The last few years have seen an increasing interest of the statistical physics community in the study of the yielding phenomenon of a driven amorphous material. Foams, colloidal glasses, granular materials or bulk metallic glasses respond elastically when a small external strain is applied, but they yield and flow due to internal plastic rearrangements if the drive is large enough. The dynamical crossover between these two regimes can be understood as a dynamical phase transition and, in fact, it was shown to be accompanied by critical-like phenomena like growing correlation lengths and avalanches.
On the other hand, we assist to more than 30 years now in the development and understanding of the out-of-equilibrium driven phenomenon known as the depinning of elastic manifolds in random media. Systems such as magnetic and ferroelectric domain walls, contact lines in wetting, fracture fronts, and arrays of vortices in type-II superconductors, present a common phenomenology when we consider them as elastic objects embedded in a disordered medium and driven by an external force. If the external force is weak, the elastic object eventually gets pinned in the disordered landscape and its steady velocity is zero. If the force is strong enough, instead, the manifold will overcome even the largest pinning centers, reaching a steady state of mean finite velocity. This dynamical phase transition is well-documented in a literature that nowadays goes well beyond the depinning itself, describing also the equilibrium problem of the elastic line, thermally activated dynamical regimes, different effective elasticities and disorder types, the fast flow regime at large driving and, in all these cases, the relation between geometry and transport properties.
Given the enormous qualitative similarity between the yielding transition and the depinning transition (no-flow to flow when overcoming a critical threshold of external drive) people were tempted to categorize them in the same family of dynamical phenomena. Nevertheless, the differences among these two out-of-equilibrium transitions are not minor and forcing the analogy beyond its boundaries can constitute a misstep.
The
aim of this mini-workshop is to
dig into the similarities and differences between these two phenomena, trying to address questions such as:
Are yielding and depinning essentially the same dynamical phase transition? Shall we extrapolate the knowledge on depinning to the yielding scenario by mapping one to one physical quantities? To which extent should we expect universality in the yielding transition? Is there an equivalence between stress-driven and strain-driven protocols? How should we address them in simplified models? Which are the relevant transport properties of driven amorphous solids? Are they linked to geometrical properties as in elastic manifolds?
The workshop is organized as a part of the visit of Dr. Alejandro Kolton to LIPhy, founded by the CPTGA (Centre de Physique Théorique de Grenoble-Alpes).
