Séminaire

Mardi 28 Mai 2019 à 11h00.

A new amorphous phase of matter

''Despite being widely used for various applications, the fundamental nature of amorphous solids, such as granular matter, foams, emulsions, dense colloidal pastes, molecular and atomic glasses, is still unclear. The goal is to describe theoretically how their macroscopic properties (transport, vibrational, mechanical, etc.) arise from their disordered microscopic structure. To that aim, an exact mean field theory for glasses was recently derived. The solution surprisingly revealed existence of a new amorphous phase of matter, called the Gardner phase. The mathematical description of this phase reflects a complex and fragile structure: the solid responds in a violently nonlinear way to very weak perturbations, it evolves in time (aging) and involves rearrangements that propagate through the whole system by successive avalanches. This behavior is the one we seek to describe. I will present analytical and numerical results obtained with a simple glass-forming model. By changing external parameters, we continuously explore physical regimes relevant to granular matter, foams, emulsions, hard and soft colloids, and molecular glasses. I will discuss under which type of physical conditions this new amorphous phase of matter is found, and its implications for the behavior of the solid. Our results suggest that Gardner phase should be observable for colloidal and non-Brownian particles near their jamming transition. In this regime, we numerically observe spectacular rejuvenation and memory effects. By contrast, we find that molecular glasses do not present marginally stable phases, but our study reveals instead the presence of localised excitations presumably relevant for mechanical and low-temperature properties of structural glasses.''