Intra- and intersite electronic excitations in multiferroicTbMnO3probed by resonant inelastic x-ray scattering

Abstract

$\text{Mn}\text{ }3d$ valence states and elementary electronic excitations in single-crystalline ${\text{TbMnO}}_{3}$ were probed with resonant inelastic x-ray scattering (RIXS) (or resonant x-ray emission spectroscopy, RXES), polarized x-ray absorption spectra and ab initio electron-structure calculations. Polarized $\text{Mn}\text{ }K$-edge x-ray absorption spectra of ${\text{TbMnO}}_{3}$ crystals exhibit a significant anisotropy along three crystallographic directions, particularly for the white-line region. The $1s3p$-RXES spectra obtained at the $\text{Mn}\text{ }K$ edge reveal that the quadrupolar Raman regime is restricted predominantly to below the pre-edge peak whereas the fluorescence regime starts from the first pre-edge peak of $1s\ensuremath{\rightarrow}3d$ transitions, indicating a relatively delocalized character of unoccupied $\text{Mn}\text{ }3d$ states. The additional $\text{K}\ensuremath{\beta}$ emission profile at energy loss $\ensuremath{\sim}62\text{ }\text{eV}$ is attributed to the off-site dipole $\text{Mn}\text{ }1s{\text{-Mn}}^{\ensuremath{'}}\text{ }3d$ and/or $\text{Mn}\text{ }1s\text{-Tb}\text{ }5d$ transitions, originating from hybridization between $\text{Mn}\text{ }4p$ states and neighboring ${\text{Mn}}^{\ensuremath{'}}\text{ }3d/\text{Tb}\text{ }5d$ states. The off-site dipole transition makes a considerable contribution to the pre-edge region of $\text{Mn}\text{ }K$-edge spectrum. Three prominent RIXS features at $\ensuremath{\sim}2.9$, 7, and 11 eV were observed. Based on $\text{GGA}+U$ calculations, the 7 eV region corresponds to transitions from $\text{O}\text{ }2p$ states to unoccupied minority $\text{Mn}\text{ }3d$ states, whereas the 11 eV band is ascribed to transitions from the $\text{O}\text{ }2p$ band to the empty $\text{Tb}\text{ }5d$ band. The broad 2.9 eV band is attributed to the coexistence of on-site $\text{Mn}\text{ }3d\text{-Mn}\text{ }3d$ and off-site $\text{Mn}\text{ }3d{\text{-Mn}}^{\ensuremath{'}}\text{ }3d$ transitions.