Critical Angular Fluctuations of Molecules above a Second-Order Smectic-Ato Smectic-CPhase Transition

Abstract

Using light-beating spectroscopy we detect the "soft" mode associated with the secondorder smectic-$A$ to smectic-$C$ phase transition in undecylazoxymethylcinnamate. This mode corresponds to angular fluctuations of molecules with respect to the normal of the layers. In the $A$ phase both the amplitude and the relaxation time of these fluctuations diverge with a mean-field critical exponent $\gamma =1.0+0.15\mathrm{}$.