External-field-induced tricritical point in a fluctuation-driven nematic-smectic-A transition

TL;DR

This paper theoretically investigates how an external magnetic or electric field can change the nematic-smectic-A transition from first-order to second-order near a tricritical point by suppressing fluctuations, with predictions for field strengths needed.

Contribution

It demonstrates that external fields can induce a change from first-order to second-order transition in fluctuation-driven systems near a tricritical point.

Findings

External magnetic field of about 10 T can induce the transition change.

Electric field of about 1 V/μm can have a similar effect.

Fluctuation effects are suppressed by external fields, altering transition order.

Abstract

We study theoretically the effect of an external field on the nematic-smectic-A (NA) 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 first-order 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 $1 V/\mu m$.