NEUTRON-SCATTERING OBSERVATION OF SOLITONS

It has been suggested that in systems with strong fluctuations as around a critical point strongly nonlinear effects should occur. The simplest possible equation for nonlinear dynamics is the sine-Gordon equation. This equation can be applied to the dynamics of a 1-D-ferromagnetic chain with planar anisotropy in a symmetry-breaking field (magnetic field perpendicular to the chain direction). The dynamics of such a system consist of two types of elementary excitations: nonlinear modes (solitons and breathers) and linear modes (spin waves). The thermodynamics for the nonlinear modes are the same as for a gas of noninteracting relativistic quasi-particles. In the frame of that picture the dynamic structure factor for an inelastic neutron scattering experiment can be calculated for the relativistic case, and it appears that inelastic n-scattering is the most direct way for the observation of solitons. Experimental results, obtained for CsNiF3 are discussed and compared with the theoretical results. These experimental results show that nonlinear modes are indeed an essential part of the dynamics of that system.