A loss for photoemission is a gain for Auger: Direct experimental evidence of crystal-field splitting and charge transfer in photoelectron spectroscopy

Abstract

We find a new 5 eV satellite in the Ti 1s photoelectron spectrum of the transition-metal oxide SrTiO$_3$. This satellite appears in addition to the well-studied 13 eV structure that is typically associated with the Ti 2p core line. We give direct experimental evidence that the presence of two satellites is due to the crystal-field splitting of the metal 3d orbitals. They originate from ligand 2p t$_{2g}$ $\rightarrow$ metal 3d t$_{2g}$ and ligand 2p e$_g$ $\rightarrow$ metal 3d e$_g$ monopole charge-transfer excitations within the sudden approximation of quantum mechanics. This assignment is made by the energetics of the resonant and high-energy threshold behaviors of the Ti K-L$_2$L$_3$ Auger decay that follows Ti 1s photo-ionization.