Helium condensation in aerogel: avalanches and disorder-induced phase transition

TL;DR

This study numerically investigates helium condensation in silica aerogels, revealing avalanche phenomena and a disorder-induced phase transition with critical behavior akin to the Random Field Ising Model.

Contribution

It introduces a coarse-grained lattice-gas model to analyze nonequilibrium helium adsorption and identifies a critical line with universal scaling properties.

Findings

Avalanche size distribution follows a power-law at critical points.

Adsorption isotherms exhibit universal scaling near criticality.

Critical exponents align with the zero-temperature Random Field Ising Model.

Abstract

We present a detailed numerical study of the elementary condensation events (avalanches) associated to the adsorption of $^4$He in silica aerogels. We use a coarse-grained lattice-gas description and determine the nonequilibrium behavior of the adsorbed gas within a local mean-field analysis, neglecting thermal fluctuations and activated processes. We investigate the statistical properties of the avalanches, such as their number, size and shape along the adsorption isotherms as a function of gel porosity, temperature, and chemical potential. Our calculations predict the existence of a line of critical points in the temperature-porosity diagram where the avalanche size distribution displays a power-law behavior and the adsorption isotherms have a universal scaling form. The estimated critical exponents seem compatible with those of the field-driven Random Field Ising Model at zero temperature.