Physics Seminars
Dark excitons in atomically thin semiconductors and how to make them bright
Speaker: Prof. Dr. Andreas Knorr (Technische University Berlin)
Date: Thursday 25 April 2024
Time: 15:00
Venue: T/2.09 in Trevithick building
Atomically thin semiconductors constitute a remarkable playground for exciton physics in two dimensions. This involves optically accessible (bright) as well as spin- and momentum-forbidden (dark) excitonic states for intra- and interlayer excitations. Momentum-dark excitons outside the optical light cone can typically be excited by momentum transfer resulting from (a) phonon scattering [1], or by (b) spatially structured optical near-fields [2-4] and (c) directly studied by photoelectron spectroscopy {5[. In this talk, we theoretically address the questions: (a) whether -at increasing densities and under exciton-phonon scattering- dark excitons can be approximated as a weakly interacting boson gas or are possibly dominated their fermionic substructure [1], (b) how spatially structured near-fields can be induced by nanostructures (such as molecules [3] or metal nanoparticles [4,5]) to excite dark in-plane excitons, and (c) how dark exciton dynamics can be followed via tr-ARPES. Throughout the talk, a comparison with recent experiments (absorption, luminescence and angle resolved photoemission spectroscopy) will be provided.[1] M. Katzer et al., Phys. Rev. B 108, L121102 (2023). [2] M. Katzer et al., Phys. Rev. B 107, 035304 (2023). [3] R. Salzwedel et al., Phys. Rev. B 109, 035309 (2024). [4] L. Greten et al, arXiv preprint arXiv:2309.09673 (2023). [5] S. Dong et al., Nature Communications 14, 5057 (2023).