Dynamic correlations below the anti-ferrodistortive transition in perovskites

Abstract

Dynamic behavior in certain perovskites below the anti-ferrodistortive transition is studied along the longitudinal excitation branch by investigating effects of weak anisotropy for a n = 3 component order parameter field. Exploiting the consequences of small deviations from isotropy and of the relatively high frequencies involved, it is found that the longitudinal excitation frequency ω_L may be expected to be proportional to the average value P of the order parameter beyond the static mean-field region of temperatures. Experimental implications of our theory are briefly discussed.