Physics Colloquium: From the glass transition to creep flows

Prof. Matthieu Wyart, École Polytechnique Fédérale de Lausanne (EPFL)

Abstract: Under cooling, a supercooled liquid undergoes a glass transition and stops flowing. Physicists do not agree on the microscopic reasons that make a glass solid. Some view this phenomenon as being collective in nature: it may be a signature of a thermodynamic phase transition, or  being caused by kinetic constraints (where particles seek to solve a sort of Chinese puzzle). Others view it as simply reflecting elementary barriers for rearrangements, controlled by the elasticity of the material. Here I will introduce a novel algorithm to systematically extract elementary rearrangements in a broad energy range. It allows to verify a quantitative prediction on the relaxation time, assuming that relaxation is not collective in nature. I will also propose a  theory of dynamical correlations in liquids based on coupled local rearrangements,  which connects this phenomenon  to avalanche-type responses observed in driven disordered materials. I will discuss connections between this view and recent measurement of sound emission in the creep response of  crumpled papers.

Bio: Matthieu Wyart is a French physicist. He is professor of physics at EPFL (École Polytechnique Fédérale de Lausanne) and the head of the Physics of Complex Systems Laboratory. Wyart’s research encompassed field such as the architecture of allosteric materials, the theory of deep learning, the elasticity and mechanical stability in disordered solids, the granular and suspension flows, the glass and rigidity transitions, the marginal stability at random close packing and other glasses, and the yielding transition. More recently his work has focused on machine learning, in particular data structure and generative models. M. Wyart is the recipient of the Simons Investigator Award, the Sloan Fellowship, the G. Carrier Fellowship, the Dresden Physics prize and is a fellow of the American Physical Society.