When Soft Crystals Defy Newton's Third Law: Nonreciprocal Mechanics and Dislocation Motility

Area of Science:

• Soft matter physics
• Condensed matter physics
• Non-equilibrium statistical mechanics

Background:

• Effective interactions in driven soft matter systems often violate Newton's third law.
• Equilibrium systems adhere to Newton's third law, where forces are action-reaction pairs.
• Understanding non-equilibrium mechanics is crucial for novel material properties.

Purpose of the Study:

• To investigate the emergence of new mechanical behaviors in elastic crystals subjected to nonreciprocal interactions.
• To identify and classify the distinct classes of mechanics arising from these interactions.
• To explore the impact of violated Newton's third law on lattice defects like dislocations.

Main Methods:

• Theoretical modeling of elastic crystals with nonreciprocal interactions.
• Numerical simulations to observe system dynamics and emergent properties.
• Analysis of deformation mechanics and defect behavior beyond linear approximations.

Main Results:

• Six distinct classes of mechanics, absent in equilibrium systems, were identified.
• Nonreciprocal interactions fundamentally alter the mechanics of elastic crystals.
• Quiescent dislocations become mobile singularities, gliding through periodic lattices due to violated Newton's third law.

Conclusions:

• Driven soft matter with nonreciprocal interactions exhibits unique mechanics not found in equilibrium.
• The emergence of mobile dislocations is a direct consequence of interactions defying Newton's third law.
• This research opens new avenues for understanding and designing materials with active and responsive properties.