Martedì 6 Giugno alle ore 15.00 presso la sala "Giovanni Signorelli" (Edificio "Renato Ricamo") il Dott. Vitaly Gorelov (Laboratoire des Solides Irradiés (LSI), École Polytechnique Route de Saclay) terrà un seminario dal titolo
"Strongly bound delocalised excitons in complex oxides, its stability and dispersion: Example of V2O5 "
Abstract
The simplest picture of excitons in materials with atomic‐like localization of electrons is that of localized Frenkel excitons with a large binding energy. However, in complex materials, relevant for optoelectronic applications, this picture may break down, and a more sophisticated description is required [1].
In the first part of the talk, using the example of the layered oxide V2O5, I will show how localised charge‐transfer excitations combine to form excitons that have a huge binding energy and a large electron‐hole distance. I will explain this seemingly contradictory finding combining first‐principles many‐body perturbation theory calculations and ellipsometry experiments with a tight‐binding model that reflects the particular geometry. I will also discuss the dispersion of such excitons and how it is manifested in different spectroscopies [2]. Furthermore, in bulk and low‐dimensional extended systems, the screening of excitations by the electron cloud is a key feature governing spectroscopic properties. Widely used computational approaches, such as the GW approximation and the resulting approximate Bethe‐Salpeter equation, are explicitly formulated in terms of the screened Coulomb interaction.
In the second part of the talk I will explore the effect of screening in absorption and electron energy loss spectroscopy, concentrating on the effect of local distortions on the screening and elucidating the resulting changes in the various spectra [3]. Using the layered bulk oxide V2O5 as prototype material, I will show in which way local distortions affect the screening, and in which way changes in the screening impact electron energy loss and absorption spectra including excitons. This yields insight concerning the structure‐properties relations that are crucial for the use of V2O5 as energy storage material, and more generally, that may be used to optimize the analysis and the calculation of electronic spectra in complex materials.
References
[1] V. Gorelov et al., npj Comput. Mater. 8:94 (2022)
[2] V. Gorelov et al., arXiv:2304.08415 (2023)
[3] V. Gorelov et al., PRB 107, 075101 (2023)
In the first part of the talk, using the example of the layered oxide V2O5, I will show how localised charge‐transfer excitations combine to form excitons that have a huge binding energy and a large electron‐hole distance. I will explain this seemingly contradictory finding combining first‐principles many‐body perturbation theory calculations and ellipsometry experiments with a tight‐binding model that reflects the particular geometry. I will also discuss the dispersion of such excitons and how it is manifested in different spectroscopies [2]. Furthermore, in bulk and low‐dimensional extended systems, the screening of excitations by the electron cloud is a key feature governing spectroscopic properties. Widely used computational approaches, such as the GW approximation and the resulting approximate Bethe‐Salpeter equation, are explicitly formulated in terms of the screened Coulomb interaction.
In the second part of the talk I will explore the effect of screening in absorption and electron energy loss spectroscopy, concentrating on the effect of local distortions on the screening and elucidating the resulting changes in the various spectra [3]. Using the layered bulk oxide V2O5 as prototype material, I will show in which way local distortions affect the screening, and in which way changes in the screening impact electron energy loss and absorption spectra including excitons. This yields insight concerning the structure‐properties relations that are crucial for the use of V2O5 as energy storage material, and more generally, that may be used to optimize the analysis and the calculation of electronic spectra in complex materials.
References
[1] V. Gorelov et al., npj Comput. Mater. 8:94 (2022)
[2] V. Gorelov et al., arXiv:2304.08415 (2023)
[3] V. Gorelov et al., PRB 107, 075101 (2023)
