High-power, pulsed-microwave measurements of critical currents in thin films of Y-Ba-Cu-O and Nb

The microwave (16.5-GHz) surface resistance of superconducting Y-Ba-Cu-O and Nb thin films is observed to increase with increasing applied microwave power. At higher powers, Nb films have been driven normal. These effects are attributed to high induced-current densities, approaching the critical values. From these measurements, values for the product Jc have been derived, and for Nb we have obtained the temperature dependence of this quantity. By using known values of, the values of Jc at microwave frequencies have been obtained. © 1991 The American Physical Society.