While the superconducting transition temperature of hole-doped Ba_{1-x}K_{x}Fe_{2}As_{2} decreases past optimal doping, superconductivity does not completely disappear even for the fully doped KFe_{2}As_{2} compound. In fact, superconductivity is robust through a Lifshitz transition where electron bands become hole-like around the zone corner at around x=0.7, thus challenging the conventional understanding of superconductivity in iron-based systems. High-resolution angle-resolved photoemission spectroscopy is used to investigate the superconducting gap structure, as well as the normal state electronic structure, around optimal doping and across the Lifshitz transition. Our findings reveal a largely orbital-dependent superconducting gap structure, where the more strongly correlated d_{xy} band has a vanishing superconducting gap at higher doping, aligning with the Hund's metal behavior observed in the normal state. Notably, the superconducting gap on the d_{xy} band disappears before the Lifshitz transition, suggesting that the Fermi surface topology may play a secondary role. We discuss how these results point to orbital-selective superconducting pairing and how strong correlations via Hund's coupling may shape superconducting gap structures in iron-based and other multiorbital superconductors.
@article{arxiv.2510.06435,
title = {Hund's coupling assisted orbital-selective superconductivity in Ba1-xKxFe2As2},
author = {Elena Corbae and Rong Zhang and Cong Li and Kunihiro Kihou and Chul-Ho Lee and Makoto Hashimoto and Thomas Devereaux and Oscar Tjernberg and Egor Babaev and Dung-Hai Lee and Vadim Grinenko and Donghui Lu and Zhi-Xun Shen},
journal= {arXiv preprint arXiv:2510.06435},
year = {2025}
}