Charge transfer model for the electronic structure of layered ruthenates

Krzysztof Rościszewski; Andrzej M. Oleś

doi:10.1103/PhysRevB.91.155137

paper

Charge transfer model for the electronic structure of layered ruthenates

arXiv:1504.06850 · doi:10.1103/PhysRevB.91.155137

Abstract

Motivated by the earlier experimental results and \textit{ab initio} studies on the electronic structure of layered ruthenates (Sr $_{2}$ RuO $_{4}$ and Ca $_{2}$ RuO $_{4}$ ) we introduce and investigate the multiband $d - p$ charge transfer model describing a single RuO $_{4}$ layer, similar to the charge transfer model for a single CuO $_{2}$ plane including apical oxygen orbitals in high $T_{c}$ cuprates. The present model takes into account nearest-neighbor anisotropic ruthenium-oxygen $d - p$ and oxygen-oxygen $p - p$ hopping elements, crystal-field splittings and spin-orbit coupling. The intraorbital Coulomb repulsion and Hund's exchange are defined not only at ruthenium but also at oxygen ions. Our results demonstrate that the RuO $_{4}$ layer cannot be regarded to be a pure ruthenium $t_{2 g}$ system. We examine a different scenario in which ruthenium $e_{g}$ orbitals are partly occupied and highlight the significance of oxygen orbitals. We point out that the predictions of an idealized model based on ionic configuration (with $n_{0} = 4 + 4 \times 6 = 28$ electrons per RuO $_{4}$ unit) do not agree with the experimental facts for Sr $_{2}$ RuO $_{4}$ which support our finding that the electron number in the $d - p$ states is significantly smaller. In fact, we find the electron occupation of $d$ and $p$ orbitals for a single RuO $_{4}$ unit $n = 28 - x$ , being smaller by at least 1--1.5 electrons from that in the ionic model and corresponding to self-doping with $x ≃ 1.5$ .

12 pages, 3 figures

Charge transfer model for the electronic structure of layered ruthenates

Abstract

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