Anisotropic Aerogels for Studying Superfluid $^3$He

TL;DR

This paper explores methods to induce anisotropy in silica aerogels to potentially stabilize new superfluid phases of helium-3, using uniaxial strain and growth-induced anisotropy, with experimental validation via SAXS.

Contribution

It introduces two novel methods to create anisotropic aerogels and investigates their effects on superfluid helium-3 stabilization.

Findings

Anisotropy can be controlled via uniaxial strain and growth processes.

Growth-induced anisotropy is approximately 90° out of phase with strain-induced anisotropy.

Correlations between anisotropy and superfluid phase stabilization are discussed.

Abstract

It may be possible to stabilize new superfluid phases of $^{3}$He with anisotropic silica aerogels. We discuss two methods that introduce anisotropy in the aerogel on length scales relevant to superfluid $^{3}$He. First, anisotropy can be induced with uniaxial strain. A second method generates anisotropy during the growth and drying stages. We have grown cylindrical $\sim$98% aerogels with anisotropy indicated by preferential radial shrinkage after supercritical drying and find that this shrinkage correlates with small angle x-ray scattering (SAXS). The growth-induced anisotropy was found to be $\sim90^\circ$ out of phase relative to that induced by strain. This has implications for the possible stabilization of superfluid phases with specific symmetry.