Role of transverse displacements for a quantized-velocity state of the lubricant

TL;DR

This paper demonstrates a quantized sliding state in a more realistic 2D model of a solid lubricant, showing how transverse displacements and kinks influence lubricant velocity and motion at finite temperatures.

Contribution

It extends the understanding of quantized lubricant sliding states from idealized 1D models to more realistic 2D Lennard-Jones systems, including effects of transverse displacements.

Findings

Quantized sliding state observed in 2D Lennard-Jones model.

Evidence of quantized sliding at finite temperature.

Backward motion due to anti-kinks demonstrated.

Abstract

Within the idealized scheme of a 1-dimensional Frenkel-Kontorova-like model, a special "quantized" sliding state was found for a solid lubricant confined between two periodic layers [PRL 97, 056101 (2006)]. This state, characterized by a nontrivial geometrically fixed ratio of the mean lubricant drift velocity <v_cm> and the externally imposed translational velocity v_ext, was understood as due to the kinks (or solitons), formed by the lubricant due to incommensuracy with one of the substrates, pinning to the other sliding substrate. A quantized sliding state of the same nature is demonstrated here for a substantially less idealized 2-dimensional model, where atoms are allowed to move perpendicularly to the sliding direction and interact via Lennard-Jones potentials. Clear evidence for quantized sliding at finite temperature is provided, even with a confined solid lubricant composed of multiple (up to 6) lubricant layers. Characteristic backward lubricant motion produced by the presence of "anti-kinks" is also shown in this more realistic context.