# Reentrant melting of scarred odd crystals by self-shear

## TL;DR

This study shows how confinement-induced defects in active materials can cause unexpected melting and self-shearing behaviors.

## Contribution

The paper introduces reentrant melting in odd elastic solids due to chiral activity and grain boundary scars.

## Key findings

- Grain boundary scars decouple edge flows from the bulk in confined spinner assemblies.
- Increased chiral activity leads to spontaneous self-shearing and reentrant melting.
- Topological defects reshape flow behavior in odd elastic solids.

## Abstract

Spatial confinement can induce geometrical frustration in condensed phases, giving rise to topological defects that confer materials with new and exotic properties. Here, we experimentally uncover the effect of confinement-induced defect strings termed ‘grain boundary scars’ on the behavior of dense two-dimensional assemblies of granular spinners, a canonical odd elastic solid. The spatial arrangement of these scars fundamentally reshapes the flows triggered by chiral activity. Specifically, they cause the topologically protected edge flows - a ubiquitous feature of confined spinner assemblies - to decouple from the bulk. Strikingly, increasing the net chiral activity of the system by tuning the ratio of counterclockwise to clockwise spinners caused spontaneous self-shearing. The resulting odd radial stresses led to a chiral activity-mediated reentrant melting transition at a fixed areal spinner density. Our findings open new avenues for exploiting geometrical frustration to elicit novel responses from odd elastic solids.

Geometrical frustration in confined systems can lead to the emergence of topological defects, which significantly influence the physical properties of materials. This study demonstrates that grain boundary scars in dense assemblies of active spinners can decouple edge flows from the bulk, resulting in spontaneous self-shearing and a chiral activity-mediated reentrant melting transition.