Inhomogeneous melting in anisotropically confined two-dimensional clusters

Molecular dynamic simulations are performed to investigate the melting process of two-dimensional clusters of classical charged particles trapped in an anisotropic parabolic potential. The confined particles interact through a repulsive potential. We find that the eccentricity of the confinement potential strongly affects the melting pattern of such clusters. Increasing the eccentricity of the confinement potential drives the system through three different melting regimes. Inhomogeneous melting is the typical melting process for anisotropically confined clusters and its appearance in small systems occurs in a distinct form called here internal intershell melting. The latter involves only particles in the center of the cluster while particles on the far left and right of the cluster are still ordered having a much higher melting temperature. Using the Lindemann's criterion the melting temperatures are determined as a function of the different parameters. The internal intershell melting process is found for both long-range (i.e., logarithmic) and short-range (i.e., screened Coulomb) interparticle interaction. Decreasing the range of the interparticle interaction increases the eccentricity of the confinement potential for which internal intershell melting can occur.