Nature of the apical and planar oxygen bonds in the Sr${}_{n+1}$Ru${}_{n}$O${}_{3n+1}$ family ($n=1,2,3$)

Nature of the apical and planar oxygen bonds in the Sr $_{n + 1}$ Ru $_{n}$ O $_{3 n + 1}$ family ( $n = 1, 2, 3$ )

M. Malvestuto, V. Capogrosso, E. Carleschi, L. Galli, E. Gorelov, E. Pavarini, R. Fittipaldi, F. Forte, M. Cuoco, A. Vecchione, and F. Parmigiani

Phys. Rev. B 88, 195143 – Published 22 November 2013

Abstract

We investigate the electronic structure of the Sr $_{n + 1}$ Ru $_{n}$ O $_{3 n + 1}$ family $(n = 1, 2, 3)$ in the vicinity the Fermi level by means of polarization-dependent resonant O 1 $s$ x-ray emission spectroscopy. Using both energy window and polarization analysis we disentangle the contribution of apical and planar oxygen, and compare it with first-principles calculations. Our results provide a new insight on the nature of the oxygen bonds and the role of Sr $3 d$ states.

Received 8 August 2013

DOI:https://doi.org/10.1103/PhysRevB.88.195143

Authors & Affiliations

M. Malvestuto^1,2,*, V. Capogrosso^1,2, E. Carleschi³, L. Galli^4,5, E. Gorelov⁶, E. Pavarini^6,7, R. Fittipaldi^8,9, F. Forte^8,9, M. Cuoco^8,9, A. Vecchione^8,9, and F. Parmigiani^1,2

¹Elettra-Sincrotrone Trieste, S.S. 14 km 163.5, Area Science Park, I-34149 Basovizza (Ts), Italy
²Department of Physics, University of Trieste, via A. Valerio 2, I-34127, Trieste, Italy
³Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
⁴Center for Free-Electron Laser Science (CFEL), DESY, Notkestrasse 85, D-22607 Hamburg, Germany
⁵Department of Physics, University of Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany
⁶Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany
⁷JARA High-Performance Computing, RWTH Aachen, D-Aachen, Germany
⁸CNR-SPIN Salerno, Via Giovanni Paolo II, I-84084 Fisciano (SA), Italy
⁹Department of Physics, University of Salerno, Via Giovanni Paolo II, I-84084 Fisciano (SA), Italy

^*marco.malvestuto@elettra.eu

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Vol. 88, Iss. 19 — 15 November 2013

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Figure 1
Crystal structure of the single-layered perovskite Sr $_{2}$ RuO $_{4}$ . Each Ru atom is surrounded by an octahedron constituted by six O atoms and by a cubic Sr cage. The $c$ axis is perpendicular to the perovskite layers, and the $a b$ plane is parallel to the plane formed by Ru atoms in a given perovskite layer.Reuse & Permissions
Figure 2
O $K$ XES (circles) and XAS (triangles) spectra for the SRO series, measured at room temperature. The displayed XES spectra are recorded with excitation energy of 560 eV, well above the absorption threshold, i.e., off-resonance; at this energy the polarization dependence is basically negligible. The XAS spectra are shown for both polarization ${\vec{ɛ}}_{c}$ parallel to the $c$ axis (horizontal, dark lines) and polarization ${\vec{ɛ}}_{a b}$ parallel to the the $a b$ plane (vertical, light lines). For each system the linear dichroism [ $δ I_{LD} (E) = I_{XAS} (E; {\vec{ɛ}}_{c}) - I_{XAS} (E; {\vec{ɛ}}_{a b})$ ] is then shown (gray areas). The XAS data are from Ref. 8. All spectra are arranged together on a common energy axis.Reuse & Permissions
Figure 3
(Top row) O $K$ -edge XAS of the SRO series ( $n = 1, 2, 3$ ) for horizontal and vertical polarization, ${\vec{ɛ}}_{c}$ and ${\vec{ɛ}}_{a b}$ . The numbered dots indicate the excitation photon energies at which the XES spectra (bottom row panels) are recorded. (Bottom row) O $K$ -edge ( $2 p \to 1 s$ ) XES spectra obtained at room temperature for several excitation energies and both horizontal and vertical polarization. For a given system and polarization the spectra are shifted vertically by a constant offset to the energy of incident exciting photons (numbered dots in the upper row panels). The spectra consist of elastically scattered light (the elastic peak, vertical dotted line) and an inelastic spectrum, composed by three main spectral features ( $α$ , $β$ , and $γ$ ). The XES spectra are plotted vs the difference between the energy of the emitted and that of the incident photon (energy loss).Reuse & Permissions
Figure 4
(a) XES O $K$ -edge spectrum of Sr $_{2}$ RuO $_{4}$ (black line) at the excitation energy 528.1 eV, horizontal polarization. The spectrum can be decomposed into three Lorentzian functions centered at $-$ 7, $-$ 4.6, and $-$ 1.3 eV, respectively (dashed lines). (b) Calculated O $_{a}$ 2 $p_{z}$ (dotted line) and O $_{p}$ $2 p_{z}$ (solid line) contributions to the XES spectra in horizontal polarization, broadened by an instrumental resolution $Δ E = 0.66$ eV.Reuse & Permissions
Figure 5
The two upper panels show the off-resonance XES and the XAS spectra for vertical (left column, triangles) and horizontal (right column, circles) polarization. The solid curves in the remaining panels show the most relevant partial density of states contributing to the spectra. The in-plane density of states are shown on the left and the out-of-plane density of states on the right. For the O $_{p}$ $2 p_{x}, 2 p_{y}$ , and $2 p_{z}$ contributions, the lines show the corresponding partial density of states shifted by $\sim$ 1.3 eV to account for the O $1 s$ core-level energy difference between apical and planar oxygens. The shift is indicated by an arrow. The experimental data and the partial density of states are plotted on a common energy scale. For the experimental data we take as energy zero the absorption threshold, $E_{0} \sim 528$ eV.Reuse & Permissions
Figure 6
Intensity $I$ $_{α}$ of the resonant peak $α$ normalized with respect to the intensity $I$ $_{β}$ of the nonresonant peak $β$ as a function of the excitation photon energies. Black solid dots, ${\vec{ɛ}}_{c}$ ; solid triangles, ${\vec{ɛ}}_{a b}$ . The arrows in panel (a) indicate the energy ranges of the 2 $p$ states of the apical and planar oxygens; the vertical dashed lines show the position of the elastic peak.Reuse & Permissions

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