Flocking through disorder

We address the robustness of flocking motion to challenging environments.
The emergence of collective motion in groups of motile bodies arises from the competition between rotational diffusion and polar interactions in ensemble of active particles.This minimal picture was successfully employed to account for the large scale dynamics of systems as diverse as starling flocks and self-propelled colloids.
Building on model experiments based on Quincke rollers, I will show how colloidal flocks lose their orientational order when cruising through disordered lattices. I will present a series of quantitative experiments that elucidate the existence of a novel state of active matter that supports orientational order (through a sparse rivers network) but no net transport. In particular, I will show that this state can be seen as a glass of topological defects.