Berlin 2012 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 29: Posters II

DY 29.12: Poster

Thursday, March 29, 2012, 17:00–19:00, Poster A

Phase Transitions in 2D colloidal systems subject to substrate-induced random potentials — •Sven Deutschländer, Georg Maret, and Peter Keim — University of Konstanz, Department of Physics, 78457, Konstanz, Germany

We investigate the effect of substrate-induced random potentials on the thermodynamics of a two-dimensional colloidal system with magnetic dipol-dipol interaction. In particular, we are interested in the structure and dynamics of possible phases, the order and mechanism of the phase transitions, and transition temperatures as a function of strength and randomness of the external potential. We show that the first occurrence of hexatic characteristics as well as the transition to a crystalline state are, triggered by the substrate potential, shifted to lower temperatures which is in agreement with theories by D. Nelson, and M.-C. Cha and H. Fertig. Further, we found that, at finite randomness and low system temperatures, the system occupies a solid state. This verifies simulations by S. Herrera-Velarde and H. H. von Grünberg, as well as Cha and Fertig’s reconsiderations of Nelson’s theory. The latter postulates a re-entrance from the solid to the hexatic phase at low temperatures for arbitrary small randomness what is not seen in our experiment. In addition, we observe the developing of phase equilibria indicating first order characteristics which also seem to be induced by the external potential, and show that their range is dependent on the randomness.