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

Wed 711:10-14:00P5.85Fluctuation dominated crystallization in a quenched 2DsystemPeter Keim, 1 Patrick Dillmann, 1 and Georg Maret 11 Universität Konstanz, Universitätsstr. 10, 78457, Konstanz, GermanyThe melting process in a two-dimensional system in equilibrium has been a matter of debate forlong. While Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY-Theory) proposed twocontinuous transition from the crystalline to the isotropic fluid phase with an intermediate hexaticphase [1-3], Chui argued for a first order transition for freezing mediated by the spontaneousgeneration of grain boundaries [4], similar to the case in three dimensional systems. With ourexperiment of super-paramagnetic colloidal particles confined by gravity to an absolutely flat liquid/airinterface forming a 2D monolayer we were able to show that KTHNY-Theory holds forboth, freezing and melting if the system is always in thermal equilibrium [5]. If the system iscooled down rapidly from the fluid to the crystalline state the solidification differs drastically fromthe equilibrium melting and freezing scenario [6]. There is no indication of the presence of thehexatic phase. The system solidifies to a poly-crystalline structures with lots of small grains ofdifferent orientation – but our findings do not go along with critical nucleation theory [7]. For allgiven sizes, grains are always more likely to shrink and their lifetime is comparable to precriticalnuclei in the isotropic fluid phase. The local order fluctuates strongly until some grains touch andfluctuations are suppressed. For the early stage after the quench, growth exponents and fractaldimensions of the grains are given in this presentation.[1] J. M. Kosterlitz, D. J. Thouless, J. Phys. C, 6, 1181 (1973)[2] B. I. Halperin, D. R. Nelson, Phys. Rev. Lett. , 41, 121 (1978) [3] A. P. Young, Phys. Rev. B,19, 1855 (1979)[4] S. Chui, Phys. Rev. B, 28, 178 (1983)[5] P. Keim, G. Maret, H. H. von Grünberg, Phys. Rev. E 75, 031402 (2007)[6] P. Dillmann, G. Maret, P. Keim, Jour. Phys. Cond. Matt. 20, 404216 (2008)[7] S. Auer, D. Frenkel, Nature, 409, 1020 (2001)85