Rounded hard squares confined in a circle

Area of Science:

• Condensed Matter Physics
• Materials Science
• Biophysics
• Statistical Mechanics

Background:

• Packing under confinement is key to understanding ordered structures via entropic effects.
• The impact of confinement on anisotropic particles, especially topological defects, is not well understood.
• Prior research shows granular rods in circular confinement form square-like super-particles with four disclinations.

Purpose of the Study:

• To investigate how circular confinement affects ordered structures of rounded-corner hard-squares with varying roundness.
• To explore the emergence of topological defect structures in confined anisotropic particles.

Main Methods:

• Utilized Monte Carlo simulations within the NPT ensemble.
• Studied rounded-corner hard-squares with systematically varied roundness parameters.
• Analyzed structural transitions and defect formation under circular confinement.

Main Results:

• At low roundness, particles formed a cross-shaped domain with tetratic order and four +1/4 disclinations.
• With increased roundness, a novel partition structure emerged: six domains with six +1/4 disclinations and a central -1/2 disclination.
• Demonstrated entropy-governed structural transitions driven by confinement geometry and particle shape.

Conclusions:

• The interplay between confinement and particle shape dictates self-assembly and structural transitions.
• Findings provide new insights for designing topological metamaterials with tunable properties.
• Highlights the role of entropy in driving complex ordered structures in confined systems.