Microwave and superconducting techniques for measurements on unconventional Josephson junctions

[摘要] The frst part of the thesis describes the instrumentation, testing and analysis of a planar circuit designed for the measurement of the current-phase relationship of niobium-cobalt-insulator-niobium Josephson junctions. A detailed analysis method and fitting routine was developed but the results show that an irreducible mutual inductance places a limit on the accuracy of the chip for the intended measurement. The second part describes a study of the magnetic and microwave properties of a range of thin film niobium coplanar resonators with cobalt and normal metal layers. Magnetic measurements show a magnetic dead layer of 1.3 nm. The observed microwave losses are found to be two orders of magnitude higher than for high quality niobium films. Computer simulation shows that this is mainly due to conductive, rather than magnetic losses, and is in good agreement with the observed proportionality to cobalt thickness. Measurements of the temperature and magnetic field dependence of the losses and resonant frequency as a function of the cobalt thickness show no signs of the oscillatory thickness dependence reported in a number of other experiments. The temperature dependence of all films is found to be in good agreement with Mattis-Bardeen theory.

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics