TO CRITICAL-DYNAMICS NEAR STRUCTURAL PHASE-TRANSITIONS IN FERROELECTRICS - CENTRAL-MODE AND SOFT-MODE BEHAVIOR

We analyze the critical dynamics of the order-disorder phase transitio n through the pseudo-spin quantum and classical Ising models. The find ings derived by the Green-function equation-motion method and realized through Tyablikov's and Tserkovnikov's schemes, on the one hand, and the Thompson-Silva renormalization group approach, on the other hand a re discussed. The slowing-down Delta and the dynamical z critical expo nents are predicted for the relaxation (Delta = 5/4, z = 2) and resona nt (Delta = 5/16, z = 1/2) motion regimes for three-dimensional Ising models. The results obtained give support to the idea that the classic al and quantum d = 2,3 Ising models at nonzero critical temperature be long to the same universality class.