On the low-frequency dynamics of the classical sine-Gordon chain

The authors discuss the low-frequency response of the classical sine-Gordon chain with respect to the lowest-order corrections to the non-interacting soliton/magnon picture. They show that the strength of the soliton-induced central peak is considerably reduced by the interference with magnons. In addition, an appreciable contribution to the central peak is obtained from terms analytic in temperature, which may be attributed to breathers or to anharmonic magnon processes. Quantitative estimates of the results are given and compared to experimental results on CsNiF 3 in an external magnetic field.