Anisotropic band properties of the linear-chain nickelateY2BaNiO5

The nonmagnetic band structure of ${\mathrm{Y}}_2$ ${\mathrm{BaNiO}}_5$, an orthorhombic nickelate that contains one-dimensional (1D) chains of vertex-linked ${\mathrm{NiO}}_6$ octahedra, has been calculated in the local-density approximation with the use of the linear augmented-plane-wave method. Neglecting magnetic effects, the results imply metallic behavior that originates from partially filled Ni(3d) conduction bands with ${\mathit{e}}_{\mathit{g}}$ character. This ${\mathit{e}}_{\mathit{g}}$ manifold is composite in nature, featuring a relatively narrow (∼0.3 eV) ${\mathrm{\delta }}^{\mathrm{*}}$-type level amid a broader (∼2 eV) ${\mathrm{\sigma }}^{\mathrm{*}}$ subband with well-defined 1D characteristics. At half filling, for example, the components of the ${\mathrm{\sigma }}^{\mathrm{*}}$-band Fermi-velocity squared 〈${\mathit{v}}_{\mathit{F}}^2$〉 perpendicular to the chain axis are only ∼1–2 % of the corresponding parallel value. Although antiferromagnetism is expected to induce insulating behavior in this system, the present results may be relevant in doped systems if magnetism can be suppressed.