CHARACTERIZING THE NATURE OF THE SMECTIC-A-SMECTIC-C AND SMECTIC-A-SMECTIC-C-ASTERISK TRANSITIONS

We provide a theoretical explanation of the critical (i.e. non-mean-fi eld) behavior of specific heat at the SmA-SmC transition, as it has re cently been observed on certain compounds. This explanation rests on t he Andereck and Swift free energy introducing terms which couple the o rder-parameter with both layer-compression and density. We show that t he behavior of specific-heat depends on the intensity of these couplin gs, and that the behaviors which can be observed are therefore of the mean-field, Gaussian or 3DXY type.