Polarizability of the low frequency excitations in disordered solids. [Polymethylmethacrylate]

An attempt to find manifestations of an electric dipole moment associated with the low-temperature thermal properties of glasses has enabled the setting of very low limits for GeO/sub 2/ and PMMA, 0.06 and 0.16 Debye respectively. Measurements of the temperature dependence of the dielectric constant and the electric field dependence of the thermal conductivity of SiO/sub 2/ in conjunction with dielectric measurements by Schickfus et al. has pinned down some of the features of a tunneling systems model. The potentials must be nearly symmetric (..delta../sub 0/>> ..delta../sub A/) and the distribution of these states, n(..delta..)/sub tun/, must be considerably more uniform than one would calculate from measurements of the specific heat of SiO/sub 2/, n(..delta..)/sub C/sub p/. (auth