2-SOLITON EXCITATIONS AND SPIN-WAVE RESPONSES IN THE ANTIFERROMAGNETS CSCOBR3 AND CSCOCL3

An Ising-like S = 1/2 antiferromagnet with a weak next-nearest-neighbor interaction J' on a chain is considered to explain the spin-wave responses in CsCoBr3 and CsCoCl3 at the paramagnetic regime. Two-soliton excitations are investigated by use of both a perturbation method and a numerical method of finite systems. In addition to extended two-soliton states, a bound state of two solitons is obtained. At T = 0, when J' is ferromagnetic (J' > 0), the dynamical structure factor S(xx)(q,omega) exhibits a sharp peak at a lower energy and a tail at higher energies, while the peak occurs at a higher energy for J' < 0. The dispersion of the peak energy is almost symmetric about the zone boundary. At T not-equal-to 0, due to an interaction between solutions, the peak broadens and the dispersion becomes asymmetric. The results for J' > 0 are compared with the experimental observations of S(xx)(q,omega) made by Nagler et al. An excellent agreement is obtained over the whole Brillouin zone at different temperatures. The values of J' are estimated J'/J approximately 0.1 for the first time in those substances, where J is the nearest-neighbor interaction.