Dielectric Loss Measurements Below 15 Kelvin by using Superconducting Microwave Resonators

The paper deals with the theoretical and practical investigation of superconducting Nb3 Sn-helical-resonators with quality factors greater than 108 which allow the determination of dielectric loss tangents in the range of 0.1 to 10GHz and below 15KHz with an absolute accuracy of 10-7. The cryogenic loss of various polymers is found to be considerably smaller than the room temperature data, its pronounced temperature and frequency dependence is qualitatively explained by tunneling relaxation as well as the low frequency tail of the infrared absorption, both mechanisms being enhanced by dipolarity and irregularity of the molecular structure.