Evidence for exclusion of the possibility of $d$-wave superconducting-gap symmetry in Ba-doped KFe$_2$As$_2$

TL;DR

This study uses laser-based angle-resolved photoemission spectroscopy to analyze how Ba doping affects the superconducting gap anisotropy in KFe$_2$As$_2$, providing evidence against $d$-wave symmetry and highlighting the role of fluctuations in pairing.

Contribution

It demonstrates that Ba doping alters the superconducting gap anisotropy and rules out $d$-wave symmetry in Ba-doped KFe$_2$As$_2$, emphasizing the importance of spin and orbital fluctuations.

Findings

Superconducting gap anisotropy varies with Ba doping.

$d$-wave symmetry is excluded in Ba-doped KFe$_2$As$_2$.

Spin and orbital fluctuations are key to pairing.

Abstract

We have investigated the superconducting(SC)-gap anisotropy for several Ba-doped KFe$_2$As$_2$ samples using laser-based angle-resolved photoemission spectroscopy. We show that the SC-gap anisotropy and node positions drastically change with a small amount of Ba doping. Our results totally exclude a possibility of $d$-wave symmetry and strongly suggest that both spin and orbital fluctuations are important for the paring interaction in the Ba-doped K122.