File:Bachelorthesis Homann 2015.pdf

The low temperature properties of amorphous solids are governed by tunneling systems. The phenomenological standard tunneling model gives a qualitively good description of those properties. In earlier dielectric measurements, however, considerable deviations from this model were observed. The aim of this thesis was to gain experimental insights into the behaviour of a well-known glass in the range of MHz as previous investigations focused on lower or higher frequencies. In the frame of this thesis, the dielectric properties of the bor-crown glass N-BK7 were examined in the temperature range between 8 mK and 300 K. The measurements were carried out with a parallel LC circuit. The glass served as a dielectric of the capacitor. The resonance frequency amounted to approximately 30 MHz. The characteristic minimum of the real part of the dielectric permittivity is found at a temperature of 2.21 K for N-BK7. Its position follows the frequency dependence predicted by the standard tunneling model. The ratio of the slopes below and above the minimum is determined to be -2:7. The dielectric loss exhibits an absorption maximum at 6 K. Comparing the experimental data with numerical calculations, significant deviations from the standard tunneling model become visible. For temperatures below 100 mK the dielectric properties depend on the transmission power.