Polarization dependence and symmetry analysis in indirect K-edge RIXS

TL;DR

This paper investigates polarization effects in Cu K-edge RIXS spectra of Nd2CuO4, revealing how electronic excitations and scattering geometry influence spectral features and their symmetry properties.

Contribution

It provides a detailed analysis of polarization dependence and symmetry in RIXS, linking observed spectral features to specific charge-transfer and d-d excitations with theoretical modeling.

Findings

Weak fourfold oscillations in azimuthal scans

Spectral weight decreases at high energy loss with scattering angle

Raman selection rules accurately model polarization effects

Abstract

We present a study of the charge-transfer excitations in undoped Nd2CuO4 using resonant inelastic X-ray scattering (RIXS) at the Cu K-edge. At the Brillouin zone center, azimuthal scans that rotate the incident-photon polarization within the CuO2 planes reveal weak fourfold oscillations. A comparison of spectra taken in different Brillouin zones reveals a spectral weight decrease at high energy loss from forward- to back-scattering. We show that these are scattered-photon polarization effects related to the properties of the observed electronic excitations. Each of the two effects constitutes about 10% of the inelastic signal while the '4p-as-spectator' approximation describes the remaining 80%. Raman selection rules can accurately model our data, and we conclude that the observed polarization-dependent RIXS features correspond to Eg and B1g charge-transfer excitations to non-bonding oxygen 2p bands, above 2.5 eV energy-loss, and to an Eg d->d excitation at 1.65 eV.