Abstract

For a long time, the symmetry of excitons have been discussed (if at all) in the Wannier picture of hydrogen like (s, p, …) excitonic states. While this classification is valid in the limit of dilute (weakly bound) excitons, it ceases to be valid in the limit of tightly bound excitons in 2D materials, where the space group symmetry of the underlying crystal structure becomes important. I will present the results of the recent PhD thesis of Muralidhar Nalabothula who has implemented the full symmetry analysis (including non-symmorphic symmetries) of excitonic states calculated with the Bethe-Salpeter equation. Besides some beautiful colorful pictures of excitons, I will show some examples where the knowledge of the excitonic symmetries is helpful to understand the coupling with phonons and the selection rules of phonon-assisted luminescence spectroscopy.