Non-Linear Microwave and Fast Optics Studies of YBCO Superconducting Films

During the period of this contract, the research program, "Non-linear microwave and fast optics studies of YBCO superconducting films" focused on several projects central to the program objectives. The main focus was on a collaborative study of the nonlinear microwave properties of superconducting YBCO, for which the research was carried out with collaborators at the Air Force Research Laboratory at Hanscom Air Force Base and the MIT Lincoln Laboratory. The research work included studies of; (1) the effect of the angular dependence of grain boundaries on the linear and non-linear microwave impedance of YBCO, (2) an extension of the coupled grain model to account for the distributed properties of junctions that are much longer than the London penetration depth, and have a distribution of the critical current densities and the normal state resistivities along the junction length, (3) second harmonic generation by Josephson junctions, (4) the effect of patterning on the surface impedance of YBCO thin films, and (5) the use of fast optics to investigate the basic interaction responsible for the high T(c) superconducting state in the BCS alkali metal-doped fullerene superconductors of K3C60 and Rb3C60. During this period one graduate student completed his M.S. thesis and three students completed Ph.D. theses.