2008/04/23 by D. Pillay, Devina Pillay, M. D. Johannes +2 · 1 citation
Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Copper-based nanomaterials and applications #Physics of Superconductivity and Magnetism #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.78.012501
published as Phys. Rev. B 78, 012501 (2008) · 4 pages, 3 figures
arxiv created 2008/04/23 · openalex publication_date 2008/07/08 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
It has often been suggested that correlation effects suppress the small eg^\ensuremath' Fermi-surface pockets of NaxCoO2 that are predicted by LDA, but absent in ARPES measurements. It appears that within the dynamical mean-field theory (DMFT) the ARPES results can be reproduced only if the on-site energy of the eg^\ensuremath' complex is lower than that of the a1g complex at the one-electron level, prior to the addition of local correlation effects. Current estimates regarding the order of the two orbital complexes range from \ensuremath-200 to 315 meV in terms of the energy difference. In this work, we perform density-functional theory calculations of this one-electron splitting \ensuremathΔ=ϵ_a1g\ensuremath-ϵ_eg^\ensuremath' for the full two-layer compound, accounting for the effects of Na ordering, interplanar interactions and octahedral distortion. We find that ϵ_a1g\ensuremath-ϵ_eg^\ensuremath' is negative for all Na fillings and that this is primarily due to the strongly positive Coulomb field created by Na+ ions in the intercalant plane that disproportionately affects the extended a1g orbital. We discuss also the effects of octahedral compression and multiorbital filling on the value of \ensuremathΔ as a function of Na content. Our results indicate that if the eg^\ensuremath' pockets are indeed suppressed, that can only be due to nonlocal correlation effects beyond the standard DMFT.