Spectrum of low-energy dipolar states in hydrated vitreous silica

The authors have extended to lower temperatures and frequencies, a recent dielectric study of hydroxyl doped vitreous silica. At given frequency the dielectric constant has a minimum at a temperature proportional to f1/3 while at given temperature the loss angle has a maximum proportional to T0.28 at a frequency proportional to T3. The behaviour is attributed to a distribution of dipolar two-level systems having tunnel splittings comparable to the thermal energies kT of the experiments and relaxation rates comparable to the experimental frequencies.