Anomalous grain dynamics and grain locomotion of odd crystals

TL;DR

This paper develops a phase field crystal model to study odd elastic behaviors in chiral crystals, revealing mechanisms behind anomalous grain dynamics, including self-rotation, self-fission, and transitions in grain coarsening.

Contribution

It introduces a continuum density field theory incorporating transverse interactions and odd elasticity, bridging microscopic and mesoscopic scales, to explain complex grain behaviors in active odd elastic materials.

Findings

Identification of surface cusp instability caused by odd stress leading to grain self-fission.

Prediction of a transition from normal to reverse Ostwald ripening in self-rotating grains.

Demonstration of controlling grain locomotion pathways by varying interparticle transverse interactions.

Abstract

Crystalline or polycrystalline systems governed by odd elastic responses are known to exhibit complex dynamical behaviors involving self-propelled dynamics of topological defects with spontaneous self-rotation of chiral crystallites. Unveiling and controlling the underlying mechanisms require studies across multiple scales. We develop such a type of approach that bridges between microscopic and mesoscopic scales, in the form of a phase field crystal model incorporating transverse interactions. This continuum density field theory features two-dimensional parity symmetry breaking and odd elasticity, and generates a variety of interesting phenomena that agree well with recent experiments and particle-based simulations of active and living chiral crystals, including self-rotating crystallites, dislocation self-propulsion and proliferation, and fragmentation in polycrystals. We identify a distinct type of surface cusp instability induced by self-generated surface odd stress that results in self-fission of single-crystalline grains. This mechanism is pivotal for the occurrence of various anomalous grain dynamics for odd crystals, particularly the predictions of a transition from normal to reverse Ostwald ripening for self-rotating odd grains, and a transition from grain coarsening to grain self-fragmentation in the dynamical polycrystalline state with an increase of transverse interaction strength. We also demonstrate that the single-grain dynamics can be maneuvered through the variation of interparticle transverse interactions. This allows to steer the desired pathway of grain locomotion and to control the transition between grain self-rotation, self-rolling, and self-translation. Our results provide insights for the design and control of structural and dynamical properties of active odd elastic materials.