Traveling and resting crystals in active systems

Area of Science:

• Physics
• Materials Science
• Soft Matter Physics

Background:

• Crystallization describes the process of forming ordered solid structures from disordered phases.
• Active systems, composed of self-propelled particles, exhibit unique dynamic behaviors not seen in equilibrium systems.
• Existing models like the phase-field-crystal (PFC) model describe freezing, while Toner-Tu theory addresses self-propelled particle dynamics, but a unified approach is lacking.

Purpose of the Study:

• To develop a unified microscopic field theory for crystallization in active systems.
• To predict and characterize novel active crystalline states.
• To explore the transition from resting to traveling crystalline states driven by self-propulsion.

Main Methods:

• A microscopic field theory was developed, integrating the phase-field-crystal model with the Toner-Tu theory.
• Theoretical predictions were made regarding the behavior of active crystalline systems.
• The study focused on characterizing different active crystalline states and transitions.

Main Results:

• The theory predicts a variety of active crystalline states.
• A key finding is the transition from a resting crystal to a traveling crystalline state as self-propulsion strength increases.
• In the traveling crystalline state, particles exhibit collective migration while preserving crystalline order.

Conclusions:

• The proposed theory provides a unified framework for understanding crystallization in active systems.
• The predicted traveling crystalline states offer new possibilities for active materials.
• The findings are verifiable through experiments and particle-resolved simulations, guiding future material design.