Photoemission spectroscopy has become increasingly used to elucidate the electronic properties of materials, since it provides both quasi-particle band structures, with information of one-particle-like excitations, and satellite structures that reflect the coupling to bosonic excitations such as phonons, plasmons, magnons, etc.. Actuate descriptions of photoemission spectra from first principles have been a challenge for ages. Currently, the most widely used approach for moderately correlated materials is the GW approximation (GWA) proposed by L. Hedin in 1965 . However, one of its notable shortcomings is the poor description of the satellite structures in photoemission spectra. Alternatively, the cumulant expansion approximation (CEA) has been quite promising for giving a better description the full photoemission spectra in a number of systems [2-3].
In the first part of my talk, I will explain why GWA fails and how CEA improves the satellite spectra, using exactly solvable electron-boson coupling models. Moreover, the challenges of the CEA will be discussed, especially in the valence photoemission of metals. The second part of my talk will focus on the comparison between calculated and measured angle-resolved photoemission spectra (ARPES) where a straightforward intrinsic calculation is not sufficient due to the so-called extrinsic and interference effects, as well as the presence of the thermal motion of atoms. Our recent studies on bulk aluminum show how one can model the entire photoemission process beyond the sudden approximation and obtain a good agreement with experiment .
 L. Hedin Phys. Rev. 139, A796 (1965)
 Jianqiang Sky Zhou, et. al., Phys. Rev. B 97, 035137 (2018)
 Jianqiang Sky Zhou, et.al., arXiv:1811.12217
Spectroscopie des nouveaux états quantiques
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