Particle deformability stabilizes hexatic order and suppresses crystallization

TL;DR

This study demonstrates that deformable particles in two-dimensional systems favor a hexatic phase over a solid phase during phase transitions, due to entropy effects and strain accommodation mechanisms, altering traditional phase behavior.

Contribution

It reveals that particle deformability prevents solid formation, promoting a stable hexatic phase and providing a new understanding of phase transitions in soft and biological materials.

Findings

Hexatic phase is thermodynamically favored over solid at low temperatures.

Deformability suppresses dislocation condensation, hindering solid formation.

System accommodates strain through particle shape changes, affecting defect energetics.

Abstract

We show that two-dimensional systems of deformable particles undergo a continuous liquid-hexatic transition upon compression or cooling, but no hexatic-solid transition-even at zero temperature and high density. Numerical simulations reveal that solid-like configurations do not possess a lower energy than hexatic ones, so that at low temperatures the hexatic phase is thermodynamically favored due to its higher entropy. Dislocation condensation, necessary for solid formation, is suppressed as the system accommodates strain via particle shape changes, responding affinely to compression. Our findings identify a generic route by which microscopic mechanical properties control defect energetics and reshape phase behavior in two dimensions, with broad relevance for soft and biological materials such as microgels and epithelial tissues.