Theory of Central Peak in Quasi-One-Dimensional Ferroelectric systems —Application to CsD₂PO₄—

Linear response of weakly coupled ϕ⁴ chains is investigated. The transfer integral method can be applied when the effect of the interchain coupling is taken into account using the mean field approximation. The Fokker-Planck equation is solved with a simple decoupling approximation for the phase space distribution function. We find a central peak structure in the dynamical structure factor. The intensity of the central peak diverges at the ferroelectric transition. This corresponds to the “softening” of the response of the domain wall. These phenomena may be observed in quasi-one-dimensional system such as CsD₂PO₄.