title: Premelting and postmelting in clusters.
abstract: Caloric curves for sodium clusters with N=139 and 147 atoms show a fine structure near the solid-to-liquid transition. Neither of the two sizes exhibit surface melting. For N=139, diffusion of the surface vacancies is observed, which is not possible in the closed-shell N=147 cluster. A few kelvin above the peak in the heat capacity, N=139 is completely liquid. This is not the case for N=147. Here the inner 13 atoms remain nearly fixed up to several tens of kelvin above the melting temperature of the outer two layers. A simple physical reason is suggested for this unexpected behavior.
authors.affiliation: Fakultät für Physik, Universität Freiburg, H. Herderstrasse 3, 79104 Freiburg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Hock
authors.forename: Christof
authors.initials: C
authors.lastname: Bartels
authors.forename: Samuel
authors.initials: S
authors.lastname: Strassburg
authors.forename: Martin
authors.initials: M
authors.lastname: Schmidt
authors.forename: Hellmut
authors.initials: H
authors.lastname: Haberland
authors.forename: Bernd
authors.initials: B
authors.lastname: von Issendorff
authors.forename: Andrés
authors.initials: A
authors.lastname: Aguado