Electronic structure of Tb0.5Sr0.5MnO3

Abstract

We study the electronic structure of single-crystal Tb 0.5 Sr 0.5 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 Tb 0.5 Sr 0.5 MnO 3 . Core level photoemission and x-ray absorption spectroscopy allow us to determine the valence states of Tb, Sr, and Mn ions in Tb 0.5 Sr 0.5 MnO 3 . Model charge transfer multiplet calculations of core level photoemission and x-ray absorption spectra are employed to separate out the Mn 3+ and Mn 4+ 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 U dd ∼ 5.5 ± 0.2 eV for the Mn 3d n states and U pd = 0.7 eV ± 0.2 eV for the Mn 3d n+1 L 1 states. The O 1s-2p resonant photoemission is used to identify the O 2p two-hole correlation satellite which provides U pp ∼ 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 Tb 0.5 Sr 0.5 MnO 3 is a strongly correlated charge transfer type semiconductor.