Electrical Polarizability of Phonon Scattering States in Glasses

Abstract

Tunneling states¹ in glasses should be electrically polarizable. Hence one might expect that the thermal conductivity would change in an electric field. In two previous studies, no effect was seen^2,3. In the first experiment, however, the dielectric polarizability of the glass was not known, and the sensitivity of the experiment was reduced because of the relatively high temperatures used, T > 2° K. In the second experiment, the experiment was performed at lower temperatures (T > 0.15°K), and the polarizability was measured. The latter, however, was found to be quite small, which again should decrease the sensitivity of the experiment. In the present experiment, we have chosen a glass of very high polarizability, and have also measured as low as 0.2° K. The experimental technique was the same as that used by Stephens³. The soda-silica glass sample had the composition 75 wt% SiO₂, 12 wt% Na₂O, with the remainder B₂O₃, K₂O, and Al₂O₃. The relative change in thermal conductivity, defined as Δ Λ/Λ = (Λ(E,T) - Λ (O,T) ) /Λ(O,T) in an applied field as high as 53 kV/cm, is shown in Fig. 1. As in the previous studies, no systematic change was detectable. In zero field, the thermal conductivity was found to scatter within the range indicated by the two curves in Fig. 1, arising mostly due to thermal drift.

Work supported by the National Science Foundation, Grant # DMR 78-01560