Divergent thermal diffusivity at a mean-field tricritical point

A sharp divergence is observed in the thermal diffusivity very close to the transition temperature of a smectic-A--smectic-C transition that is known to be at a mean-field tricritical point. Similar but less pronounced behavior near other smectic-A--smectic-C transitions reveals a relationship between the size of this anomaly and the proximity of the system to a tricritical point. An application of the Ginzburg criterion suggests that this novel behavior might indicate a crossover to an asymptotic critical regime.