Figure 2: Field dependence of the pairing strength extracted from H_c2.

(a) λ(H) for the three crystallographic directions. The inset shows the calculated H_c2 curves using the strong coupling model, each with a fixed coupling constant λ from 0.4 up to 0.7 in steps of 0.02 from left to right, together with the data of Fig. 1a. (b) zoom of the inset of a for H//c. The H_c2 lines are almost vertical, visualizing the negligible role of the orbital limitation in the determination of H_c2 for this field direction.