Polarization dependence of x-ray absorption spectra in Na_xCoO_2

Abstract

In order to shed light on the electronic structure of Na_xCoO_2, and motivated by recent Co L-edge X-ray absorption spectra (XAS) experiments with polarized light, we calculate the electronic spectrum of a CoO_6 cluster including all interactions between 3d orbitals. We obtain the ground state for two electronic occupations in the cluster that correspond nominally to all O in the O^{-2} oxidation state, and Co^{+3} or Co^{+4}. Then, all excited states obtained by promotion of a Co 2p electron to a 3d electron, and the corresponding matrix elements are calculated. A fit of the observed experimental spectra is good and points out a large Co-O covalency and cubic crystal field effects, that result in low spin Co 3d configurations. Our results indicate that the effective hopping between different Co atoms plays a major role in determining the symmetry of the ground state in the lattice. Remaining quantitative discrepancies with the XAS experiments are expected to come from composition effects of itineracy in the ground and excited states.

10 pages, 4 figures

References in corpus (5)

• Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
• 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
• Evidence of a single nonmagnetic Co3+ state in the Na1CoO2 cobaltate
• X-ray absorption spectroscopy on layered cobaltates Na_xCoO_2

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• Electronic structure and Fermi surface tolopogy of Na${}_x$CoO${}_2$
• From Hubbard bands to spin-polaron excitations in the doped Mott material Na${}_x$CoO${}_2$
• Emergent charge ordering in near half doped Na${}_{0.46}$CoO${}_2$
• Evidence for Oxygen Holes due to d-p Rehybridization in Thermoelectric Sr_{1-x}Rh_{2}O_{4}
• Quasiparticle dispersion near the Fermi surface in Na${}_x$CoO${}_2$