Doping dependences of superconducting gap parameters. (a) Nodal gap energy 2ΔN (blue circles) and antinodal gap energy 2Δ∗ (red squares) . The solid curve denotes an energy of 8.5kBTc. (b) Square of nodal-to-antinodal gap ratio (ΔN/Δ∗)2 determined from ARPES . (c) Superfluid density ρs determined from magnetic penetration depth (triangles)  and from heat capacity (crosses) . (d) Superconducting gap profiles normalized to the antinodal gap for underdoped and optimally doped samples with Tc = 42, 66, and 91 K (UD42, UD66, and OP91, respectively). (e) Correlation between 2ΔN/kBTc and 2Δ∗/kBTc ratios. The insets illustrate the occurrence of incoherent electron pairs in strong coupling superconductivity.
Ino et al. Nanoscale Research Letters 2013 8:515 doi:10.1186/1556-276X-8-515