How Activity Heterogeneity Influences Glass Transition

A jammed or glassy system can become fluidized when all particles are active, i.e., self-propelled. If the persistence time of the self-propelled force is fixed and within a certain range, the "active energy," which is proportional to the square of the self-propelled velocity, can be related to an effective temperature that aids in understanding fluidization. However, activity can be individually controlled at the particle level, distinct from macroscopic parameters, introducing another degree of heterogeneity. This study examines how activity heterogeneity affects the overall glassy dynamics. Specifically, the total "active energy" injected into the system is kept constant, while its spatial distribution is varied – either distributed uniformly among all particles or concentrated on a small fraction. Criteria are quantified to determine when a heterogeneous active system behaves similarly to a homogeneous one with equal active energy, and when activity heterogeneity begins to influence system behavior significantly. An explanation based on the influential zone of active particles on local glassiness and the interactions between these influential zones are proposed and quantitatively examined. How the size of influential zones is controlled by different parameters is also investigated.