Nematic--to--Smectic-A Transition in Aerogel

TL;DR

This paper models the Nematic--Smectic-A transition in aerogel, showing that even weak disorder destroys smectic and nematic order, eliminating the sharp transition and preventing a Bragg glass phase, aligning with experimental observations.

Contribution

It introduces a model accounting for quenched disorder effects on the NA transition, predicting the absence of a Bragg glass phase and the destruction of order.

Findings

Disorder destroys smectic and nematic order.

No Bragg glass phase exists in this system.

The NA transition becomes thermodynamically broad and is destroyed.

Abstract

We study a model for the Nematic--Smectic-A (NA) transition in aerogel, and find that even arbitrarily weak quenched disorder (i.e., low aerogel density) destroys translational (smectic) order. Ignoring elastic anharmonicities, but keeping anharmonic couplings to disorder, leads to the prediction that there is no ``Bragg glass'' phase in this system: it is riddled with dislocation loops induced by the quenched disorder. Orientational (nematic) order is destroyed as well, as is the thermodynamically sharp NA transition, in agreement with recent experimental results.