Orbital characters of three-dimensional Fermi surfaces in Eu2-xSrxNiO4 as probed by soft-x-ray angle-resolved photoemission spectroscopy

The three-dimensional Fermi-surface structure of hole-doped metallic layered nickelate Eu2-xSrxNiO4 (x = 1.1), an important counterpart to the isostructural superconducting cuprate La2-xSrxCuO4, is investigated by energy-dependent soft-x-ray angle-resolved photoemission spectroscopy. In addition to a large cylindrical hole Fermi surface analogous to the cuprates, we observe a Gamma-centered 3z(2) - r(2)-derived small electron pocket. This finding demonstrates that in the layered nickelate the 3z(2) - r(2) band resides close to the x(2) - y(2) one in energy. The resultant multiband feature with varying orbital character as revealed may strongly work against the emergence of the high-temperature superconductivity.