Ultrafast Exciton Dynamics in the Atomically Thin van der Waals Magnet CrSBr

• Published in: Nano letters Vol. 24; no. 14; pp. 4101 - 4107
• Main Authors: Meineke, Christian, Schlosser, Jakob, Zizlsperger, Martin, Liebich, Marlene, Nilforoushan, Niloufar, Mosina, Kseniia, Terres, Sophia, Chernikov, Alexey, Sofer, Zdenek, Huber, Markus A., Florian, Matthias, Kira, Mackillo, Dirnberger, Florian, Huber, Rupert
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10.04.2024
• Subjects: atomically thin solids; femtosecond near-field microscopy; ultrafast dynamics; terahertz; van der Waals magnets; anisotropic excitons
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.3c05010

Among atomically thin semiconductors, CrSBr stands out as both its bulk and monolayer forms host tightly bound, quasi-one-dimensional excitons in a magnetic environment. Despite its pivotal importance for solid-state research, the exciton lifetime has remained unknown. While terahertz polarization probing can directly trace all excitons, independently of interband selection rules, the corresponding large far-field foci substantially exceed the lateral sample dimensions. Here, we combine terahertz polarization spectroscopy with near-field microscopy to reveal a femtosecond decay of paramagnetic excitons in a monolayer of CrSBr, which is 30 times shorter than the bulk lifetime. We unveil low-energy fingerprints of bound and unbound electron–hole pairs in bulk CrSBr and extract the nonequilibrium dielectric function of the monolayer in a model-free manner. Our results demonstrate the first direct access to the ultrafast dielectric response of quasi-one-dimensional excitons in CrSBr, potentially advancing the development of quantum devices based on ultrathin van der Waals magnets.