Millimeter microwave properties of high-temperature superconductors. Ph.D. Thesis
The broad objective of this experimental study is to characterize the microwave properties of high temperature superconductors in the presence of strong magnetic fields. The dissertation primarily describes the development of a microwave system (35 GHz) that measures transmitted and reflected power fractions of thin superconducting films, and the analysis techniques used to interpret the results. YBa2Cu3O7-x (YBCO) films deposited on LaAlO3 substrates are investigated, with the microwave propagation direction and magnetic field both perpendicular to the film and parallel to the crystalline c axis. Results show no hysteresis or dependence on incident power level, and are changed markedly when power impinges on the substrate instead of the film. Two analysis approaches are implemented, both of which require the solution of the problem of wave propagation through a bilayer structure. Uniform axial propagation constants are assumed for each medium, as supported by numerical modelling. The first method employs Coffey-Clem theory for the electrodynamic response of the superconductor, focusing on losses due to vortex motion. A gradient line search of the multidimensional parameter space yields optimal theory parameters, which give good agreement with the data. The second method employs direct numerical inversion of the above mentioned wave solution via the two dimensional Newton-Raphson algorithm. Complete results are given for a YBCO film in terms of the complex penetration depth as a function of temperature and field (80-95K, 0-5.4 tesla), revealing substantial increases due to the applied field. Supplemental far-infrared transmission measurements for YBCO exhibit only minimal magnetic field effects relative to those anticipated, implying that the dominant dissipation processes are probably not the same as at microwave frequencies.
- Research Organization:
- Notre Dame Univ., IN (United States). Dept. of Aerospace and Mechanical Engineering
- OSTI ID:
- 236801
- Report Number(s):
- N-96-22245; NIPS-96-07610; TRN: 9622245
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
Similar Records
Upward curvature of the microwave surface resistance vs. field in YBCO films and the Clem`s Rs model
Effective microwave surface impedance of superconducting films in the mixed state