The effective interaction potential between particles lies at the core of our understanding of the behavior of matter. In equilibrium, such interactions are the potential forces between the different constituents of the system and are time independent. In systems out of equilibrium, however, other kinds of interactions can emerge. Such is the case of active matter where cooperative phases appear due to the activity of the particles themselves, and not their equilibrium interaction potentials. In this talk we will present our work on emergent ultra long range attraction between active colloids in dense passive media. This long range interaction, which we name plastic attraction, has its origin on the elasticity of the system coupled with cooperative yielding events, also known as plastic deformation. Interestingly, the interaction range can be tuned, modified or completely suppressed by utilizing space and time dependent activity protocols. Another interesting system is when one of the species is pinned. In such an scenario, we find that spinning active particles undergo a disorder induce delocalization transition. Under some particular circumstances, one finds super diffusive states in highly disorder systems, indicating that underlying correlations of the particles may play a critical role in the dynamics of such particles. These results clarify the origin of phase separation in active matter systems and give insight into new avenues that can be explored in such systems.
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