Condensation of Helium in Aerogel and Athermal Dynamics of the Random-Field Ising Model

Abstract

High resolution measurements reveal that condensation isotherms of (4)He in high porosity silica aerogel become discontinuous below a critical temperature. We show that this behavior does not correspond to an equilibrium phase transition modified by the disorder induced by the aerogel structure, but to the disorder-driven critical point predicted for the athermal out-of-equilibrium dynamics of the random-field Ising model. Our results evidence the key role of nonequilibrium effects in the phase transitions of disordered systems.

Statistical mechanics of unsaturated porous media

“…(4). Therefore, vapor pressure is not as crucial here as it is in analyses of hysteretic isotherms of sorption on nanometric porous structures [102][103][104][105].…”

A single-walker approach for studying quasi-nonergodic systems

“…In contrast to the JW MC simulations, both experimental studies 73,79 and single-flip MC simulations 80,81 are not able to access the equilibrium for sufficiently low temperatures due to presence of the hysteresis effect. Indeed, the results of the single-flip MC simulations for adsorption (solid lines in Fig.…”

“…it takes place at a lower pressure (or chemical potential) compared to the bulk saturation value 61,62 . While studies of fluids confined in single pores of simple geometry have clarified the mechanism for such shifted transitions [62][63][64][65][66] , the situation in real materials such as mesoporous glasses and silica gels, that consist of an interconnected network of pores of various shape and size, is still under active investigation [67][68][69][70][71][72][73][74] .…”

“…Therefore, obtaining the equilibrium isotherms for sorption in aerogel and other porous materials is often problematic, and requires techniques such as mean-field scanning curves 68 . However, despite those efforts conclusive answers have not yet been obtained to even the key questions such as about the existence of the discontinuous phase transition in aerogel samples of different porosity 73 . The JW algorithm is designed to avoid hysteresis and thus can be an invaluable tool in detecting phase transitions and resolving such problems.…”

Finite-dimensional vestige of spinodal criticality above the dynamical glass transition

“…More theoretically enticing than the Ising spinodal is that of models with disorder, which capture the essence of systems ranging from magnetic [8] to mesoporous [9,10] materials and also appear in social sciences and economics [11]. These models exhibit a rich set of activated processes, such as avalanches [8,12] and hopping [13,14], in addition to nucleation, which makes their criticality especially challenging to scrutinize.…”