Emergent Phases in High-Density Active Matter: From Velocity Alignment and Collective Excitations to Chiral Bubbles

by Lorenzo Caprini (Univ. Sapienze)

Tuesday 20 May 2025, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

Ordinary materials are termed passive because their constituents are inert particles that move only in response to thermal fluctuations, conservative interactions, or external fields. By contrast, active matter refers to systems composed of self-propelled units - such as swimming microorganisms, animals, self-propelling colloids, or autonomous robots - which extract energy from their surroundings to sustain directed or chiral motion. These systems are inherently out of equilibrium and often exhibit emergent collective behavior, including clustering and flocking. This talk focuses on high-density active matter, discussing spontaneous velocity alignment in active liquids and the emergence of non-equilibrium collective excitations in active crystals. I will also predict an unprecedented phase transition from a homogeneous to an inhomogeneous phase characterized by bubbles, which exhibit edge currents and vortices. This novel phenomenon, driven by chiral interactions, may be observed in chiral active systems such as spinning colloids or rotating chiral robots.