Observation of the Smectic C -- Smectic I Critical Point

TL;DR

This paper reports the first experimental observation of the critical point between smectic C and smectic I phases in a binary system, supporting recent theories on universality classes in layered liquid crystal phases.

Contribution

First experimental detection of the smectic C--smectic I critical point, confirming theoretical predictions about phase symmetry and universality classes in layered liquid crystal systems.

Findings

Observation of the C--I critical point via X-ray diffraction.

Evidence supporting the theory of a new universality class for layered systems.

Confirmation that coupling to molecular tilt induces hexatic order in the C phase.

Abstract

We report the first observation of the smectic C--smectic I (C--I) critical point by Xray diffraction studies on a binary system. This is in confirmity 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.