Fig. 2: Temperature dependence of the energy gap and the associated spectral weight along a Fermi surface.

a Photoemission spectra (EDCs) measured at different temperatures at the Fermi momentum on the right side of the outer Fermi surface (k_F_OR) along the momentum Cut 1. The location of the momentum Cut 1 is illustrated in Fig. 1a and the location of the Fermi momentum k_F_OR is shown in the upper-right inset. b The corresponding symmetrized EDCs at different temperatures obtained from (a). c EDCs at different temperatures obtained from dividing the original EDCs in (a) by their corresponding Fermi distribution functions (FD Function). The solid black line at the bottom represents the fitted curve of the 103 K data by two Lorentzians which correspond to two bands, the outer-right band is at the Fermi level while the other inner-right one lies ~20 meV above the Fermi level as indicated by two arrows. d, e EDCs at different temperatures obtained from dividing the EDCs in (c) by the fitted curve at 103 K. For clarity, the obtained normalized EDCs are displayed in (d, e). f Temperature dependence of the energy gap. The black circles show the energy gap obtained by picking the peak position of the symmetrized EDCs in (b). The red circles show the gap obtained by picking the peak position of the normalized EDCs in (d, e). The dashed lines show the fitted curve of the energy gap by the BCS formula. g Temperature dependence of the spectral weight obtained from the normalized EDCs in (d, e). As shown in the upper-right inset, here we take three spectral intensities: the height of the peak below the Fermi level, the height of the dip at the Fermi level and the difference between the peak height and the dip height (PDD). The corresponding three spectral intensities as a function of temperature are shown by the empty black circles, empty blue circles and the red solid circles, respectively. Error bars reflect the uncertainty in determining the EDC peak position and spectral intensity.