Doping dependence of the electronic structure in phosphorus-doped ferropnictide superconductor BaFe2(As1−xPx)2studied by angle-resolved photoemission spectroscopy

Abstract

BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ is a unique iron-based superconductor, where the superconductivity is induced by the isovalent substitution of phosphorus (P) for arsenic (As). Unlike other iron pnictides, the superconducting gap in BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ has been suggested to contain nodal lines by various experiments. The exact nature of the isovalent doping and nodal gap are key open issues in building a comprehensive picture of the iron-based superconductors. With angle-resolved photoemission spectroscopy, we found that the P substitution in BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ alters the electronic structure significantly. With P doping, the hole and electron Fermi surface sheets expand simultaneously and the band velocities are enhanced indicating a suppression of electron correlations. Moreover, the P doping induces strong ${k}_{z}$ dispersion on the ${d}_{xz}$-originated band with significant mixing of the ${d}_{{z}^{2}}$ orbital around Z, while the ${d}_{xy}$-originated band and the electron pockets are relatively intact. These rule out theories suggesting that the nodal gap is due to the vanishing ${d}_{xy}$ hole pocket, while support those considering a ${d}_{{z}^{2}}$-dominated hole Fermi surface around Z being responsible. Our results are thus helpful to explain the nodal superconductivity in BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ and understand the role of lattice parameter or pressure effect in iron-based superconductors.