  The interplay between superconductivity and the pseudogap is an important
aspect of cuprate physics. However, the nature of the pseudogap remains
controversial, in part because different experiments have suggested different
gap functions. Here we present a photon-energy-dependence angle-resolved
photoemission spectroscopy (ARPES) study on
Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta}$. We find that
antinodal ARPES spectra at low photon energies are dominated by background
signals which can lead to a misevaluation of the spectral gap size. Once
background is properly accounted for, independent of photon energy, the
antinodal spectra robustly show two coexisting features at different energies
dominantly attributed to the pseudogap and superconductivity, as well as an
overall spectral gap which deviates from a simple d-wave form. These results
support the idea that the spectral gap is distorted due to the competition
between the pseudogap and superconductivity.
