Shear-induced Fickian yet non-Gaussian diffusion in athermal jammed matter

Initially observed for colloidal tracers in complex fluids, Fickian yet non-Gaussian diffusion (FnGD) has since emerged in a wide range of thermal and active systems, revealing its ubiquitous nature when particles move in heterogeneous environments. Here we show that FnGD can occur even for particles immune to thermal motion, by investigating a model of soft jammed matter sheared at constant rate. On varying the shear rate γ ̇ γ ° and the volume fraction ϕ , we find that the statistics of non-affine single-particle displacements obey robust master curves, with dependence on γ ̇ γ ° and ϕ controlled only by three shifting factors related to characteristic time- and length-scales of microscopic dynamics. Shear-induced FnGD emerges near the onset of the apparent decoupling between shear stress and shear rate characterizing the yielding rheology of soft jammed solids, and extends over increasingly broad time windows on decreasing γ ̇ γ ° . A minimal Heterogeneous Persistent Random Walk model captures the emerging dynamical features in terms of domain-dependent persistence times and finite renewal time of the local environment. Overall, our results reveal the existence of FnGD in non-thermal systems and contribute to a better understanding of the rheology of soft jammed matter.