Evidence of a first-order smectic -- hexatic transition and its proximity to tricritical point in smectic films

TL;DR

This study provides experimental and theoretical evidence of a first-order smectic-hexatic phase transition in thin films, showing how the transition's nature and coexistence region depend on film thickness and proximity to a tricritical point.

Contribution

It demonstrates the first-order nature of the smectic-hexatic transition and models the coexistence width dependence on film thickness near the tricritical point using Landau theory.

Findings

Discontinuous first-order transition into the hexatic phase.

Coexistence region diminishes with decreasing film thickness.

Surface hexatic order penetrates deeply near the tricritical point.

Abstract

Experimental and theoretical studies of a smectic-hexatic transition in freely suspended films of 54COOBC compound are presented. X-ray investigations revealed a discontinuous first-order transition into the hexatic phase. Moreover, the temperature region of two phase coexistence near the phase transition point diminishes with film thickness. The coexistence width dependence on film thickness was derived on the basis of the Landau mean-field theory in the vicinity of the tricritical point (TCP). Close to TCP the surface hexatic ordering penetrates anomalously deep into the film interior.