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

Abstract

It 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.

arXiv comment4 pages, 3 figures

References in corpus (22)

• Fermi surface nesting and the origin of Charge Density Waves in metals
• Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
• Doped t-J Model on a Triangular Lattice: Possible Application to Na${}_x$CoO${}_2\cdot y$H${}_2$0 and Na${}_{1-x}$TiO${}_2$
• Fermi surface evolution and Luttinger theorem in Na${}_x$CoO${}_2$: a systematic photoemission study
• ARPES on Na${}_{0.6}$CoO${}_2$: Fermi surface, extended flat dispersion, and unusual band splitting
• Ferromagnetic fluctuation and possible triplet superconductivity in Na_xCoO_2*yH_2O: Fluctuation-exchange study of multi-orbital Hubbard model
• Electron correlation and Fermi surface topology of Na${}_x$CoO${}_2$
• Possible spin-triplet $f$-wave pairing due to disconnected Fermi surfaces in Na${}_x$CoO${}_2\cdot y$H${}_2$O
• Nesting, spin-fluctuations, and odd-gap superconductivity in NaxCoO2 yH2O
• The crucial importance of the $t_{2g}$--$e_g$ hybridization in transition metal oxides
• Complete d-Band Dispersion and the Mobile Fermion Scale in NaxCoO2
• Na Induced Correlations in Na${}_x$CoO${}_2$
• Effect of Dynamical Coulomb Correlations on the Fermi Surface of Na_0.3CoO_2
• Possibility of f-wave spin-triplet superconductivity in the CoO superconductor: a case study on a 2D triangular lattice in the repulsive Hubbard model
• Magnetic susceptibility study of hydrated and non-hydrated NaxCoO2-yH2O single crystals
• An ab-initio evaluation of the local effective interactions in the superconducting compound $Na\_0.35CoO\_2-1.3H\_2O$
• Destruction of the small Fermi surfaces in Na${}_x$CoO${}_2$ by Na disorder
• The low-energy ARPES and heat capacity of Na${}_{0.3}$CoO${}_2$: A DMFT study
• X-ray absorption spectroscopy on layered cobaltates Na_xCoO_2
• Interorbital charge transfers and Fermi-surface deformations in strongly correlated metals: models, BaVS${}_3$ and Na${}_x$CoO${}_2$
• Coulomb correlations do not fill the e'_g hole pockets in Na_{0.3}CoO_2
• Electronic theory for itinerant in-plane magnetic fluctuations in Na${}_x$CoO${}_2$

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