Abrupt change in the energy gap of superconducting Ba1−𝑥��K𝑥��Fe2As2 single crystals with hole doping

Abstract

We performed a laser angle-resolved photoemission spectroscopy (ARPES) study on a wide doping range of Ba1−𝑥K𝑥Fe2As2 (BaK) and precisely determined the doping evolution of the superconducting gaps in this compound. The gap size of the outer hole Fermi-surface (FS) sheet around the Brillouin zone (BZ) center shows an abrupt drop with overdoping (for 𝑥≳ 0.6) while the inner and middle FS gaps roughly scale with 𝑇𝑐. This is accompanied by the simultaneous disappearance of the electron FS sheet with similar orbital character at the BZ corner. These results indicate the different contributions of 𝑋2−𝑌2 and 𝑋⁢𝑍/𝑌⁢𝑍 orbitals to superconductivity in BaK and can hardly be completely reproduced by the available theories on iron-based superconductors.