Alignment destabilizes crystal order in active systems

Area of Science:

• Soft Matter Physics
• Condensed Matter Theory
• Active Matter Physics

Background:

• Active crystals, composed of self-propelled units, exhibit unique collective behaviors distinct from equilibrium systems.
• Understanding the interplay between particle interactions and emergent order is crucial for active matter research.

Purpose of the Study:

• To investigate the phase behavior and ordering properties of two-dimensional active crystals with permanent links.
• To analyze the influence of two distinct alignment interactions (Vicsek-like and elasticity-based) on crystal order.
• To generalize findings to higher dimensional systems.

Main Methods:

• Combined numerical simulations and analytical techniques.
• Studied systems with permanently linked swimmers.
• Investigated two types of alignment interactions: Vicsek-like and elasticity-based.

Main Results:

• Identified a stationary phase with quasi-long-range translational order.
• Characterized a moving phase with quasi-long-range active force director and velocity order.
• Demonstrated that alignment interactions critically affect translational order in the moving phase: Vicsek-like alignment leads to short-range translational and quasi-long-range bond-orientational order (moving hexatic phase), while elasticity-based alignment results in quasi-long-range translational order parallel to motion and long-range bond-orientational order.

Conclusions:

• Active crystals exhibit rich phase behavior dependent on alignment interactions.
• The study provides a framework for understanding order in active crystalline systems.
• Findings are generalizable to higher dimensions, offering insights into broader active matter phenomena.