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Study of symmetries in colloidal monolayers

Nature likes some symmetries, but dislikes others. Ordered solids often display a so-called 6-fold rotation symmetry. To achieve this kind of symmetry, the atoms in a plane surround themselves with six neighbours in an arrangement similar to that found in a honeycomb. As opposed to this, ordered materials with 7-fold, 9-fold or 11-fold symmetries do not appear to arise in nature.

Researchers from the Max Planck Institute for Metals Research, the University of Stuttgart and the Technische Universität Berlin discovered the reason for this when they tried to impose a 7-fold symmetry on a layer of charged colloid particles using strong laser fields: the emergence of ordered structures requires the presence of nuclei to which the atoms with the corresponding symmetry can attach. Such nuclei can be found in large numbers in the symmetries for which nature shows a preference. However, they only arise sporadically in patterns with 7-fold symmetry.

symmetries in monolayer colloids

The researchers generate light patterns like the ones shown in the picture above by superimposing several laser beams (Image: Jules Mikhael, University of Stuttgart). Flower-shaped structures form in the laser reliefs which act as a nucleus for the order (top left: 5-fold; top right: 6-fold; bottom left: 7-fold; bottom right: 8-fold).

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