Coherent Interaction of 2⁢𝑠 and 1⁢𝑠 Exciton States in Transition-Metal Dichalcogenide Monolayers

In a new study, scientists at the University of Bonn have tracked how excitons—bound pairs of electrons and holes—interact in monolayer tungsten diselenide (WSe₂), a widely studied two-dimensional semiconductor. The research, led by Dr. Andrea Bergschneider and Prof. Dr. Stefan Linden, sheds new light on the quantum behavior of excitons and could pave the way for the coherent manipulation of Rydberg polaritons in optical cavities. Using ultrafast pump-probe spectroscopy, the team observed coherent coupling between 1s and 2s exciton states—revealed through a measurable shift in the exciton resonance. An off-resonant pump pulse was used to create a virtual population of excitons in the material, while a resonant probe pulse monitored how these virtual states interacted with real excitons. To the researchers’ surprise, the interaction between 1s and 2s excitons closely resembled that between two 1s excitons—despite their different energy levels. Even more remarkably, the team was able to detect, for the first time, a bound state between 1s and 2s excitons. Such coherent interactions offer an important window into the fundamental behavior of excitons, and could be relevant for designing next-generation devices that harness quantum properties for novel technologies. Understanding and manipulating these effects may prove essential for the next generation of quantum optical experiments based on layered semiconductors. The full study has been published in Physical Review Letters.

Publication: Coherent Interaction of 2⁢𝑠 and 1⁢𝑠 Exciton States in Transition-Metal Dichalcogenide Monolayers. Max Wegerhoff, Moritz Scharfstädt, Stefan Linden and Andrea Bergschneider. Phys. Rev. Lett. – Accepted 12 June, 2025 DOI: https://doi.org/10.1103/PhysRevLett.134.236901

Discover more!