Electronic structure of Tb0.5Sr0.5MnO3

Abstract

We study the electronic structure of single-crystal ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$, a non-charge-ordered mixed-valent semiconductor which exhibits a glassy magnetic ground state. We use the techniques of soft x-ray photoemission, hard x-ray photoemission, x-ray absorption, and resonant photoemission spectroscopy to investigate the occupied and unoccupied electronic states of ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Core level photoemission and x-ray absorption spectroscopy allow us to determine the valence states of Tb, Sr, and Mn ions in ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Model charge transfer multiplet calculations of core level photoemission and x-ray absorption spectra are employed to separate out the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ states and confirm their relative concentrations. Resonant photoemission spectroscopy across the Mn $2p\text{\ensuremath{-}}3d$ threshold shows clear resonant enhancement of the Mn $3d$ partial density of states and two-hole correlation satellites. A Cini-Sawatzky analysis gives on-site Coulomb energy ${U}_{dd}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}5.5\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n}$ states and ${U}_{pd}$ = 0.7 $\mathrm{eV}\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n+1}{\underline{L}}^{1}$ states. The O $1s\text{\ensuremath{-}}2p$ resonant photoemission is used to identify the O $2p$ two-hole correlation satellite which provides ${U}_{pp}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}3.4\ifmmode\pm\else\textpm\fi{}0.2$ eV for the O $2p$ states. Valence band photoemission indicates a small-gap semiconductor ($<100$ meV) consistent with electrical transport measurements. The estimated electronic structure parameters of the on-site Coulomb energies, in combination with the charge transfer energy and the hybridization strength obtained from the model calculations, indicate that ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ is a strongly correlated charge transfer type semiconductor.