content_image/369310.jpg
<img src='content_image/369310.jpg'>

quasiparticle dispersion that accompanies the opening of a superconducting gap. A steep increase in Γ around 8.0 meV below the gap edges represents a second pronounced feature in the figure. Such a sudden increase in peak width, combined with the kinks visible in the spectra in Figure 1d-f, are clear indications that the low energy states are interacting with a bosonic mode at a well defined energy. 

We plot the mode energy, Ω$_{⃗}$ $_{k}$, obtained from the theoretical fits described below, the superconducing gap, Δ$_{⃗}$ $_{k}$, and the energy difference δ$_{⃗}$ k = | Ω$_{⃗}$ k − Δ$_{⃗}$ $_{k}$| as a function of Fermi surface angle in Figure 5. Remarkably it is found that over the region of Fermi surface investigated in this study δ$_{⃗}$ k has a nearly constant value of 8 meV. The gap energies, denoted by the dashed lines in Figure 2 have in the case of panel (a) been corrected for the peak shift caused by residual resolution broadening as indicated from simulation and in the case of panel (c) by considering the Fermi surface angle of the kink location as a function of Fermi surface angle φ according to the Δ( φ ) = Δ 0 cos(2 φ ) parametrization of the d-wave gap with Δ 0 = 40 meV. Great care must be taken in identifying the correct value of the 

