Georg-August-Universität Göttingen, Germany
Athermal aging and shear ordering in passive and active matter
In the first part of the talk I will consider the dynamics of a densely jammed, athermal assembly of repulsive soft particles. Starting from a random initial condition, we find nontrivial slow dynamics or “aging”, driven by a gradual release of stored elastic energy, with typical particle speeds decaying as a power law in time with a fractional exponent. This decay is accompanied by spatially localized and temporally intermittent “hot spots” of nonaffine deformation, connected by long-ranged swirls in the velocity field; the pattern of hot spots progressively coarsens, with the hot-spot size and separation slowly growing over time. We will then extend the framework to active particles that can model confluent tissues or self propelled colloids, and show that these exhibit rich aging behaviour: short persistence times of the active forcing lead to effective thermal aging while in the opposite limit one finds a two-step aging process, with active athermal aging at short times followed by activity-driven aging at late times. I will conclude with an outlook towards intriguing ordering phenomena of such active materials under shear.