Orbital characters of three-dimensional Fermi surfaces in Eu 2-x Sr x NiO 4 as probed by soft-x-ray angle-resolved photoemission spectroscopy

The three-dimensional Fermi-surface structure of hole-doped metallic layered nickelate Eu${}_{2\ensuremath{-}x}$Sr${}_{x}$NiO${}_{4}$ ($x=1.1$), an important counterpart to the isostructural superconducting cuprate La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$, 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 $\ensuremath{\Gamma}$-centered $3{z}^{2}\ensuremath{-}{r}^{2}$-derived small electron pocket. This finding demonstrates that in the layered nickelate the $3{z}^{2}\ensuremath{-}{r}^{2}$ band resides close to the ${x}^{2}\ensuremath{-}{y}^{2}$ one in energy. The resultant multiband feature with varying orbital character as revealed may strongly work against the emergence of the high-temperature superconductivity.