Structural characterization and microwave loss of Nd_1.85Ce _0.15CuO_4-y superconducting thin films on yttria-stabilized zirconia buffered sapphire

We have grown superconducting Nd_1.85Ce_0.15CuO _4-y (NCCO) thin films on (11̄02) sapphire using a yttria-stabilized zirconia (YSZ) buffer layer, which has been demonstrated to be the best material for the growth of n-type superconducting NCCO thin films. The films are c-axis oriented, epitaxially grown with a small mosaic spread of 0.2°and a Rutherford backscattering spectroscopy channeling yield of ∼9%. Cross-sectional transmission electron microscopy images reveal a sharp interface between NCCO and YSZ. The microwave surface resistance of NCCO films on YSZ buffered sapphire at 9.6 GHz is only 80 μΩ at 4.2 K in zero magnetic field, which is comparable to Y₁Ba₂Cu ₃O_7-y films at similar reduced temperature, as a consequence of the decrease of structural imperfection in the film. The temperature dependence of the surface resistance and magnetic penetration depth in these films further confirms the s-wave BCS nature of NCCO.