Trapping of Topological-Structural Defects in Coulomb Crystals

TL;DR

This study investigates the formation, dynamics, and trapping of topological defects ('kinks') in Coulomb crystals of ions, combining experimental observations with theoretical simulations to understand their behavior and confinement.

Contribution

It demonstrates the creation of topological defects in two-dimensional Coulomb crystals and reveals their unique dynamical features and trapping mechanisms.

Findings

Kinks are always observed at the trap center.

The probability of kink formation saturates at approximately 50%.

Simulations show strong anharmonicity in the kink's internal mode.

Abstract

We study experimentally and theoretically structural defects which are formed during the transition from a laser cooled cloud to a Coulomb crystal, consisting of tens of ions in a linear radio frequency trap. We demonstrate the creation of predicted topological defects (`kinks') in purely two-dimensional crystals, and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the centre of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence surprisingly saturates at ~0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal.