Two step melting of the Weeks-Chandler-Anderson system in two dimensions

TL;DR

This study uses numerical simulations to explore the two-step melting process in a two-dimensional Weeks-Chandler-Anderson particle system, revealing a continuous solid-hexatic transition and a first-order hexatic-liquid transition.

Contribution

It provides detailed numerical evidence for the two-step melting process in 2D WCA systems, confirming the KTHNY scenario and characterizing defect formation at phase interfaces.

Findings

Solid-hexatic transition is continuous and follows KTHNY theory.

Hexatic-liquid transition is first order with defect string formation.

The melting process involves dislocation unbinding and defect interface dynamics.

Abstract

We present a detailed numerical simulation study of a two dimensional system of particles interacting via the Weeks-Chandler-Anderson potential, the repulsive part of the Lennard-Jones potential. With reduction of density, the system shows a two-step melting: a continuous melting from solid to hexatic phase, followed by a a first order melting of hexatic to liquid. The solid-hexatic melting is consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario and shows dislocation unbinding. The first order melting of hexatic to fluid phase, on the other hand, is dominated by formation of string of defects at the hexatic-fluid interfaces.