Most systems in nature and technology are mixtures of differently sized particles. Each distinct particle size introduces another length scale and its competition gives rise to an exceedingly rich phenomenology in comparison with single-component systems. Already the simplest conceivable multi-component system, i.e. a binary mixture of hard spheres, exhibits interesting and complex behavior. It has been predicted that the dominant wavelength in such systems shows a marked jump as a function of the packing fraction of the two particle species. We experimentally observed this so-called structural crossover in a binary colloidal hard sphere system whose structure was investigated by means of confocal microscopy. In addition, our results show that structural-crossover is related to the lateral extension of networks containing only equally sized particles that are connected by nearest neighbor bonds.
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