Theoretical Analysis of Resonant Inelastic X-Ray Scattering Spectra in LaMnO3

TL;DR

This paper provides a theoretical analysis of RIXS spectra in LaMnO3 using Green-function formalism, multi-orbital models, and RPA, successfully matching experimental spectral features and energy dependence.

Contribution

It introduces a comprehensive theoretical framework for RIXS in LaMnO3, emphasizing band-to-band transitions over orbiton models, and achieves good agreement with experimental data.

Findings

RIXS spectra are well described by band-to-band transitions.

Correlation effects significantly modify spectral shape.

The incident-photon-energy dependence matches experiments.

Abstract

We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the K edge of Mn in the antiferromagnetic insulating manganite LaMnO3. We make use of the Keldysh-type Green-function formalism, in which the RIXS intensity is described by a product of an incident-photon-dependent factor and a density-density correlation function in the 3d states. We calculate the former factor using the 4p density of states given by an ab initio band structure calculation and the latter using a multi-orbital tight-binding model. The ground state of the model Hamiltonian is evaluated within the Hartree-Fock approximation. Correlation effects are treated within the random phase approximation (RPA). We obtain the RIXS intensity in a wide range of energy-loss 2-15 eV. The spectral shape is strongly modified by the RPA correlation, showing good agreement with the experiments. The incident-photon-energy dependence also agrees well with the experiments. The present mechanism that the RIXS spectra arise from band-to-band transitions to screen the core-hole potential is quite different from the orbiton picture previously proposed, enabling a comprehensive understanding of the RIXS spectra.