Abrupt change in the energy gap of superconducting Ba1-xKxFe2As2 single crystals with hole doping

TL;DR

This study uses laser ARPES to investigate how superconducting gaps in Ba1-xKxFe2As2 change with doping, revealing an abrupt gap drop and Fermi surface disappearance at high doping levels, challenging existing theories.

Contribution

It provides detailed doping-dependent measurements of superconducting gaps and Fermi surface evolution, highlighting orbital contributions and abrupt changes not fully explained by current theories.

Findings

Outer hole Fermi surface gap drops abruptly at x > 0.6

Inner and middle Fermi surface gaps scale with Tc

Disappearance of electron Fermi surface at high 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 (SC) gaps in this compound. The gap size of the outer hole Fermi surface (FS) sheet around the Brillioun 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 browse the different contributions of X2-Y2 and XZ/YZ orbitals to superconductivity in BaK and can be hardly completely reproduced by the available theories on iron-based superconductors.