Change of strength of vortex pinning in YBCO due to BaZrO3 inclusions

• Published in: Physica. C, Superconductivity Vol. 468; no. 7-10; pp. 745 - 748
• Main Authors: Pompeo, N., Galluzzi, V., Rogai, R., Celentano, G., Silva, E.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01-04-2008; Elsevier Science
• Subjects: BaZrO3 inclusions; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cuprates superconductors (high tc and insulating parent compounds); Exact sciences and technology; Physics; Pinning; Properties of type I and type II superconductors; Superconductivity; Surface impedance; Vortex lattices ,flux pinning, flux creep; YBa2Cu3O7−δ; 74.25.Qt; Surface impedance; BaZrO3 inclusions; Pinning; 74.72.Bk; YBa2Cu3O7−δ; 74.25.Nf; YBa2Cu3O7-δ; Barium Zirconates; Inorganic compounds; Electrical conductivity; Mixed state; Microwave radiation; Transition element compounds; Magnetic field effects; Inclusions; Flux pinning; Microwave conductivity; High-Tc superconductors; High frequency; Activation energy; Barium Copper Yttrium Oxides Mixed
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2007.11.040

We probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7GHz) on YBa2Cu3O7−δ films with and without sub-micrometer BaZrO3 inclusions. We explore the temperature and field ranges 60 K <T<Tc and 0<μ0H<0.8T, with the field applied along the c-axis. The magnetic field induces a much smaller increase of the microwave resistivity, Δρ1(H)+iΔρ2(H), in YBa2Cu3O7−δ/BaZrO3 with respect to pure YBa2Cu3O7−δ. Δρ1(H) is slightly superlinear in pure YBa2Cu3O7−δ (suggesting a possible contribution of thermal activation), but linear or sublinear in YBa2Cu3O7−δ/BaZrO3 (suggesting a possible suppression of thermal activation as a consequence of BaZrO3 inclusions). These features persist up to close to Tc. We discuss our data in terms of the ratio r=Δρ2(H)/Δρ1(H) in the framework of the models for the microwave surface impedance in the mixed state. Large r are found in YBa2Cu3O7−δ/BaZrO3, with little field dependence. By contrast, smaller values and stronger field dependences are found in pure YBa2Cu3O7−δ. We discuss the different field dependence of the pinning constant.