Stick-Slip Nanofriction in Trapped Cold Ion Chains

TL;DR

This study uses simulations of trapped cold ion chains in optical lattices to explore how stick-slip friction behavior emerges and changes with structural transitions, revealing insights into nanoscale friction mechanisms.

Contribution

It introduces a novel simulation approach of ion chains to understand stick-slip friction and the effects of structural transitions on dynamic friction.

Findings

Transition from smooth to stick-slip sliding with increasing potential amplitude.

Precursor partial slips precede overall sliding, similar to macroscopic systems.

Structural transition from linear to zigzag increases dynamic friction.

Abstract

Stick-slip -- the sequence of mechanical instabilities through which a slider advances on a solid substrate -- is pervasive throughout sliding friction, from nano to geological scales. Here we suggest that trapped cold ions in an optical lattice can also be of help in understanding stick-slip friction, and also the way friction changes when one of the sliders undergoes structural transitions. For that scope, we simulated the dynamical properties of a 101-ions chain, driven to slide back and forth by a slowly oscillating electric field in an incommensurate periodic "corrugation" potential of increasing magnitude U0. We found the chain sliding to switch, as U0 increases and before the Aubry transition, from a smooth-sliding regime with low dissipation to a stick-slip regime with high dissipation. In the stick-slip regime the onset of overall sliding is preceded by precursor events consisting of partial slips of few ions only, leading to partial depinning of the chain, a nutshell remnant of precursor events at the onset of motion also observed in macroscopic sliders. Seeking to identify the possible effects on friction of a structural transition, we reduced the trapping potential aspect ratio until the ion chain shape turned from linear to zigzag. Dynamic friction was found to rise at the transition, reflecting the opening of newer dissipation channels.