The momentum dependence of the superconducting gap in the cuprates has been debated, with most experiments reporting a deviation from a simple dx2−y2 form in the underdoped regime and a few experiments claiming that a simple dx2−y2 form persists down to the lowest dopings. We affirm that the superconducting gap function in sufficiently underdoped Bi2Sr2CaCu2O8+δ (Bi-2212) deviates from a simple \textit{d}-wave form near the antinode. This is observed in samples where doping is controlled only by oxygen annealing, in contrast to claims that this effect is only seen in cation-substituted samples. Moreover, a quasiparticle peak is present at the antinode down to p=0.08, refuting claims that a deviation from a simple \textit{d}-wave form is a data analysis artifact stemming from difficulty in assessing a gap in the absence of a quasiparticle.
@article{arxiv.1405.4961,
title = {Ubiquitous antinodal quasiparticles and deviation from simple d-wave form in underdoped Bi-2212},
author = {I. M. Vishik and M. Hashimoto and W. -S. Lee and T. P. Devereaux and Z. -X. Shen},
journal= {arXiv preprint arXiv:1405.4961},
year = {2017}
}