Figure 6. Thickness dependence of J_c for YBCO.

J_c(sf) for epitaxial YBCO films versus film thickness. (a) (Y_0.67Eu_0.33)Ba₂Cu₃O_7–δ at T=75.5 K, from Zhou et al.40 The solid curve is equation (12) with λ_c=620 nm. This value is too low and reflects increasingly non-uniform composition and microstructure across the thickness. (b) YBCO systems with a highly uniform through-thickness microstructure: Feldmann et al.42 (black data points and curve), with λ_ab(77)=339±5 nm and λ_c(77)=1,153±238 nm progressively thinned by ion milling; Zhou et al.43 (blue data points and curve) gives λ_ab(75.6)=253±4 nm and λ_c(75.6)=1,063±28 nm; Feldmann et al.44 (red data points and curve) gives λ_ab(75.6)=233±2 nm and λ_c(75.6)=1,980±790 nm.