Possible nodal superconducting gap emerging at the Lifshitz transition in heavily hole-doped Ba0.1K0.9Fe2As2

TL;DR

This study uses ARPES to explore how the superconducting gap in heavily hole-doped Ba0.1K0.9Fe2As2 relates to Fermi surface changes, revealing a possible nodal gap emerging at a Lifshitz transition.

Contribution

It provides new insights into the superconducting gap structure and its relation to Fermi surface topology in heavily hole-doped iron-based superconductors.

Findings

Lifshitz transition occurs between x=0.7 and 0.9 doping levels.

Superconducting gap structure remains similar despite Fermi surface topology change.

A vertical node is observed at the tip of the off-M-centered Fermi surface pocket lobes.

Abstract

We performed a high energy resolution ARPES investigation of over-doped Ba0.1K0.9Fe2As2 with T_c= 9 K. The Fermi surface topology of this material is similar to that of KFe2As2 and differs from that of slightly less doped Ba0.3K0.7Fe2As2, implying that a Lifshitz transition occurred between x=0.7 and x=0.9. Albeit for a vertical node found at the tip of the emerging off-M-centered Fermi surface pocket lobes, the superconducting gap structure is similar to that of Ba0.3K0.7Fe2As2, suggesting that the paring interaction is not driven by the Fermi surface topology.