Observation of solitons as a gas of quasiparticles in CsNiF3

Abstract

An inelastic neutron scattering study of CsNiF3 in an external magnetic field at q6=0.1 r.1.u. revealed a central component in the energy spectrum besides the spinwave resonances. The temperature and field dependency of the intensity and the width of the central component could be well explained by the following picture: A 1-dimensional ferromagnet with planar anisotropy like CsNiF3 can be described by a sine-Gordon-Hamiltonian if a field is applied in the easy plane. The nonlinear excitations of this Hamiltonian appear in the neutron scattering experiment as a gas of thermally excited quasiparticles. The agreement between theory and experiment leads to the conclusion that the central component is due to scattering from thermally activated solitons.