Swarming in the Dirt: Ordered Flocks with Quenched Disorder

Area of Science:

• Statistical physics of active matter
• Condensed matter physics
• Disordered systems

Background:

• Quenched disorder significantly impacts collective motion in physical systems.
• Equilibrium ferromagnets exhibit limited order in the presence of disorder.
• Understanding active matter's response to disorder is crucial for its applications.

Purpose of the Study:

• To analyze the effect of quenched disorder on the collective motion of active particles.
• To compare the robustness of active polar systems against disorder with equilibrium ferromagnets.
• To investigate the impact of spatial dimensions on order in disordered active systems.

Main Methods:

• Theoretical analysis of active polar systems.
• Comparison with established theories for equilibrium ferromagnets.
• Numerical simulations to validate theoretical predictions in two dimensions.

Main Results:

• Active polar systems demonstrate superior robustness against quenched disorder.
• Long-ranged order (non-zero average velocity) persists in 3D active systems with disorder.
• Quasi-long-ranged order is observed in 2D active systems, while equilibrium systems show short-ranged order.

Conclusions:

• Active polar systems possess inherent mechanisms for maintaining collective motion under disorder.
• The findings challenge conventional understanding of order in disordered systems.
• Theoretical predictions for 2D systems are experimentally supported by simulations.