POWER AND MAGNETIC FIELD-INDUCED MICROWAVE-ABSORPTION IN TL-BASED HIGH-TC SUPERCONDUCTING FILMS

The increase in the microwave surface resistance R(s) of high T(c) superconductors at elevated microwave power levels is reported for both oriented and unoriented T1-based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in R(s) and in the surface reactance X(s). The increase in R(s) with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in R(s) with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.