Universality of superconducting gaps in overdoped Ba0.3K0.7Fe2As2 observed by angle-resolved photoemission spectroscopy

TL;DR

This study uses angle-resolved photoemission spectroscopy to show that the superconducting gaps in overdoped Ba0.3K0.7Fe2As2 are nearly isotropic and scale with $T_c$, supporting the universality of short-range pairing with $s_{\pm}$-wave symmetry.

Contribution

It demonstrates the universality of superconducting gap behavior across doping levels, highlighting short-range pairing mechanisms in iron-based superconductors.

Findings

Superconducting gaps are nearly isotropic on each Fermi surface.

Gap values scale with $T_c$ across doping levels.

Multiple nodeless gaps fit by a single gap function suggest universal pairing.

Abstract

We have performed angle-resolved photoemission spectroscopy on the overdoped Ba$_{0.3}$K$_{0.7}$Fe$_2$As$_2$ superconductor ($T_c$ = 22 K). We demonstrate that the superconducting (SC) gap on each Fermi surface (FS) is nearly isotropic whereas the gap value varies from 4.4 to 7.9 meV on different FSs. By comparing with under- and optimally-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$, we find that the gap value on each FS nearly scales with $T_c$ over a wide doping range (0.25 $\textyen leq$ $x$ $\textyen leq$ 0.7). Although the FS volume and the SC gap magnitude are strongly doping dependent, the multiple nodeless gaps can be commonly fitted by a single gap function assuming pairing up to the second-nearest-neighbor, suggesting the universality of the short-range pairing states with the $s_{\yenpm}$-wave symmetry.