Multiplet calculations and interpretation of XAS and RIXS spectra at the Ti L3 Edge

• Grant number: 25/08025-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: September 01, 2025
• End date: August 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Thiago José de Almeida Mori
• Grantee: Raul Augusti Pereira
• Host Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Ministério da Ciência, Tecnologia e Inovação (Brasil). Campinas , SP, Brazil

Abstract

SrTiO3 is a perovskite oxide that exhibits a range of emergent properties - such as magnetism, ferroelectricity, and superconductivity - often associated with the presence of oxygen vacancies and changes in the titanium valence state, nominally Ti4+ (d0 configuration). Although X-ray absorption spectroscopy (XAS) at the Ti L3-edge is sensitive to these electronic changes, the origin of some spectral features - such as the broadening or splitting of the peak corresponding to the eg orbitals - remains controversial. Some recent studies attribute this broadening to the residual presence of Ti3+ (d1 configuration), even in pure samples. However, preliminary data obtained by our group, in both pure and doped samples, indicate that the broadening may also occur in the absence of Ti3+. These results suggest that other origins may be behind this spectral feature, such as non-local interactions or band effects. This type of effect has been discussed for decades in the case of TiO2-family oxides - with different structures - yet no consensus has been reached in the literature. In this project, we propose to investigate these issues through simulations of XAS and RIXS (resonant inelastic X-ray scattering) spectra using multiplet electronic calculations with the Crispy and Quanty softwares. The work plan includes a literature review, training in computational methods, and comparison with experimental spectra measured at the IPE beamline of Sirius. In doing so, we aim to contribute to the accurate interpretation of Ti oxide spectra and to the understanding of the emergent properties of SrTiO3 and other titanates. (AU)