抄録
The critical dynamical behavior of the pseudospin-phonon coupled system has been investigated in connection with the structural phase transition of molecular crystals. Based on Onsager’s equation of motion, explicit expressions for three correlation functions, spin-spin correlation, phonon-phonon correlation and spin-phonon correlation, are obtained. It has been shown that the characteristic of the spectra of these correlation functions shows wide variation depending on the values of two parameters: The ratio of the relaxation rate of reorientational motion of an isolated spin and the frequency of the phonon, and the ratio of the interaction parameter of direct spin-spin coupling and that of spin-phonon coupling. Especially, in ‘fast relaxation case’, the spectrum of phonon-phonon correlation shows critical softening, whereas, in ‘slow relaxation case’ the spectrum gives ‘triple peak’ structure and only the central (relaxational) mode shows critical slowing down leaving phonon side peaks unchanged.
