Lucia Reining - Fingerprints of excitonic effects in valence electron response properties

Abstract Excitation spectra of valence electrons are often influenced by interaction effects, even in the absence of strong correlation. In particular, excitonic effects may dominate absorption spectra. In this talk, we start by reminding how the ab initio solution of the Bethe-Salpeter equation allows one to understand excitonic effects in semiconductors and insulators that go beyond textbook exciton models [1]. We then compare absorption spectroscopy with electron energy loss and inelastic x-ray scattering, and we show some surprising excitonic effects at large momentum transfer. We will extend the discussion to coherent inelastic x-ray scattering [2] and what one may deduce from the spectra. Finally, we will point to limitations of the current formulations that are of both physics and technical nature, and sketch ways to overcome them. The need for a close link between theory and experiment will be particularly highlighted throughout the talk. The results that will be presented have mostly been obtained in collaboration with members of the Palaiseau Theoretical Spectroscopy Group and of the ETSF, and with colleagues from experimental groups. References [1]V. Gorelov, L. Reining, M. Feneberg, R. Goldhahn, A. Schleife, W. Lambrecht, M. Gatti, npj. Comput. Mater., 8, 94 (2022) [2]I. Reshetnyak, M. Gatti, F. Sottile, L. Reining, Phys. Rev. Research, 1, 032010 (2019)