Weak-coupling superconductivity in electron-doped NaFe0.95Co0.05As revealed by ARPES

Abstract

We report a systematic study on the electronic structure and superconducting (SC) gaps in electron-doped NaFe${}_{0.95}$Co${}_{0.05}$As superconductor using angle-resolved photoemission spectroscopy. Holelike Fermi sheets are at the zone center and electronlike Fermi sheets are at the zone corner, and are mainly contributed by $xz$ and $yz$ orbital characters. Our results reveal a $\frac{\ensuremath{\Delta}}{{K}_{B}{T}_{c}}$ in the range of 1.8--2.1, suggesting a weak-coupling superconductivity in these compounds. Gap closing above the transition temperature (${T}_{c}$) shows the absence of pseudogaps. Gap evolution with temperature follows the BCS gap equation near the $\ensuremath{\Gamma}$, $Z$, and $M$ high symmetry points. Furthermore, an almost isotropic superconductivity along the ${k}_{z}$ direction in the momentum space is observed by varying the excitation energies.