Origin of the insulating state in NaCuO₂

Abstract

We study the electronic structure of NaCuO₂ by analysing experimental core level photoemission and X-ray absorption spectra using a cluster as well as an Anderson impurity Hamiltonianincluding the band structure of the oxygen sublattice. We show that the X-ray absorption results unambiguously establish a negative value of the charge transfer energy, Δ. Further, mean-field calculations for the edge-shared one-dimensional CuO₂ lattice of NaCuO₂ within the multiband Hubbard Hamiltonian show that the origin of the insulating nature lies in the band structure rather than in the correlation effects. LMTO-ASA band structure calculations suggest that NaCuO₂ is an insulator with a gap of around 1 eV.