Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2

Abstract

We report ${}^{23}$Na and ${}^{59}$Co nuclear magnetic (NMR) and quadrupolar resonance (NQR) studies for the $x=2/3$ phase of the lamellar oxide Na${}_x$CoO${}_2$, which allowed us to establish reliably the atomic order of the Na layers and their stacking between the CoO${}_2$ slabs. We evidence that the Na${}^{+}$ order stabilizes filled non magnetic Co${}^{3+}$ ions on 25% of the cobalt sites arranged in a triangular sublattice. The transferred holes are delocalized on the 75% complementary cobalt sites which unexpectedly display a planar cobalt kagomé structure. These experimental results resolve a puzzling issue by precluding localized moments pictures for the magnetic properties. They establish that the quasi ferromagnetic properties result from a narrow band connecting a frustrated arrangement of atomic orbitals, and open the route to unravel through similar studies the electronic properties of the diverse ordered phases of sodium cobaltates.

arXiv comment6 pages, 5 figures. Accepted at EPL (Europhysics Letters)

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• Novel electronic states realized by the interplay between Li diffusion and Co${}^{3+}$$/$Co${}^{4+}$ charge ordering in Li${}_{\mathrm{x}}$CoO${}_2$
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• Phase segregation in NaxCoO2 for large Na contents
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• Origin of the electron disproportionation in the metallic sodium cobaltates
• Multiorbital kinetic effects on charge ordering of frustrated electrons on the triangular lattice
• Exploring the possibility of enhancing the figure-of-merit ( $>$ 2) of Na${}_{0.74}$CoO${}_2$: A combined experimental and theoretical study
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• From Friedel oscillations and Kondo effect to the pseudogap in cuprates
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• Complex magnetic differentiation of cobalts in Na${}_x$CoO${}_2$ with 22K Néel temperature
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• Ab-initio studying of spin states of sodium cobaltate Na${}_{2/3}$CoO${}_2$
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