Experimental observation of the marginal glass phase in a colloidal glass

TL;DR

This study experimentally observes the transition from liquid to stable glass and then to marginal glass in a colloidal system, providing direct evidence for the marginal glass phase predicted by replica theory.

Contribution

First experimental demonstration of the marginal glass phase in three dimensions using colloidal particles and short-time dynamics analysis.

Findings

Identification of sub-diffusive liquid behavior at low densities

Observation of a shrinking plateau indicating stable glass formation

Detection of logarithmic MSD growth characteristic of marginal 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 sub-diffusive 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 towards 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 3d.