Satellites in the Ti~1$s$ core level spectra of SrTiO$_3$ and TiO$_2$

Abstract

Satellites in core level spectra of photoelectron spectroscopy (PES) can provide crucial information on the electronic structure and chemical bonding in materials, in particular in transition metal oxides. This work explores satellites of the Ti 1s and 2p core level spectra of SrTiO3 and TiO2. Conventionally, soft X-ray photoelectron spectroscopy (SXPS) probes the Ti 2p core level, however, it is not ideal to fully capture satellite features due to its inherent spin-orbit-splitting (SOS). Here, hard X-ray photoelectron spectroscopy (HAXPES) provides access to the Ti 1s spectrum instead, which allows to study intrinsic charge responses upon core-hole creation without the complication from SOS and with favourable intrinsic line widths. The experimental spectra are theoretically analysed by two impurity models, including an Anderson impurity model (AIM) built on local density approximation (LDA) and dynamical mean-field theory (DMFT), and a conventional TiO6 cluster model. The theoretical results emphasise the importance of explicit inclusion of higher-order Ti-O charge-transfer processes beyond the nearest-neighbouring Ti-O bond to simulate the core level spectra of SrTiO3 and TiO2. The AIM approach with continuous bath orbitals provided by LDA+DMFT represents the experimental spectra well. Crucially, with the aid of the LDA+DMFT method this work provides a robust prescription of how to use the computationally-cheap cluster model in fitting analyses of core level spectra.