title: Order by distortion and string modes in pyrochlore antiferromagnets.
abstract: We study the effects of magnetoelastic couplings on pyrochlore antiferromagnets. We employ Landau theory, extending an investigation begun by Yamashita and Ueda for the case of S = 1, and classical analyses to argue that such couplings generate bond order via a spin-Peierls transition. This is followed by, or concurrent with, a transition into one of several possible low-temperature Néel phases, with most simply collinear, but also coplanar or mixed spin patterns. In a collinear Néel phase, a dispersionless stringlike magnon mode dominates the resulting excitation spectrum, providing a distinctive signature of the parent geometrically frustrated state. We comment on the experimental situation.
authors.affiliation: School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA.
authors.forename: Oleg
authors.initials: O
authors.lastname: Tchernyshyov
authors.forename: R
authors.initials: R
authors.lastname: Moessner
authors.forename: S L
authors.initials: SL
authors.lastname: Sondhi