Transmission of mobility via cooperative mechanisms in soft active matter

When supercooled, liquids viscosity increases dramatically as the glass transition temperature is approached. While the physical origin of this behavior is still not understood, it is now well established that the addition of a few activated particles is able to reverse that increase in viscosity. Here we further raise the question of a limit in that fluidization process and of the differences between the fluidized liquid and its viscous counterpart. Results show that a few percent active molecules are enough to trigger a phase transition leading to diffusion coefficients typical of liquids while the medium retains cooperative properties of the viscous phase. The similarity between cooperative properties of the active and non active molecules suggests that the mobility of active molecules is transmitted to inactive ones via the medium cooperative mechanisms, a result in agreement with facilitation theories. This result is then confirmed by the compared behavior of the distinct van hove correlation functions of most mobile active and non active molecules. Interestingly enough, in our simulations the cooperative mechanisms are not induced or related to a decrease of the excitation concentration.