Kinks and nanofriction: Structural phases in few-atom chains

Dorian A Gangloff,Alexei Bylinskii,Vladan Vuletić

doi:10.1103/physrevresearch.2.013380

Dorian A Gangloff, Alexei Bylinskii + Show 1 more

Open Access

https://doi.org/10.1103/physrevresearch.2.013380

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Abstract

The frictional dynamics of interacting surfaces under forced translation are critically dependent on lattice commensurability. Performing experiments in a trapped-ion friction emulator, we observe two distinct structural and frictional phases: a commensurate high-friction phase where the ions stick-slip simultaneously over the lattice, and an incommensurate low-friction phase where the propagation of a kink breaks that simultaneity. We experimentally track the kink's propagation with atom-by-atom and sub-lattice site resolution, and show that its velocity increases with commensurability. Our results elucidate the commensurate-incommensurate transition and the connection between the appearance of kinks and the reduction of friction in a finite system, with important consequences for controlling friction at nanocontacts.

Highlights

Commensurability at the interface between two atomically smooth, elastic surfaces can fundamentally alter the energetic cost of their forced relative motion [1,2]
At sufficient mismatch between the two surface lattices, the interface develops defects distributed over a collection of atoms—kink solitons—that result in an incommensurate phase with smoother surface translation, reduced energy barriers, and reduced friction [4]
Two-dimensional versions of the C-I transition were observed at the interface between krypton monolayers and graphite [9], and between graphene and hexagonal boron nitride [10]

Summary

INTRODUCTION

Commensurability at the interface between two atomically smooth, elastic surfaces can fundamentally alter the energetic cost of their forced relative motion [1,2]. Friction emulators with synthetic interfaces consisting of colloidal particles [16] or cold trapped ions [17] have improved our understanding of fundamental surface science, owing to in-situ tuning of fundamental parameters, and to the ability to image individual particles. Such emulators [18,19,20] have been used to observe the Aubry transition [21,22,23] and kink transport [16,24]. In our finite onedimensional system, a kink is a metastable configuration of the atoms [4,36,37]—it has a higher energy than the global minimum with respect to translation—that is manifested in our experimental signal by atoms slipping at different times

NANOFRICTION EMULATOR

STRUCTURAL PHASES

TRAVELING KINK

SUMMARY AND OUTLOOK