title: Continuum in the spin-excitation spectrum of a haldane chain observed by neutron scattering in CsNiCl3.
abstract: The spin-excitation continuum, expected to dominate the low-energy fluctuation spectrum in the Haldane spin chain around the Brillouin zone center, q = 0, is directly observed by inelastic magnetic neutron scattering in the S = 1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode approximation fails, and that a finite energy width appears in the dynamic correlation function S(q,omega) for q less, similar 0.5 pi. The width increases with decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively similar to that predicted for the two-magnon continuum in the nonlinear sigma-model.
authors.affiliation: Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
authors.forename: I A
authors.initials: IA
authors.lastname: Zaliznyak
authors.forename: S H
authors.initials: SH
authors.lastname: Lee
authors.forename: S V
authors.initials: SV
authors.lastname: Petrov