Change of strength of vortex pinning in YBCO due to BaZrO_3 inclusions

N. Pompeo; V. Galluzzi; R. Rogai; G. Celentano; E. Silva

doi:10.1016/j.physc.2007.11.040

paper

Change of strength of vortex pinning in YBCO due to BaZrO_3 inclusions

arXiv:0710.3943 · doi:10.1016/j.physc.2007.11.040

Abstract

We probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7 GHz) on YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ films with and without sub-micrometer BaZrO $_{3}$ inclusions. We explore the temperature and field ranges 60 K $< T < T_{c}$ and 0 $< μ_{0} H <$ 0.8 T, with the field applied along the c-axis. The magnetic field induces a much smaller increase of the microwave resistivity, $Δ ρ_{1} (H) + i Δ ρ_{2} (H)$ , in YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ /BaZrO $_{3}$ with respect to pure YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ . $Δ ρ_{1} (H)$ is slightly superlinear in pure YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ (suggesting a possible contribution of thermal activation), but linear or sublinear in YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ /BaZrO $_{3}$ (suggesting a possible suppression of thermal activation as a consequence of BaZrO $_{3}$ inclusions). These features persist up to close to $T_{c}$ . We discuss our data in terms of the ratio $r = Δ X_{s}^{'} (H) /Δ R_{s}^{'} (H)$ in the framework of the models for the microwave surface impedance in the mixed state. Large $r$ are found in YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ /BaZrO $_{3}$ , with little field dependence. By contrast, smaller values and stronger field dependences are found in pure YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ . We discuss the different field dependence of the pinning constant.

4 pages, pdfTeX, presented at VORTEX Conference, to appear on Physica C