Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering

Abstract

We report resonant X-ray scattering measurements on the orbitally-degenerate triangular metallic antiferromagnet 2H-AgNiO2 to probe the spontaneous transition to a triple-cell superstructure at temperatures below 365 K. We observe a strong resonant enhancement of the supercell reflections through the Ni K-edge. The empirically extracted K-edge shift between the crystallographically-distinct Ni sites of 2.5(3) eV is much larger than the value expected from the shift in final states, and implies a core-level shift of ~1 eV, thus providing direct evidence for the onset of spontaneous honeycomb charge order in the triangular Ni layers. We also provide band-structure calculations that explain quantitatively the observed edge shifts in terms of changes in the Ni electronic energy levels due to charge order and hybridization with the surrounding oxygens.

arXiv comment5 pages, 4 figures

References in corpus (3)

• Landau theory of charge and spin ordering in the nickelates
• Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2
• Charge disproportionation and collinear magnetic order in the frustrated triangular antiferromagnet AgNiO2

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• Revisiting the metal-to-metal transition in $2H$-AgNiO${}_2$