: Rams
authors.forename: K
authors.initials: K
authors.lastname: Królas
authors.forename: C
authors.initials: C
authors.lastname: Ritter
authors.forename: P C M
authors.initials: PC
authors.lastname: Gubbens
authors.forename: C T
authors.initials: CT
authors.lastname: Kaiser
authors.forename: P J C
authors.initials: PJ
authors.lastname: King
authors.forename: C
authors.initials: C
authors.lastname: Baines