Orbital characters of three-dimensional Fermi surfaces in Eu_(z-x)Sr_xNiO_4 as probed by soft-x-ray angle-resolved photoemission spectroscopy

摘要

The three-dimensional Fermi-surface structure of hole-doped metallic layered nickelate Eu_(2-x)Sr_xNiO_4(x = 1,1), an important counterpart to the isostructural superconducting cuprate La_(2-x)Sr_xCuO_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 Γ-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.