K-edge X-ray absorption spectra in transition metal oxides beyond the single particle approximation: shake-up many body effects

TL;DR

This paper demonstrates that shake-up many-body effects significantly influence K-edge X-ray absorption spectra in correlated transition metal oxides and proposes a method to incorporate these effects for more accurate spectral interpretation.

Contribution

It introduces a simple convolution approach combining first-principles calculations with photoemission spectra to account for shake-up effects in XANES of correlated materials.

Findings

Shake-up effects are present in NiO, CoO, and CuO spectra.

Convolution method improves spectral agreement with experiments.

Method reveals shake-up effects are common in correlated transition metal oxides.

Abstract

The near edge structure (XANES) in K-edge X-ray absorption spectroscopy (XAS) is a widely used tool for studying electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single particle approach, for example, has generally limited itself to the dominant dipolar cross-section. It has long been known however that effects beyond this approach should be taken into account, both due to the inadequacy of such calculations when compared to experiment and the presence of shake-up many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra and the question is firstly how to account for it theoretically and secondly how to verify it experimentally. By using state-of-the-art first principles electronic structure calculations and 1s photoemission measurements we demonstrate that shake-up many-body effects are present in K-edge XAS dipolar spectra of NiO, CoO and CuO at all energy scales. We show that shake-up effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross-section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shake-up effects in K-edge XANES of most correlated transition metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure.