High Porosity Silica Aerogels Engineered for Superfluid $^{3}$He Research

Silica aerogel is a network of strands with a diameter of 3 nm and average separation \textit{$\xi $}$_{a}\approx $ 30 -- 100 nm. Low-density aerogel can be used to introduce disorder in superfluid $^{3}$He because the superfluid coherence length is of the same order as \textit{$\xi $}$_{a}$. We have developed novel sample growth and preparation techniques for producing aerogels for a variety of measurements on superfluid $^{3}$He. In particular, it has been proposed that anisotropic aerogels can be used to understand the stability of the A-like superfluid $^{3}$He phases [1, 2]. We can introduce anisotropy in aerogel on length scales relevant to superfluid $^{3}$He. Anisotropy can be induced with uniaxial strain, or alternatively, during growth and drying stages. We have performed small angle x-ray scattering to probe these two types of anisotropy and find that uniaxial strain can be used to tune between them. [1] C.L. Vicente, \textit{et al.}, \textit{Phys. Rev. B.} \textbf{72}, 094519 (2005). [2] K. Aoyama and R. Ikeda, \textit{Phys. Rev. B} \textbf{73}, 060504(R) (2006).