Microwave surface resistance of epitaxial YBa2Cu3O7 thin films on sapphire

Microwave surface resistance data were measured on pairs of YBa2Cu3O7 thin films on Al2O3 {1102} substrates by a parallel plate resonator technique. The surface resistance Rs at 10 GHz was 65 μΩ at 10 K and 850 μΩ at 77 K. These epitaxial YBa2Cu3O7 films were grown on 500-A-thick buffer layers of SrTiO3. X-ray diffraction data showed that the YBCO thin films with the SrTiO3 buffer layers have better in-plane epitaxy than those without such buffer layers. Critical current density of 2x106 A/cm2 at 74 K was measured by the ac mutual inductance response of the films. The improved microwave surface resistance and the higher critical current density are believed to be the results of better in-plane epitaxy