Self-Propelled Particles with Velocity Reversals and Ferromagnetic Alignment: Active Matter Class with Second-Order...

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Active matter systems exhibit complex behaviors, often involving phase separation before achieving orientational order.
• Understanding transitions in these systems is crucial for fields ranging from biology to materials science.

Purpose of the Study:

• To introduce and characterize a new class of dry, aligning active matter in two dimensions.
• To investigate the nature of the transition to orientational order in these systems.

Main Methods:

• Theoretical introduction of a new active matter model.
• Numerical simulations to study the phase transition dynamics.
• Analysis of scaling exponents and correlation functions.

Main Results:

• Observed a direct transition to orientational order, without prior phase separation.
• Systems display quasi-long-range polar order with continuously varying scaling exponents.
• The transition was identified as a standard critical point, not belonging to the Berezinskii-Kosterlitz-Thouless universality class.

Conclusions:

• The interplay between order and density significantly alters the role of defects in active matter systems.
• This work provides a new framework for understanding transitions in non-equilibrium systems.
• The findings challenge existing universality class assignments for active matter phase transitions.