Superlubricpinned transition in sliding incommensurate colloidal monolayers
Abstract
Twodimensional (2D) crystalline colloidal monolayers sliding over a laserinduced optical lattice providing the periodic "corrugation" potential recently emerged as a new tool for the study of friction between ideal crystal surfaces. Here, we focus in particular on static friction, the minimal sliding force necessary to depin one lattice from the other. If the colloid and the optical lattices are mutually commensurate, the colloid sliding is always pinned by static friction; however, when they are incommensurate, the presence or absence of pinning can be expected to depend upon the system parameters, like in onedimensional (1D) systems. If a 2D analogy to the mathematically established Aubry transition of onedimensional systems were to hold, an increasing periodic corrugation strength U_{0} should turn an initially freesliding, superlubric colloid into a pinned state, where the static friction force goes from zero to finite through a welldefined dynamical phase transition. We address this problem by the simulated sliding of a realistic model 2D colloidal lattice, confirming the existence of a clear and sharp superlubricpinned transition for increasing corrugation strength. Unlike the 1D Aubry transition, which is continuous, the 2D transition exhibits a definite firstorder character, with a jump of static friction. With no change of symmetry, the transition entails a structural character, with a sudden increase of the colloidcolloid interaction energy, accompanied by a compensating downward jump of the colloidcorrugation energy. The transition value for the corrugation amplitude U_{0} depends upon the misalignment angle θ between the optical and the colloidal lattices, superlubricity surviving until larger corrugations for angles away from the energetically favored orientation, which is itself generally slightly misaligned, as shown in recent work. The observability of the superlubricpinned colloid transition is proposed and discussed.
 Publication:

Physical Review B
 Pub Date:
 October 2015
 DOI:
 10.1103/PhysRevB.92.134306
 arXiv:
 arXiv:1508.00147
 Bibcode:
 2015PhRvB..92m4306M
 Keywords:

 68.35.Af;
 64.70.Nd;
 83.85.Vb;
 82.70.Dd;
 Atomic scale friction;
 Structural transitions in nanoscale materials;
 Small amplitude oscillatory shear;
 Colloids;
 Condensed Matter  Mesoscale and Nanoscale Physics;
 Condensed Matter  Soft Condensed Matter
 EPrint:
 9 pages, 10 figures