Observation of the Smectic-C—Smectic-I Critical Point

Abstract

We report the first observation of the smectic-C—smectic-I (C-I) critical point by x-ray diffraction studies on a binary system. These results are in agreement with the theoretical idea of Nelson and Halperin that coupling to the molecular tilt should induce hexatic order even in the C phase, and as such both C and I (a tilted hexatic phase) should have the same symmetry. The results provide evidence in support of the recent theory of Defontaines and Prost proposing a new universality class for critical points in layered systems.