Fluctuation-induced order in two-dimensional colloidal clusters

Abstract

The behaviour of a finite number (N = 29) of paramagnetic colloidal particles in 2D circular hard-wall cavities is investigated. By applying a magnetic field B, the interaction between the particles is varied. We demonstrate that the angular diffusion of the particles which are arranged in shells is highly anisotropic and shows a non-monotonic behaviour as a function of B. When reducing radial particle fluctuations in one shell by a ring-shaped optical tweezer, the relative angular diffusion between adjacent shells increases again. This clearly demonstrates that radial particle fluctuations are responsible for an enhanced registration between adjacent shells.