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 {lambda}{ital J}{sub {ital c}} have been derived, and for Nb we have obtained the temperature dependence of this quantity. By using known values of {lambda}, the values of {ital J}{sub {ital c}} at microwave frequencies have been obtained.