Symmetry Breaking and Topological Defect Formation in Ion Coulomb Crystals

TL;DR

This paper demonstrates the first clear observation of the Kibble-Zurek mechanism in ion Coulomb crystals, showing how defect density scales with transition rate during symmetry-breaking phase transitions in a controlled setting.

Contribution

It provides the first experimental verification of KZM scaling in an inhomogeneous system using ion Coulomb crystals, highlighting the role of causality and critical front propagation.

Findings

Defect density scales with transition rate as predicted by KZM

Inhomogeneous systems show steeper defect scaling

Controlled ion Coulomb crystals enable precise tests of phase transition dynamics

Abstract

Symmetry breaking phase transitions play an important role in nature. When a system traverses such a transition at a finite rate, its causally disconnected regions choose the new broken symmetry state independently. Where such local choices are incompatible, defects will form with densities predicted to follow a power law scaling in the rate of the transition. The importance of this Kibble-Zurek mechanism (KZM) ranges from cosmology to condensed matter [1-4]. In previous tests in homogeneous systems, defect formation was seen, but weak dependence on the transition rate and limited control of external parameters so far prevented tests of KZM scaling. As recently predicted [5-9], in inhomogeneous systems propagation of the critical front enhances the role of causality and steepens scaling of defect density with the transition rate. We use ion Coulomb crystals in a harmonic trap to demonstrate, for the first time, scaling of the number of topological defects with the transition rate - the central prediction of KZM - in a well-controlled environment.