Critical Slowing Down of Biaxiality Fluctuations at the Uniaxial-to-Biaxial Phase Transition in a Lyotropic Disklike Nematic Liquid Crystal

Using a light-beating, Rayleigh-scattering technique, we observe the thermally excited biaxiality fluctuations which appear in the uniaxial disklike phase of a potassium-laurate, 1-decanol, ${\mathrm{D}}_2$O mixture close to the biaxial phase. The two polarized- and depolarized-mode linewidths undergo a critical slowing down, in agreement with a Landau-type prediction. From the wave-vector dependence of the damping rate, one estimates the bare transverse correlation length to be comparable with 2 micelle diameters.