Engineering nanocolumnar defect configurations for optimized vortex pinning in high temperature superconducting nanocomposite wires

We report microstructural design via control of BaZrO 3 (BZO) defect density in high temperature superconducting (HTS) wires based on epitaxial YBa₂Cu₃O₇-δ (YBCO) films to achieve the highest critical current density, J_c, at different fields, H. We find the occurrence of J_c (H) cross-over between the films with 1-4 vol% BZO, indicating that optimal BZO doping is strongly field-dependent. The matching fields, B φ, estimated by the number density of BZO nanocolumns are matched to the field ranges for which 1-4 vol% BZO-doped films exhibit the highest J_c (H). With incorporation of BZO defects with the controlled density, we fabricate 4-μm-thick single layer, YBCO + BZO nanocomposite film having the critical current (I_c) of ∼1000 A cm^-1 at 77 K, self-field and the record minimum I c, I_c (min), of 455 A cm^-1 at 65 K and 3 T for all field angles. This I_c (min) is the largest value ever reported from HTS films fabricated on metallic templates.