Topological Defects and Non-homogeneous Melting of Large 2D Coulomb Clusters

TL;DR

This study uses Monte Carlo simulations to explore how large 2D Coulomb clusters with harmonic confinement develop topological defects and undergo non-uniform melting, revealing multiple melting temperatures linked to defect regions.

Contribution

It provides detailed insight into the defect structures and non-homogeneous melting behavior of large 2D Coulomb clusters, highlighting the role of topological defects in the melting process.

Findings

Formation of hexagonal lattice in the center with ring arrangements at the edges.

Presence of topological defects such as dislocations and disclinations.

Identification of three distinct melting temperatures corresponding to different regions.

Abstract

The configurational and melting properties of large two-dimensional clusters of charged classical particles interacting with each other via the Coulomb potential are investigated through the Monte Carlo simulation technique. The particles are confined by a harmonic potential. For a large number of particles in the cluster (N>150) the configuration is determined by two competing effects, namely in the center a hexagonal lattice is formed, which is the groundstate for an infinite 2D system, and the confinement which imposes its circular symmetry on the outer edge. As a result a hexagonal Wigner lattice is formed in the central area while at the border of the cluster the particles are arranged in rings. In the transition region defects appear as dislocations and disclinations at the six corners of the hexagonal-shaped inner domain. Many different arrangements and type of defects are possible as metastable configurations with a slightly higher energy. The particles motion is found to be strongly related to the topological structure. Our results clearly show that the melting of the clusters starts near the geometry induced defects, and that three different melting temperatures can be defined corresponding to the melting of different regions in the cluster.