Figure 2. Summary comparison of calculated and measured values.

(a) Comparison of calculated thin-film self-field J_c0 values with measured J_c0 values. J_c0 is calculated from reported λ values using equations (3) and (4). Red data points are type-I superconductors, black data points are type II. The blue arrow for YNi₂B₂C shows the effect of the correction factor (λ/b)tanh(b/λ), discussed in the text, when b>λ. Error bars reflect the range of reported λ₀ values—see Supplementary Table 1. The sample annotation follows the vertical order of the data points. (b) λ₀ values calculated from reported J_c(T) data and plotted versus independently measured λ₀ values. The magenta arrow and symbols show the effect of improvement over time in self-field J_c for six films of MgB₂. The data terminates on the dashed line where J_c is now fundamentally limited by the superfluid density. Comparative data for YBCO over time is shown in Supplementary Figure 4. (c) Summary of values of Δ₀ calculated from the low-T behaviour of λ(T) using equations (6) and (7), plotted versus measured values of Δ₀.