Rf properties of high-T/sub c/ superconductors

The authors have investigated the rf properties of high-T/sub c/ superconductors over a wide range of temperature, frequency, and rf field amplitude. They have tested both bulk polycrystalline samples and thick films on silver substrates. At 150 MHz and 4.2 K, the authors have measured a surface resistance of 18 μΩ at low rf field and 3.6 mΩ at an rf field of 270 gauss. All samples showed a strong dependence of the surface resistance on rf field; however, no breakdown of the superconducting state has been observed up to the highest field achieved (320 gauss)