Locked-Floating-Solid to Locked-Smectic Transition in Colloidal Systems

We investigate two-dimensional melting of a colloidal system in the presence of a one-dimensional periodic substrate potential created by two interfering laser beams. We study the commensurability ratio $p=\sqrt{3}a/2d=2$ with a the mean particle distance and d the period of the periodic potential. In contrast with the previously investigated case $p=1$, here we observe that melting of the locked-floating solid occurs via a novel locked-smectic phase, predicted by recent theoretical studies.

Figure 1

Averaged particle density $\rho$(x,y) and pair correlation function g(x,y) for (a, b) LFS, (c, d) LSm and (e, f) ML phase.

Figure 2

Pair correlation functions g(y) along the potential troughs for (a) LFS, (b) LSm, and (c) the ML phase. The data are displaced in vertical direction for clarity. The solid and dashed lines are fitting functions as explained in the text.

Figure 3

Mean square displacements of the particle motion (a) along and (b) perpendicular to the interference fringes for LFS (□), LSm (Δ) and the ML (○) phase. The solid lines correspond to fits which allow to extract the short-time and long-time diffusion coefficients.