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Sven Deutschländer: „Phase Transitions in 2D colloidal systems subject to substrate-induced random potentials ”
Universität Konstanz

We investigate the thermodynamics of two-dimensional colloidal systems with magnetic dipol-dipol interaction subject to substrate-induced random potentials. We are interested in the structure and dynamics of possible phases, in particular the effect of the strength and randomness of the external potential on the order and mechanism of phase transitions, transition temperatures and the emergence and conformation of grain boundaries. For long wavelength potentials and as long as the randomness of the potenial does not exceed a critical value, analytic theories predict phase transitions mediated by dissociation and recombination, respectively, of dislocation and disclination pairs, from the solid over an hexatic phase to an isotropic liquid [1-3]. We performed freezing of 2D colloidal systems on disordered substrates with repulsive potentials varying on slow and medium range and could show that the first occurrence of hexatic characteristics as well as the transition to a crystalline state are shifted to lower temperatures which is consistent with [1-3]. In addition, we observed the developing of phase equilibria indicating first order characteristics which also seem to be induced by the external potential.


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  2. M. Cha and H. Fertig, Physical Review Letters 74(24), 4867 (1995).
  3. D. Carpentier and P. Le Doussal, Physical Review Letters 81(9), 1881 (1998).