Figure 7. 2D colour plots of FT-QPI intensity ρ(θ, E) along the inner and outer contours of the central pattern in q-space.

(a,b) The FT-QPI pattern taken at 14.5 mV. The solid-line contours in a and b were expressed approximatively by R₁−r₁cos4θ and R₂+r₂cos4θ for outer and inner rings, respectively. (c,d) The FT-QPI intensity along the inner (a) and outer (b) rings at different angles taken from the fourfold symmetrized FT-QPI patterns in Fig. 6 with various energy values. The initial polar angle starts from the direction. The gap minimum locates in the direction for both contours. (e,f) The angle-dependent energy thresholds taken from the vertical line-cuts to the colour plots in c,d by using the intensity I=0.19, 0.24 (0.125, 0.147) for the inner (outer) rings in a,b, respectively. The gap minimum locates in the direction for both contours. The solid lines in e,f plots are the gap functions derived from the Dynes model fitting to the spectrum taken at 1.5 K. The error bars were determined from the deviations between the line-cut experimental data and the polynomial fitting curve for each angle.