Soft materials such as colloidal suspensions, emulsions, foams and gels often display complex and unusual behaviors compared with ordinary solids or liquids. From a mechanical point of view, for instance, they can resist deformation like solids, but they can also start to flow like liquids when a sufficiently strong external drive is applied. This transition from solid-like to liquid-like behavior, known as “yielding,” is central to the physics of soft amorphous materials and to many industrial and biological processes.

Some of these systems are also athermal: They are made of particles large enough that thermal motion plays no role in their dynamics. Their microscopic motion is therefore governed mainly by mechanical driving and interactions with neighboring particles, making their behavior even more unusual and intriguing.

A new study published in Communications Physics, establishes a connection between the mechanical yielding of soft athermal matter and a distinctive form of microscopic dynamics: Fickian yet non-Gaussian diffusion (FnGD). This phenomenon, also referred to as Brownian yet non-Gaussian diffusion, was first reported in 2009 and has since been identified in a variety of molecular systems, as well as in thermal and active soft matter, especially for particles moving in heterogeneous environments.