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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 18: SrTiO3: A Versatile Material from Bulk Quantum Paraelectric to 2D Superconductor: Poster (joint session TT/KFM/MA/O)
KFM 18.5: Poster
Wednesday, March 20, 2024, 15:00–18:00, Poster E
Role of excitonic effects in optical and x-ray absorption spectroscopy of SrTiO3: insights from a combined first principles and many-body theory approach — •V. Begum-Hudde1, M. E. Gruner2, and R. Pentcheva2 — 1University of Illinois Urbana-Champaign, USA. — 2University of Duisburg-Essen, Duisburg, Germany.
We present a comprehensive study of the optical[1] and x-ray absorption spectrum[2] (XAS) in the paradigmatic oxide, SrTiO3. Our results demonstrate that inclusion of the quasiparticle effects with single-shot G0W0 as well as the electron-hole (e-h), and electron-(core)hole interactions by solving the Bethe-Salpeter Equation (BSE) is integral to accurately describe both the valence and core electron excitations. For the optical spectra, the effect of the exchange-correlation functional is observed to progressively reduce from 1.5 eV variance in the onset of the spectrum in the independent particle picture to 0.3 eV upon inclusion of excitonic corrections. The Ti-L2,3 XAS edge is concurrent with experiment w.r.t. the energetic positions of the four-peak structure which is characteristic of Ti octahedral coordination in SrTiO3. We also analyze the origin of prominent peaks in the spectra and identify the orbital character of the relevant contributions by projecting the e-h coupling coefficients from the BSE eigenvectors on the band structure. The spatial distribution of the first bound exciton wave function of the O K edge exhibits an intriguing two-dimensional spread in the x-y plane despite the three-dimensional nature of the material.
[1] Phys. Rev. Mater. 3, 065004 (2019)
[2] Phys. Rev. Res. 5, 013199 (2023)