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Delocalization of dark and bright excitons in flat-band materials and the optical properties of V2O5

Abstract : Abstract The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V 2 O 5 , we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but, at the same time, a large electron-hole distance, and we explain this seemingly contradictory finding. The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure, whereas the exciton extends orthogonally to the chains formed by the crystal structure. Moreover, we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy. These findings are obtained by combining first principles many-body perturbation theory calculations, ellipsometry experiments, and tight binding modelling, leading to very good agreement and a consistent picture. Our explanation is general and can be extended to other materials.
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https://hal.archives-ouvertes.fr/hal-03658525
Contributor : Vitaly Gorelov Connect in order to contact the contributor
Submitted on : Wednesday, May 4, 2022 - 9:55:45 AM
Last modification on : Monday, May 30, 2022 - 5:36:02 PM

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Vitaly Gorelov, Lucia Reining, Martin Feneberg, Rüdiger Goldhahn, André Schleife, et al.. Delocalization of dark and bright excitons in flat-band materials and the optical properties of V2O5. npj Computational Materials, Springer Nature, 2022, 8 (1), pp.94. ⟨10.1038/s41524-022-00754-2⟩. ⟨hal-03658525⟩

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