Multiparticle States in theS=1Chain SystemCsNiCl3

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound ${\mathrm{CsNiCl}}_3$ in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point $Q_c=\pi$, the continuum lies higher in energy than the Haldane gapped excitations. At $6\mathrm{K}$ the integrated intensity of the continuum is about $12\left(2\right)\%$ of the total spectral weight. This result is considerably larger than the $1\%–3\%$ weight predicted by the nonlinear sigma model for the three-particle continuum.