Polarization and tilt-angle measurements near the smectic-A–chiral–smectic-Ctransition ofp-(n-decyloxybenzylidene)-p-amino-(2-methyl-butyl)cinnamate (DOBAMBC)

For a given temperature below the smectic-A (SmA)–chiral–smectic-C (${\mathrm{SmC}}^{\mathrm{*}}$) transition of DOBAMBC, polarization (P) and tilt-angle (theta) have been measured almost simultaneously with high resolution. The ratio P/theta stays fairly constant for ${\mathrm{T}}_{\mathrm{c}}$-T>2 K and shows a precipitous drop near the transition temperature (${\mathrm{T}}_{\mathrm{c}}$). A calculation based on a generalized mean-field model, similar to the one proposed by Zeks, is in good agreement with our result. This generalized mean-field model also gives the prominent feature of the helical pitch anomaly just below the SmA-${\mathrm{SmC}}^{\mathrm{*}}$ transition.