Fig. 3: Signatures of the opposite gap sign in the momentum dependence of the Bogoliubov band hybridization in Bi2212.

a Fermi surface mapping of Bi2212 measured at 15 K. The covered momentum space is in the second quadrant as shown by the dashed black frame in c. The AB Fermi surface is mainly observed but is broken into two branches, Branch1 (pink line) and Branch2 (purple line), due to hybridization with the superstructure BB_SS Fermi surface. b Band structures measured along different momentum cuts around the crossing area of the initial Fermi surface AB and BB_SS. The images are obtained by dividing the Fermi distribution function to show part of the band structure above the Fermi level. The location of the momentum cuts is shown by the solid black lines in c and also be defined by the Fermi surface angle, θ. Two bands are mainly observed as marked by pink arrows for the Branch1 (BR1) and purple arrows for the Branch2 (BR2). c Schematic Fermi surface in the second quadrant with the related initial main AB Fermi surface and the superstructure BB_SS Fermi surface plotted. The gap sign on the Fermi surface is marked by the red color for the positive and the blue color for the negative by considering d-wave pairing symmetry. d Simulated Fermi surface of Bi2212 by considering the opposite gap sign on the AB and BB_SS Fermi surface in the Fermi surface crossing area. e The corresponding simulated band structures along different momentum cuts. f, g Same as d, e but by considering the same gap sign on the AB and BB_SS Fermi surface. h Momentum dependence of the Bogoliubov hybridization gap Δ_h. The definition of Δ_h is schematically shown in the upper insets. The measured values (see Supplementary Fig. 4) are plotted as black circles. The red (blue) line shows the simulated Δ_h by considering the opposite (same) gap sign of the main band AB and the superstructure band BB_SS. Error bars are determined based on the fitting error of the EDC peak position.