Anomalous microwave response of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// granular thin films under magnetic fields

The microwave response of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) granular films has been studied at a microwave frequency of 30.5 GHz. In absence of a magnetic field, the dependencies of a normal microwave response on the bias current was observed at a temperature close to T/sub c/. When a magnetic field ranging from 5.0 to 33.0 mT is applied, the responses broaden and shift toward a lower temperature. In the superconducting state, the responses were found to be highly dependent on the magnetic field. For a current of 5.0 mA and a magnetic field above 17.0 mT, the responses increased and did not vanish, even at a very low temperature, which is believed to be correlative with the anisotropic character of the structure.