Heterogeneous Dynamics and Internal Stress Distributions near Dislocation Jamming

Dislocation assemblies in crystalline substrates represent a new example of the broad class of systems that exhibit a jamming (or yielding) transition. Rheology experiments carried out on this broad class of systems ranging from granular media to foams show that their dynamics becomes increasingly heterogeneous when approaching the jamming threshold. Likewise, experiments on crystal plasticity at various scales have recently emphasized the heterogeneous character of plastic flow. Crystal dislocations move in a intermittent manner as a result of the combined effects of kinetic constraints and long range anisotropic dislocation interactions, which together may induce metastable jammed dislocation configurations. Building up upon these premises, here we explore further the analogy between simple two-dimensional dislocation ensembles and other systems exhibiting jamming, by considering the behavior of the so-called dynamic four point susceptibility X-4(1,tau), as well as the shear stress distributions in both jammed and moving dislocation arrangements. Our results on the behavior of X-4(1,tau) point towards the existence of a growing dynamic correlation length as the jamming threshold is approached within the moving phase. Moreover, the topology of the shear stress distributions for the dislocation arrangements seem to corroborate this picture, showing increasingly broad size distributions and correlation lengths of stress clusters near dislocation jamming.