Active Breathing Particles: Unjamming and Rheology

We investigate the behaviour of "active breathing particles", i.e. particles with actively deforming radii, using microscopic simulations. In the absence of an external drive, there exists a threshold breathing amplitude for large-scale plasticity in the system. The overall elastoplastic behaviour of the system is similar to cyclically sheared systems. Observations on the memory of activity stored in the system have analogies with memory retention in amorphous solids under macroscopically applied cyclic shear. In the presence of an external shear, the mechanical response confirms loss of rigidity around the aforementioned threshold amplitude, and hence we observe two different branches of the flow-curves above and below the threshold amplitude, one pertaining to a yield stress solid and the other a fluid.