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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 34: POSTERS Polymerphysics

CPP 34.14: Poster

Donnerstag, 28. Februar 2008, 17:00–19:30, Poster A

Direct observation of phonon decay in two-dimensional colloidal crystals — •Julian Dietrich¹, Jörg Baumgartl¹, Hans-Hennig von Grünberg², and Clemens Bechinger¹ — ¹2. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany — ²Institut für Chemie, Karl-Franzens-Universität, 8010 Graz, Austria

Lately there is growing interest in the band structures of so called phononic crystals which exhibit a phononic band gap. In a recent study it has been shown that such phononic band gaps can also be induced in colloidal crystals through anisotropic interactions including substrate-particle and particle pair interactions. In our experiment we investigate a new approach to determine the band structure of such a two-dimensional colloidal crystal directly from the phonon dynamics. Since colloidal suspensions are overdamped systems the phonons do not propagate but decay exponentially with a characteristic decay time inversely connected to the phonon band structure. We directly measure these decay times using video microscopy. Moreover, we apply a commensurate hexagonal substrate created with three interfering laser beams in order to tune the decay times. Finally, we investigate the behaviour of the decay times for vanishing substrate strengths; preliminary results indicate that hydrodynamical effects become important in the centre of the first Brillouin zone, i.e. for long wavelength phonons.