Experimental observation of the marginal glass phase in a colloidal glass

Abstract

The replica theory of glasses predicts that in the infinite dimensional mean field limit, there exist two distinct glassy phases of matter: stable glass and marginal glass. We have developed a technique to experimentally probe these phases of matter using a colloidal glass. We avoid the difficulties inherent in measuring the long time behavior of glasses by instead focusing on the very short time dynamics of the ballistic to caged transition. We track a single tracer particle within a slowly densifying glass and measure the resulting mean squared displacement (MSD). By analyzing the MSD, we find that upon densification, our colloidal system moves through several states of matter. At lowest densities, it is a subdiffusive liquid. Next, it behaves as a stable glass, marked by the appearance of a plateau in the MSD whose magnitude shrinks with increasing density. However, this shrinking plateau does not shrink to zero; instead, at higher densities, the system behaves as a marginal glass, marked by logarithmic growth in the MSD toward that previous plateau value. Finally, at the highest experimental densities, the system returns to the stable glass phase. This provides direct experimental evidence for the existence of a marginal glass in three dimensions.

Determining the nonequilibrium criticality of a Gardner transition via a hybrid study of molecular simulations and machine learning

“…According to the mean-field theory that is exact in large dimensions, it is a second-order phase transition separating the simple glass phase and the Gardner phase where the free energy basin splits into many marginally stable subbasins (2). In structural glasses, the Gardner transition occurs deep in the glass phase below the liquid-glass transition temperature, which is observable even under nonequilibrium conditions (5)(6)(7)(8)(9)(10)(11)(12)(13) and has important consequences on the rheological and mechanical properties of the material (11,12,14), as well as on the jamming criticality at zero temperature (15). From a theoretical viewpoint, the Gardner transition universality class contains other important cases such as the famous de Almeida-Thouless transition in spin glasses (16).…”

Gardner physics in amorphous solids and beyond

“…One thus expects a logarithmic growth of the mean squared displacement with lag time. Intriguingly, a first study in this direction finds that glassy colloidal suspensions exhibit just such a transition from simple caged behavior to having logarithmically growing mean squared displacement 88 .…”

Experimental observations of marginal criticality in granular materials

“…The experimental verification of the marginal criticality of jamming is rare. Indirect characterizations of Gardner phase through particle dynamics has been performed in model glass systems, such as the cage separation upon compression in vibrated granular matter [29,30], and the logarithmic growth of the mean square displacement in colloidal glass [31]. Yet, direct quantitatively verification of the critical exponents of the fullRSB theory [3,4] and the relationship between the weak force exponents and the small gap exponent [5,7,8] in experiments is still lacking.…”