Regensburg 2004 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 46: Poster
DY 46.83: Poster
Donnerstag, 11. März 2004, 16:00–18:00, Poster D
Smectic and crystalline order in colloidal monolayers on periodic one-dimensional substrate potentials — •Jörg Baumgartl1, Matthias Brunner2, and Clemens Bechinger1 — 12. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart — 2Fachbereich Physik, Universität Konstanz, 78457 Konstanz
There is growing interest in the phase behavior of two-dimensional (2D) colloids in the presence of one-dimensional (1D) periodic substrate potentials. The phase behavior of such systems is determined by two factors: (i) the relative orientation between the 2D crystal and the periodic potential troughs which selects a set of Bragg planes running parallel to the troughs and (ii) the commensurability ratio p=a′/d of the spacing a′ between these Bragg planes to the period d of the periodic potential. So far, only the phase behavior for p=1 was investigated and the following phases were observed for increasing (non zero) potential strength: modulated liquid and light-induced crystal. For other commensurability ratios additional, more complex phases are predicted.
We investigated experimentally the phase behavior for the case p=2 with the 1D periodic potential being created by two interfering laser beams. We observed for the first time the theoretically predicted intermediate phase between modulated liquid and light-induced crystal which is termed locked smectic. By analyzing the structure factor and the pair correlation function, this phase is characterized by liquid-like behavior along the potential troughs. In contrast to the modulated liquid the ordering perpendicular to the troughs is similar to the crystalline state, with particles occupying only each second trough.