The yielding transition of soft colloids

We investigate the yielding transition of dense suspensions of colloids interacting via a soft repulsive potential by simultaneously measuring their mechanical response and microscopic dynamics under an oscillating shear deformation.
At low strain amplitude, all systems exhibit ultraslow, ballistic dynamics characterized by a compressed exponential relaxation of correlators, similar to those reported for many jammed soft materials at rest. Upon increasing the strain amplitude, in correspondence to the onset of the non-linear rheological response, we observe a dynamic transition towards a steady state characterized by fast stretched exponential, diffusive-like relaxations, reminiscent of those measured in supercooled liquids at rest.
Although the sharpness of the transition depends on the potential details, this scenario seems to be generic to soft colloids. We show that its main features are captured by an Ising-like model, with dynamic facilitation coupling the relaxation of neighboring sites, and we discuss intriguing analogies with thermodynamic phase transitions.