Segregation via Species Heterogeneity: Dynamical Phases in a Two-Species Model of Active Brownian Particles

Heterogeneity denotes variability among the components of a system, spanning from chemical heterogeneity of macromolecules forming membraneless organelles of eukaryotic cells to different animal species in ecological systems, such as schools of fishes and flocks of birds. A particularly relevant form of diversity is phenotypic heterogeneity, which refers to variations in traits or behaviors among genetically identical individuals and can potentially provide evolutionary advantages. In this context, understanding how phenotypic heterogeneity among active agents influences collective behavior, i.e. the organized macroscopic patterns emerging from interacting individuals, has become an increasingly important topic for active matter physics. This thesis aims at shedding light on the role of species heterogeneity by studying a typical class of active systems, self-propelled particles, that phase separate into a fluid and gaseous phase at sufficiently high density and propulsion speeds. Previous studies on this topic varied the interaction strength between species, showing the emergence of phase-separated bands dominated by a single species, and mixed species with different self-propulsion, leading to emergent herd-avalanche mechanisms. This work builds upon the research by mixing two interacting species with distinct persistence, while fixing their propulsion speed. We find that the individuals exhibit phase separation only when the persistence time of the less persistent species exceeds a critical value.