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The effect of BaZrO3 (BZO) dopant concentration on superconducting properties in YBa2Cu3O6+x thin films is investigated in a wide magnetic field range up to 30 T. Based on the magnetization and resistivity measurements, the optimal BZO concentration for flux pinning is found to be 4% up to 20 T and increasing up to around 8% in higher fields. This result is qualitatively explained by a model where more BZO is needed in order to organize optimal columnar defect structure at high fields because the amount of single BZO particles acting as isotropic point pinning centers is increased, especially in high BZO concentrations. This means that for applications of thin film or coated conductor structures carried out at high magnetic fields, even higher dopant concentration than used in a low-field range should be produced in order to attain the optimal flux pinning conditions. [ABSTRACT FROM AUTHOR]

The high anisotropy of the critical current density in the high-temperature superconductor YBa2Cu3O6+x can be compensated by changing the pinning landscape, for example, through doping with BaZrO3. We measure the change due to BaZrO3 doping in the effective electron mass anisotropy, γ, by resistive measurements of the upper critical field in pulsed high magnetic fields. It is found that the angular dependence of the upper critical field follows the Blatter scaling up to 30 T but the irreversibility field does not. We also report a significant reduction in the effective electron mass anisotropy from 6.0 to 3.4 by BaZrO3 doping. [ABSTRACT FROM AUTHOR]