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

P5.44Wed 711:10-14:00Non-equilibrium phase transition in 2DPatrick Dillmann, 1 Georg Maret, 1 and Peter Keim 11 Universität Konstanz, Universitätsstra 10, 78457, Konstanz, GermanyWe use super-paramagnetic dipolar colloidal particles confined by gravitation to a flat water-airinterface as a model system to study the non-equilibrium liquid-solid phase transition in twodimensions. The system temperature is adjustable by changing the strength of an externalmagnetic field perpendicular to the water-air interface. Increasing the the magnetic field quenchesa liquid system to a strongly undercooled state on a timescale of ms which immediately inducesthe solidification of the system. Video microscopy provides exact time dependent positions ofup to 10000 particles simultaneously on all relevant length- and timescales [1]. To analyze thesolidification process we identify crystal-like structures which emerge after the quench with thehelp of several criteria reflecting the orientational and translational order of a hexagonal crystallattice. The magnitude and phase of the complex bond order parameter introduced by Nelsonand Halperin [2] enables us to localize regions with an adequate degree of orientational order.A criterion based on the Lindemann criterion in three dimensions is used to recognize areaswith a sufficient proportion of translational order. The combination of these criteria allows usa time-dependent determination of crystal-like structures. By tracking these structures in timewe are able to investigate the solidification in detail. First results shows that in this system thenon-equilibrium liquid-solid phase transition can not be describe in the framework of classicalnucleation theory.[1] F. Ebert, P. Dillmann, G. Maret, P. Keim, Rev. Sci. Instrum. 80, 083902 (2009).[2] D. R. Nelson and B. I. Halperin, Phys. Rev. B 19, 2457 (1979).44