Experiments on the structure and vibrations of fractal solids

Measurements performed on carefully prepared series of silica aerogels are reported. These materials were studied with small-angle neutron scattering, revealing a fractal structure that can extend up to at least two orders of magnitude in length. The corresponding collective vibrations were investigated by Brillouin, Raman, and inelastic neutron scattering. All results are consistently explained in terms of fractons.