Microwave impedance of YBa2Cu3O7-δ high-temperature superconductor films in a magnetic field

The temperature. field, and intensity (amplitude) dependences of the surface impedance of magnetron-sputtered YBa2Cu3O7-delta quasi-single-crystal films on a sapphire substrate with a CeO2 buffer layer were measured. The measurements were performed with a coplanar resonator at 5.25 GHz in a weak constant magnetic field 0<B<12 mT in the temperature range 13 K <T <80 K. They made it possible to obtain the surface resistance and penetration depth versus the temperature and the magnetic field strength and to determine the Contribution of Abrikosov vortices to the impedance. The cases with a frozen magnetic field and zero-field cooling with the field subsequently switched oil at temperatures below the critical value Were investigated separately. A substantial difference in the behavior of the high-frequency response of the vortices in these two cases was found. The Coffey-Clem and Brandt theories were used to Study the linear response and the critical state model the nonlinear response of the vortices. (C) 2005 American Institute of Physics.