X-Ray Study of Fluctuations near the Nematic-Smectic-A-Smectic-CMulticritical Point

We present the results of a high-resolution x-ray-scattering study of the pretransitional fluctuations above the nematic-to-smectic-$C$ phase boundary in the ¯7S5/8OCB system. The fluctuations are well described by the Lifshitz-point model of Chen and Lubensky with minimal adjustable parameters. We have located the line along which the x-ray cross section $\sigma \left(\mathrm{q}\right)$ exhibits pure $q_{\perp }^{-4\mathrm{}}$ fluctuations. Close to the nematic-smectic-$A$-smectic-$C$ point this line is simply related to the smectic-$A$-smectic-$C$ transition boundary.