Particle excursions in colloidal crystals

have performed synchrotron small-angle x-ray diffraction experiments on cha rge-stabilized colloidal crystals. The mean squared displacements, obtained from Debye-Waller factors, decrease with increasing density beyond freezin g. Irrespective of the range of the repulsion, our data and previous result s lie on a common curve, linearly scaled between the melting and close-pack ed densities. Surprisingly, the excursions are smaller than predicted by th eory.