Measurement of Vortex Pinning in YBCO and YBCO/BZO Coated Conductors Using a Microwave Technique

In order to study the effect of pinning in coated conductors, we have used pulsed laser ablation to grow YBa2Cu3O7-x (YBCO) and YBa2Cu3O7-x/BaZrO3 (YBCO/BZO) films on metallic templates. Despite the complexity of the structure, after the optimization of the deposition procedure, the YBCO/BZO showed only a moderate reduction of Tc with respect to the pure YBCO sample. We use a very high frequency (∼47.7 GHz) dielectric resonator technique in order to induce very short distance vortex shaking, thus probing the steepness of the potential well. We report on measurements of the microwave response of the superconducting structures in terms of the quality factor Q and the frequency resonance ν0 as a function of a moderate dc magnetic field H, at different temperatures T. To keep as much contact as possible to the raw data (Q and ν0), in agreement with a generalized model for vortex dynamics, we determine the pinning parameter r and the upper limit for the creep factor χM. Based on the field dependence of the pinning parameters, the vortex pinning regimes were discussed. We find that the improvement of pinning by BZO is much reduced with respect to the effect observed in films grown on single crystals. In particular, the reduction of the critical temperature must be taken into account in order to appreciate the results.