Disordering to Order: de Vries behavior from a Landau theory for smectics

TL;DR

This paper uses Landau theory to explain de Vries behavior in smectic phases, showing it can occur under certain conditions with minimal layer contraction and specific birefringence patterns, aligning with experimental observations.

Contribution

It demonstrates that Landau theory can account for de Vries behavior in smectics, highlighting conditions like small orientational order and first-order transitions.

Findings

De Vries behavior can occur with little layer contraction.

Birefringence decreases then increases across the transition.

First-order transitions can also exhibit de Vries characteristics.

Abstract

We show that Landau theory for the isotropic, nematic, smectic A, and smectic C phases generically, but not ubiquitously, implies de Vries behavior. I.e., a continuous AC transition can occur with little layer contraction; the birefringence decreases as temperature T is lowered above this transition, and increases again below the transition. This de Vries behavior occurs in models with unusually small orientational order, and is preceded by a first order I − A transition. A first order AC transition with elements of de Vries behavior can also occur. These results correspond well with experimental work to date.