Possible nodal superconducting gap and Lifshitz transition in heavily hole-doped Ba 0.1 K 0.9 Fe 2 As 2

We performed a high-energy resolution angle-resolved photoemission spectroscopy investigation of overdoped Ba0.1K0.9Fe2As2 with Tc=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 pairing interaction is not driven by the Fermi surface topology, but nevertheless reveals the possible importance of the Fermi surface topology in shaping the superconducting gap structure.