Shear-melting of a hexagonal columnar crystal by proliferation of dislocations

TL;DR

This study investigates shear-induced melting in a hexagonal columnar crystal, revealing that dislocation proliferation causes melting and suggesting the presence of a line hexatic phase under shear.

Contribution

It combines shear-thinning analysis with synchrotron X-ray scattering to link dislocation density with shear rate and proposes a new phase transition involving a line hexatic phase.

Findings

Dislocation density varies as shear rate to the 2/3 power.

Shear-melting occurs above a critical shear rate or stress.

Evidence for a line hexatic phase under shear.

Abstract

A hexagonal columnar crystal undergoes a shear-melting transition above a critical shear rate or stress. We combine the analysis of the shear-thinning regime below the melting with that of synchrotron X-ray scattering data under shear and propose the melting to be due to a proliferation of dislocations, whose density is determined by both techniques to vary as a power law of the shear rate with a 2/3 exponent, as expected for a creep model of crystalline solids. Moreover, our data suggest the existence under shear of a line hexatic phase, between the columnar crystal and the liquid phase.