Figure 3. Low-temperature fits: gap symmetry.

(a) The low-T fit to λ(T) data determined from our measurements of J_c(sf) for YBa₂Cu₃O₇ using equation (7). The fit yields λ=128.3 nm and Δ₀=16.6 meV. The red crosses show the low-T penetration depth measurements of Hardy et al.20 for comparison. (b) The low-T fit to λ(T) for NbN using equation (6) to determine Δ₀. The characteristic flat T-dependence of s-wave superconductors at low T is evident. The fits yield λ=189 nm and Δ₀=2.95 meV.