Figure 5: Extraction of the SC gap from dispersions and robustness of the pairing against the disappearance of FS.
From: Observation of strong electron pairing on bands without Fermi surfaces in LiFe1−xCoxAs
(a,b) Extracted band dispersions of 1% Co and 3% Co below (light blue squares) and above (pink circles) Tc. The energy error bars are determined by the s.d. of the fitted parameters. The momentum error bars are determined by our momentum resolution times a factor of 3, since we combined three nearby EDCs to reduce the noise level. A zoom into a narrower energy range in c,d show that the difference between the NS and the SC state is the largest at the βZ centre, and then gets smaller at high binding energies. The green dotted curves are the fitting results, which yield a similar SC gap as extracted from EDCs. (e) Comparison of the extracted SC gap from the experimental data and the expected ones from weak coupling theories. This shows that the SC gap observed on the α band is robust despite the disappearance of the α FS at the Γ point. This observation is incompatible with the weak coupling theory, in which the SC gap is expected to be sensitive to both the density-of-states near EF and impurity scattering.
