Study of the Usual and the Unusual Effect of a DC Magnetic Field on the Microwave Properties of Different Superconducting YBCO Thin Films

Abstract

An experimental observation of the improvement of the microwave properties of high temperature superconductor thin film subjected to a weak DC magnetic field is reported. This characterization was done with two YBCO films deposited onto LaAlO3 substrates and the coplanar resonator technique was used to extract their microwave properties. The results are presented as a comparison between the behaviors of a sample that exhibits an unusual effect with another sample that has a usual behavior. To understand the origins of such a difference, the crystallographic properties and the microstructure were investigated respectively by mean of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). A major difference in terms of growth axis orientation and of granularity has been observed between the two samples. Based on the correlated variation of the surface resistance and the surface reactance of the considered sample, the presence of anomalous weak links and also of a-axis grains in one of the films could explain its unusual behavior.