Figure 4: Doping dependences of gap parameters.
From: Relation between the nodal and antinodal gap and critical temperature in superconducting Bi2212
(a) Superconducting-gap energies scaled by Tc, plotted as functions of sin2θ, and vertically offset by 5 for each doping. Filled circles denote the BB gap determined with hν=8.5 eV. Open squares and diamonds denote the AB gap determined with hν=8.5 and 7.0 eV, respectively. Solid curves and dotted lines denote the next-higher-harmonic fits and the nodal tangents, respectively. (b) Doping dependences of the energies of nodal gap 2ΔN (blue circles), antinodal gap 2Δ* (red squares), arc-endpoint gap 2Δarc (green diamonds) and 8.5 kBTc (black curve). The error bars of ΔN and Δ* derive from the uncertainty of next-higher-harmonic fit. The error bars of Δarc mainly derive from those of θarc. (c) Same as b, but scaled by Tc. (d) Correlation between Tc and ΔN for Bi2212 from the present study (coloured circles). Also plotted are the data for optimally doped single-layer cuprates, Bi2Sr2−xLaxCu2Oy (open triangle)23 and La2−xSrxCuO4 (open diamond)25. (e) Normalized superconducting gaps Δ(θ)/Δ* as functions of θ for representative dopings. Coloured dotted curves denote the nodal-gap term, ΔN sin2θ. Black dashed and solid curves indicate the gaps expected in the high and low superfluid-density limits, respectively. (f) Square of nodal-to-antinodal gap ratio (ΔN/Δ*)2, which we propose as being proportional to ρs21,22. (g) Superconducting-peak ratio (SPR) in the antinodal ARPES spectrum of Bi2212, taken from Feng et al.6. It has been established that SPR is approximately proportional to ρs6. (h) Superfluid density, ρs≡λ−2, determined from magnetic penetration depth λ with alternating-current susceptibility (triangles)10 and from heat capacity (crosses)7.
