Regensburg 2004 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 51: Polymers and Colloids
DY 51.4: Vortrag
Freitag, 12. März 2004, 11:30–11:45, H3
Phase behavior of a 2D colloidal system on a triangular lattice — •Andreja Sarlah1, Thomas Franosch1, and Erwin Frey1,2 — 1Hahn-Meitner-Institut, Glienicker Straße 100, D-14109 Berlin, Germany — 2Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
We studied the phase behavior in 2D colloidal systems under the influence of an external periodic potential created by the interference pattern of laser beams forming a triangular lattice. In the special case, where the numbers of colloidal particles and of potential minima are commensurate, an integer number of particles gathers in each potential minimum. The colloidal particles within a single potential minimum form a composite object whose effective degrees of freedom are a few discrete orientational states. Upon increasing the strength of the external potential, first the composite objects orient, however, above some higher critical value, the long-range orientational order is lost. In particular, we are interested in systems with composite objects of 2 or 3 colloidal particles, i.e., dimers or trimers, respectively. In these systems, the orientational ordering provides a realization of 2D discrete spin models. The case of trimers can be mapped to the spin-1/2 Ising model whereas the system of dimers is mapped to a spin model characterized by several independent control parameters leading to a richer phase diagram. Our theoretical results are in good agreement with the recently reported experimental results. We predict that by varying the strength of the screened interaction among colloidal particles at least a part of the phase diagram of a spin model for dimers should be accessible by experimental studies.