Active microwave noise spectroscopy for characterization of superconducting materials

Most superconducting materials under dc current bias emanate excess noise which may extend from low frequencies up to the Tera-Hertz region. The microwave noise in some granular high Tc films at 12 GHz can be as high as 10 pW in 100 MHz bandwidth [1]. We studied these noises in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films grown on different substrates in the temperature range from 4.2 to 100 K using current bias and magnetic field as experimental variables. Analysis of the measurements provides valuable information on the superconductor crystalline microstructure, parameters of the intrinsic Josephson clusters, synchronization of the radiation from clusters and on the properties of the intergranular inclusions. Some of these information is difficult or even impossible to obtain by other methods.