Evidence for a disorder induced phase transition in the condensation of 4He in aerogels

TL;DR

This study investigates how disorder affects helium-4 condensation in aerogels, revealing a disorder-induced phase transition in one type of aerogel but not the other, aligning with theoretical predictions.

Contribution

It provides experimental evidence for a disorder-induced phase transition in helium-4 condensation within aerogels, influenced by microstructural disorder.

Findings

Disorder induces a phase transition in helium-4 condensation.

The transition depends on the aerogel's microstructure and synthesis pH.

No transition observed in less disordered aerogel.

Abstract

We report on thermodynamic and optical measurements of the condensation process of $^4$He in two silica aerogels of same porosity 95%, but different microstructures resulting from different pH during synthesis. For a base-catalyzed aerogel, the temperature dependence of the shape of adsorption isotherms and of the morphology of the condensation process show evidence of a disorder induced transition,in agreement with recent theoretical predictions. This transition is not observed for a neutral-catalyzed aerogel, which we interpret as due to a larger disorder in this case.