Nanofriction and motion of topological defects in self-organized ion Coulomb crystals

TL;DR

This paper investigates nanofriction phenomena in ion Coulomb crystals with topological defects, revealing how defect dynamics influence the pinning-sliding transition and mode softening through experimental and numerical analysis.

Contribution

It provides new insights into how topological defects affect nanofriction and the sliding transition in ion Coulomb crystals, combining experimental measurements with simulations.

Findings

Identification of the transverse vibrational soft mode signaling the sliding transition

Demonstration of symmetry breaking effects on mode softening

Analysis of defect properties and their influence on the crystal dynamics

Abstract

We study nanofriction in an ion Coulomb crystal under the presence of topological defects. We observe signatures of the pinning to sliding transition, namely the transverse vibrational soft mode signaling the transition and the symmetry breaking of the crystal configuration. We present details on experimental measurements and numerical simulations of this system, including the gaps in the hull function and the spectroscopy of the localized defect mode. We also investigate how external forces, such as those due to anharmonic potentials or differential light pressure, break the intrinsic crystal symmetry, thereby reducing mode softening near the sliding transition. We find that the local structure and position of the topological defect is essential for the presence of the soft mode and illustrate how the defect changes its properties, when it moves through the crystal.