Mapping the Optical Excitations with Electron Beams

Title: Mapping the optical excitations with electron beams
When: Monday, April 7, 2025, 12:00
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 5, Seminar Room (5th Floor)
Speaker: Nahid Talebi, Institute for Experimental and Applied Physics, Kiel University, Germany

Van der Waals materials have enabled an exquisite platform for exploring light-matter interactions at the nanoscale. Various forms of van der Waals materials have enabled the observation of strong-coupling effects, in the form of exciton-polaritons, in either a self-hybridized form or in combination with photonic cavities. Here, I will elaborate on the interaction between free electrons and thin films of van der Waals materials, and will show how electron beams can probe self-hybridized exciton-polaritons in transition metal dichalcogenide thin films [1], and describe through a sequential cathodoluminescence spectroscopy technique the formation of a coherent cathodoluminescence radiation from exciton polaritons as well as their decoherence time scale [2]. I will also discuss how exciton-plasmon interactions can be leveraged to control the band structure of a plasmonic crystal [3]. In addition, the formation of exciton polaritons in perovskites [4], hyperbolic exciton polaritons in Bi2Se3 [5], and hyperbolic plasmon-polaritons in borophene films [6] will be discussed and explored with electron beams.

References:

1. M. Taleb, F. Davoodi, F. Diekmann, K. Rossnagel and N. Talebi, “Charting the Exciton-Polariton Landscape of WSe2 Thin Flakes by Cathodoluminescence Spectroscopy,” Advanced Photonic Research 3, 2100124 (2022).
2. M. Taleb, M. Hentschel, K. Rossnagel, H. Giessen and N. Talebi, “Phase-Locked photon-electron interactions without a laser,” Nat. Phys. 19, 869–876 (2023).
3. F. Davoodi, M. Taleb, F. K. Diekmann, T. Coenen, K. Rossnagel, N. Talebi, “Tailoring the Band Structure of Plexcitonic Crystals by Strong Coupling,” ACS Photonics 9 (7), 2473–2482 (2022).
4. M. Black, M. Asadi, P. Darman, F. Schillmöller, S. Darbari, N. Talebi, “Long-range self-hybridized exciton polaritons in two-dimensional Ruddlesden-Popper perovskites,” arXiv:2405.02950.
5. R. Lingstädt, N. Talebi, M. Hentschel, S. Mashhadi, B. Gompf, M. Burghard, H. Giessen, P. A van Aken, “Interaction of edge exciton polaritons with engineered defects in the hyperbolic material Bi2Se3,” Communications Materials 2 (1), 1-11 (2021).
6. Y. Abdi, M. Taleb, S. Hajibaba, M. Moayedi, N. Talebi, “Two-dimensional borophene: In-plane hyperbolic polaritons in the visible spectral range,” arXiv:2404.13609.