Regensburg 2010 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 26: Poster Session

MM 26.46: Poster

Dienstag, 23. März 2010, 14:45–16:30, Poster C

Phase transitions of colloidal monolayers on decagonal light induced substrates — Günther Gera, •Thomas Bohlein, Jules Mikhael, and Clemens Bechinger — 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany

Two dimensional phase transitions remain of high interest to a broad scientific community. According to KTHNY theory, melting in 2D occurs via two sequential defect-driven phase transitions. In this context colloidal systems, having a multitude of accessible interactions, offer a suitable way to investigate such phenomena in real space. Most of the work considered 2D colloidal systems with only mutual interactions, or in few cases interaction with underlying periodic substrate potentials. Here we report measurements of the complex phase behavior of a triangular colloidal monolayer in the presence of a quasiperiodic substrate potential acting via optical forces on the particles. Experimentally, it is created by interfering 5 laser beams. This potential, although not periodic, has a long range order and a decagonal rotational symmetry. At different potential strengths several phenomena are depicted. At low laser intensities, reorientation of the high symmetry axis of the crystal is observed. For higher intensities, we identify the typical geometrical point defects which mediate the transition to the quasicrystalline phase. Here, the structure factor exhibits the decagonal symmetry as expected. For certain densities, line defects lead to a transition to the Archimedean-like tiling phase.