Structured randomness: jamming of soft discs and pins

Area of Science:

• Physics
• Materials Science
• Computational Science

Background:

• Understanding jamming in granular materials and soft matter is crucial.
• The jamming transition marks the onset of rigidity in disordered systems.
• The effect of geometric constraints, like pinning sites, on jamming is not fully understood.

Purpose of the Study:

• To investigate the zero-temperature jamming threshold (φj) of soft, bidisperse disks with lattice-arranged fixed particles (pins).
• To analyze the structural properties of the system near the jamming threshold as a function of pin density.
• To explore the emergence of order and its correlation with the pin lattice structure.

Main Methods:

• Utilizing computational simulations to model soft, bidisperse disks.
• Introducing fixed particles (pins) in a lattice arrangement to systematically vary pin density.
• Calculating structural properties, including correlation length and bond orientational order, near the jamming threshold.

Main Results:

• The jamming threshold (φj) decreases with the introduction of pins.
• The correlation length exponent remains ν = 1/2 at low pin densities.
• The system exhibits enhanced mechanical stability with more bonds but fewer contacts than predicted by the Maxwell criterion in the absence of pins.
• Increasing pin density leads to the emergence of novel bond orientational order and long-range spatial order, correlated with the pin lattice's square symmetry.

Conclusions:

• Fixed particles significantly alter the jamming behavior of soft disk systems.
• The presence of pins induces structural order and modifies mechanical stability beyond simple density effects.
• The observed order is directly linked to the symmetry of the underlying pin lattice, offering insights into geometrically constrained jamming.