Resolving structural transitions in spherical dust clusters

TL;DR

This paper investigates structural transitions in finite spherical dust clusters, revealing complex melting behaviors and proposing a novel criterion based on distribution functions and entropy, applicable to experimental plasma systems.

Contribution

It introduces a new melting criterion based on distribution functions and entropy to analyze inhomogeneous Coulomb systems in traps, highlighting multiple types of melting.

Findings

Identification of radial melting, intrashell disordering, and inter-shell angular melting.

Development of a melting criterion based on reduced entropy.

Application of the criterion to complex plasma experiments.

Abstract

Finite systems in confining potentials are known to undergo structural transitions similar to phase transitions. However, these systems are inhomogeneous, and their "melting" point may depend on the position in the trap and vary with the particle number. Focusing on three-dimensional Coulomb systems in a harmonic trap a rich physics is revealed: in addition to radial melting we demonstrate the existence of intrashell disordering and inter-shell angular melting. Our analysis takes advantage of a novel melting criterion that is based on the spatial two and three-particle distribution functions and the associated reduced entropy which can be directly measured in complex plasma experiments.