title: ESR investigation on the breather mode and the spinon-breather dynamical crossover in Cu benzoate.
abstract: A "breather excitation" is observed directly by electron spin resonance in the quantum spin chain Cu benzoate, in which an unexpected field-induced gap has recently been found. The nonlinear field dependence of the resonance field agrees well with the formula based on a quantum sine-Gordon model. The power-law temperature dependence of the linewidth is observed in the gapless spinon regime while the width decreases exponentially for the gapped breather regime. In the intermediate range, a distinct anomaly is found, which is the manifestation of "the spinon-breather dynamical crossover."
authors.affiliation: Department of Physics, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Asano
authors.forename: H
authors.initials: H
authors.lastname: Nojiri
authors.forename: Y
authors.initials: Y
authors.lastname: Inagaki
authors.forename: J P
authors.initials: JP
authors.lastname: Boucher
authors.forename: T
authors.initials: T
authors.lastname: Sakon
authors.forename: Y
authors.initials: Y
authors.lastname: Ajiro
authors.forename: M
authors.initials: M
authors.lastname: Motokawa