Aerogel Growth, Optical Birefringence Characterization, and Use in Ultra Low Temperature Superfluid

Superfluid He has important implications in studying condensed matter physics, specifically in its phases at very low temperatures. The understanding of these phases not only expands our knowledge of He itself, but is also a paradigm for recently discovered unconventional superconductors such as strontium ruthenate (SrRuO3) and uranium platinum three (UPt3). Superfluid He’s relation to superconductors is not in its pure form, but in dirty superfluid He, where impurities from external sources are present. This is because real superconductors, unlike ideal ones, contain unavoidable impurities. In He, however, we can control the number of impurities and how they are distributed in space. These impurities are introduced by filling the extremely porous structure of silica aerogel with He. The aerogel pore size is on a scale that causes He particles to scatter, similar to the behavior brought about by impurities in other unconventional systems. The microstructure of the aerogel plays an integral role in the modification of the He system. Presented here are aerogel growth methods developed to control this microstructure, and the employment of optical birefringence as an aerogel characterization technique. Introduction and Motivation