Fingering Instability of Dislocations and Related Defects

TL;DR

This paper uncovers a fundamental instability in mobile dislocations and line defects in crystals, where a force gradient causes a fingering pattern, with the unstable wavelength depending on the force gradient, demonstrated through simulations.

Contribution

It introduces the concept of fingering instability in dislocations and related defects, linking force gradients to morphological instability, supported by molecular dynamics and model simulations.

Findings

Unstable fingering pattern caused by force gradient.

Minimum unstable wavelength scales as inverse square root of force gradient.

Demonstrated in simulations of dislocations and vortex lines.

Abstract

We identify a fundamental morphological instability of mobile dislocations in crystals and related line defects. A positive gradient in the local driving force along the direction of defect motion destabilizes long-wavelength vibrational modes, producing a ``fingering'' pattern. The minimum unstable wavelength scales as the inverse square root of the force gradient. We demonstrate the instability's onset in simulations of a screw dislocation in Al (via molecular dynamics) and of a vortex in a 3-d XY ``rotator'' model.