File:Masterthesis Tsurkan 2017.pdf

The low temperature properties of glasses are defined by atomic tunneling systems. The standard tunneling model lays the groundwork for understanding the behavior of glasses, however it fails to account for some major characteristics of data recently obtained. Therefore two extensions to the model are considered in the framework of this thesis, namely spectral diffusion and the influence of nuclear electric quadrupole moments. By using two-pulse polarization echoes as a phase coherent method, tunneling systems were studied at 10 and 15 mK. Both N-KZFS11, containing 181Ta, and HY- 1, containing 165Ho, were measured at 0mT and 230 mT. Also, magnetic field sweeps were performed for both glass samples. Results showed no difference between the echo signal decay rates in the field and non-field experiment for N-KZFS11. Spectral diffusion model was fitted but was not able to completely describe the decay. Also, decay curves for non-field measurements for HY-1 were fitted with the spectral diffusion model showing good agreement. During a magnetic field sweep, a previously unseen demagnetization effect was observed in HY-1.