The origin of a$_{1g}$ and e$_g$' orderings in Na$_x$CoO$_2$

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dc.creatorPillay, D.
dc.creatorJohannes, M. D.
dc.creatorMazin, I. I.
dc.creatorAndersen, O. K.
dc.date2008-04-23
dc.date.accessioned2026-07-07T09:55:17Z
dc.date.available2026-07-07T09:55:17Z
dc.descriptionIt has often been suggested that correlation effects suppress the small e_g' Fermi surface pockets of NaxCoO_2 that are predicted by LDA, but absent in ARPES measurements. It appears that within the dynamical mean field theory (DMFT) the ARPES can be reproduced only if the on-site energy of the eg' 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 -200 meV to 315 meV in therms of the energy difference. In this work, we perform density functional theory calculations of this one-electron splitting Δ= ε_a1g-ε_e_g' for the full two-layer compound, Na2xCo2O4, accounting for the effects of Na ordering, interplanar interactions and octahedral distortion. We find that εa_1g-εe_g' 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. This field disproportionately affects the a_1g orbital which protrudes farther upward from the Co plane than the e_g' orbitals. We discuss also the secondary effects of octahedral compression and multi-orbital filling on the value of Δas a function of Na content. Our results indicate that if the e_g' pockets are indeed suppressed that can only be due to nonlocal correlation effects beyond the standard DMFT.
dc.description4 pages, 3 figures
dc.identifierhttps://arxiv.org/abs/0804.3768
dc.identifierhttp://arxiv.org/abs/0804.3768
dc.identifierPhys. Rev. B 78, 012501 (2008)
dc.identifierdoi:10.1103/PhysRevB.78.012501
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/166576
dc.subjectSuperconductivity
dc.subjectMaterials Science
dc.titleThe origin of a$_{1g}$ and e$_g$' orderings in Na$_x$CoO$_2$
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