title: Dominance of the excitation continuum in the longitudinal spectrum of weakly coupled Heisenberg S=1/2 chains.
abstract: A low-field spin-flop transition in the quasi-one-dimensional antiferromagnet BaCu2Si2O7 is exploited to study the polarization dependence of low-energy magnetic excitations. The measured longitudinal spectrum is best described as a single broad continuum, with no sharp "longitudinal mode," in apparent contradiction with the commonly used chain-mean-field and random phase approximation (MF/RPA) theories. The observed behavior is also quite different than that previously seen in the related KCuF3 material, presumably due to a large difference in the relative strength of interchain interactions. The results highlight the limitations of the chain-MF/RPA approach.
authors.affiliation: Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA. zheludevai@ornl.gov
authors.forename: A
authors.initials: A
authors.lastname: Zheludev
authors.forename: K
authors.initials: K
authors.lastname: Kakurai
authors.forename: T
authors.initials: T
authors.lastname: Masuda
authors.forename: K
authors.initials: K
authors.lastname: Uchinokura
authors.forename: K
authors.initials: K
authors.lastname: Nakajima