Quasielastic Rayleigh Scattering in a Smectic-ACrystal

Abstract

Using a light-beating spectrometer, we have observed in the smectic-$A$ phase of $p$-cyanobenzilidene-$p$-octyloxyaniline the thermally excited undulations of layers predicted by de Gennes. From the wave-vector dependence of their damping time we determined the diffusivity of the angular orientation, $\frac{K_1}{\eta }=(2.0\mathrm{}\pm 0.2)\times {10}^{-6\mathrm{}}$ cgs. From the thickness dependence of the boundary quenching, we determined the penetration length, $\lambda =14\mathrm{}\pm 1$ Å at 75°C.