Stabilizing a two-dimensional colloidal solid by light-induced substrates: pinning, depinningand the effect of disorder

Abstract

We present Monte Carlo simulations of two-dimensional colloidal solidsinteracting with disordered and ordered substrate potentials whichin practice are created by interfering laser beams. The filling factorη, the number of colloids per potential minimum of the substrate, is taken to be either 1 or1/9. For an ordered and commensurate two-dimensional substrate withη = 1, the solid, being pinned to the periodicity of the substrate, always adopts the perfectorder of the substrate, irrespective of the strength of the pinning potential. Forη = 1/9, a solid phase (‘floating-solid’) with the same translational order decay characteristic asthe free solid can form. We explore the nature of this phase and show phase-diagramscontaining all three transitions: liquid to pinned-solid, liquid to floating-solid and floating-solidto pinned-solid. We also consider the case of a disordered substrate with a filling factorη = 1/9 and show that a floating-solid phase can also exist above such a glassy substrate.