8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.126Wed 711:10-14:00Interactions between geometric defects in 2D colloidalsystemsDavid Polster, 1 Georg Maret, 1 and Peter Keim 11 Universität Konstanz, Universitätsstrasse 10, 78464, Konstanz, GermanyMelting in 2D, according to the Kosterlitz-Thouless-Halperin-Nelson-Young theory, involves theformation and dissociation of topological defect pairs. Because these defects distort the hexagonalsymmetry of the 2D crystal the formation of an isolated topological point defect is not possible.Consequently, topological defects occur always as dislocation or disclination pairs. Geometricdefects on the other hand are isolated point defects which can be experimentally created e. g. withan optical tweezer. While topological defects appear already near k B T geometric defects need alot more energy to create. We study the interactions of geometric defects with other defects or thesurrounding undisturbed lattice in a 2D system of paramagnetic colloidal particles sedimented toa water/air-interface. By applying a magnetic field the particles form a 2D crystal with hexagonalsymmetry which can be manipulated with an optical tweezer. We will show the formation ofdifferent configurations of monovacancies and their diffusion as well as the arrangement of multivacanciesand their diffusion. We compare our results to recent simulations by Lechner et al. [1-3]and find most but not all of the configurations predicted there. This can be explained by the factthat we use a system with dipole interactions while Lechner et al. simulate a Gaussian core system.[1] W. Lechner, E. Schöll-Paschinger, C. Dellago, Journal of Physics: Condensed Matter20, 404202 (2008).[2] W. Lechner, C. Dellago, Soft Matter 5, 646 (2009).[3] W. Lechner, C. Dellago, Soft Matter 5, 2752 (2009).126