Structure-dynamics relationship in ratcheted colloids: Resonance melting, dislocations, and defect clusters

TL;DR

This study investigates how a ratcheted colloidal system undergoes a non-equilibrium melting transition driven by resonance effects, revealing the role of dislocations and defect clusters in the process.

Contribution

It provides a detailed phase diagram and insights into the defect-mediated continuous melting transition in a driven colloidal system.

Findings

Resonance between ratcheting frequency and system relaxation causes melting.

Melting transition is continuous, from solid to hexatic phase.

Dislocations and defect clusters mediate the transition.

Abstract

We consider a two dimensional colloidal dispersion of soft-core particles driven by a one dimensional stochastic flashing ratchet that induces a time averaged directed particle current through the system. It undergoes a non-equilibrium melting transition as the directed current approaches a maximum associated with a resonance of the ratcheting frequency with the relaxation frequency of the system. We use extensive molecular dynamics simulations to present a detailed phase diagram in the ratcheting rate-mean density plane. With the help of numerically calculated structure factor, solid and hexatic order parameters, and pair correlation functions, we show that the non-equilibrium melting is a continuous transition from a quasi-long ranged ordered solid to a hexatic phase. The transition is mediated by the unbinding of dislocations, and formation of compact and string-like defect clusters.