Analysis of resonant inelastic x-ray scattering at the $K$ edge in NiO

TL;DR

This paper presents a theoretical analysis of Ni K-edge RIXS spectra in NiO, achieving quantitative agreement with experiments by incorporating band structure calculations and electron correlations.

Contribution

The authors develop a comprehensive theoretical framework combining Green's functions, band structure, and RPA to accurately model RIXS spectra in NiO.

Findings

Two main peaks at 5 eV and 8 eV in RIXS spectra

The 5 eV peak exhibits dispersion, the 8 eV peak does not

Band-to-band transitions augmented by RPA explain the peaks

Abstract

We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the Ni $K$ edge in an antiferromagnetic insulator NiO by applying the theory developed by the present authors. It is based on the Keldysh Green's function formalism, and treats the core-hole potential in the intermediate state within the Born approximation. We calculate the single-particle energy bands within the Hartree-Fock approximation on the basis of the multi-orbital tight-binding model. Using these energy bands together with the $4p$ density of states from an ab initio band structure calculation, we calculate the RIXS intensities as a function of energy loss. By taking account of electron correlation within the random phase approximation (RPA), we obtain quantitative agreement with the experimental RIXS spectra, which consist of prominent two peaks around 5 eV and 8 eV, and the former shows considerable dispersion while the latter shows no dispersion. We interpret the peaks as a result of a band-to-band transition augmented by the RPA correlation.