COULOMB CLUSTERS - MELTING AND POTENTIAL BARRIERS

The melting of two-dimensional and three-dimensional Coulomb micro-and macroclusters is studied. Temperature dependences of radial and angul ar square deviations of particles are investigated. The melting of mic roclusters has two stages. at lower temperature there is a transition from a frozen phase to a state with a rotatory reorientation of ''crys talline'' shells relative to each other, different pairs of shells mel ting at different temperatures. In the case of large N and high triang ular symmetry inside the cluster, orientational melting takes place on ly for external pairs of shells. In this case external shells lose the ir order. At higher temperature a transition with a loss of radial she ll order occurs. The origin of two-stage melting is in the smallness o f the barrier energy relative to the rotation of shells in comparison with the barrier corresponding to the radial disordering of shells. It is shown also that the temperatures of orientational and total meltin g are at 5-15 times lower than the temperatures of disappearance of co rresponding potential barriers. The influence of confinement anisotrop y on the character of cluster melting is considered. It is found that at some degree of anisotropy the melting becomes one stage. The last i s connected with an increase of the ratios of barriers of intershell r otation to barriers of jumps of a particle between the shells. (C) 199 8 Elsevier Science B.V.