Reaffirming the $d_{x^2-y^2}$ superconducting gap using the   auto-correlation angle-resolved photoemission spectroscopy of   Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta}$
  Knowledge of the gap function is important to understand the pairing mechanism for high-temperature ($T_\mathrm{c}$) superconductivity. However, Fourier transform scanning tunneling spectroscopy (FT STS) and angle-resolved photoemission spectroscopy (ARPES) in the cuprates have reported contradictory gap functions, with FT-STS results deviating strongly from a canonical $d_{x^2-y^2}$ form. By applying an "octet model" analysis to autocorrelation ARPES, we reveal that a contradiction occurs because the octet model does not consider the effects of matrix elements and the pseudogap. This reaffirms the canonical $d_{x^2-y^2}$ superconducting gap around the node, which can be directly determined from ARPES. Further, our study suggests that the FT-STS reported fluctuating superconductivity around the node at far above $T_\mathrm{c}$ is not necessary to explain the existence of the quasiparticle interference 
M. Hashimoto, R.-H. He, J. P. Testaud, W. Meevasana, R. G. Moore, D.   H. Lu, Y. Yoshida, H. Eisaki, T. P. Devereaux, Z. Hus...
cond-mat.supr-con cond-mat.str-el