Electronic structure of Tb0.5 Sr0.5 MnO3

We study the electronic structure of single-crystal Tb0.5Sr0.5MnO3, 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 Tb0.5Sr0.5MnO3. Core level photoemission and x-ray absorption spectroscopy allow us to determine the valence states of Tb, Sr, and Mn ions in Tb0.5Sr0.5MnO3. Model charge transfer multiplet calculations of core level photoemission and x-ray absorption spectra are employed to separate out the Mn3+ and Mn4+ states and confirm their relative concentrations. Resonant photoemission spectroscopy across the Mn 2p-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 Udd∼5.5±0.2 eV for the Mn 3dn states and Upd = 0.7 eV±0.2 eV for the Mn 3dn+1L̲1 states. The O 1s-2p resonant photoemission is used to identify the O 2p two-hole correlation satellite which provides Upp∼3.4±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 Tb0.5Sr0.5MnO3 is a strongly correlated charge transfer type semiconductor.