External-Field-Induced Tricritical Point in a Fluctuation-Driven Nematic–Smectic-ATransition

Abstract

We study theoretically the effect of an external field on the nematic–smectic-A transition close to the tricritical point, where fluctuation effects govern the qualitative behavior of the transition. An external field suppresses nematic-director fluctuations by making them massive. For a fluctuation-driven firstorder transition, we show that an external field can drive the transition second order. In an appropriate liquid-crystal system, we predict the required magnetic field to be of order 10 T. The equivalent electric field is of order 1 V�mm.