Tunable Magneto-Excitonic Coupling in Alloyed van der Waals Antiferromagnet

Maciej Smiertka; Oliwia Janikowska; Katarzyna Olkowska-Pucko; Grzegorz Krasucki; Katarzyna Posmyk; Paulina Peksa; Alessandro Surrente; Dimitar Pashov; Kseniia Mosina; Zdenek Sofer; Mark van Schilfgaarde; Adam Babinski; Maciej R. Molas; Gabriela Komorowska; Esteban Zamora-Amo; Andres Castellanos-Gomez; Federico Mompean; Mar Garcia-Hernandez; Michal Baranowski; Swagata Acharya; Paulina Plochocka

arXiv · 2607.14723

Tunable Magneto-Excitonic Coupling in Alloyed van der Waals Antiferromagnet

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Abstract

The unique coupling between magnetic order and photo-generated excitons, electron-hole pairs bound by Coulomb interaction, in layered magnetic semiconductors offers a powerful mechanism for controlling light-matter interactions. In the van der Waals antiferromagnet CrSBr, this coupling is exceptionally strong and manifests distinctly between two coexisting excitonic states: the localised, Frenkel-like XA exciton and the more delocalised, Wannier-Mott-like XB exciton, providing a unique playground for the optical control of magnetism. Here, we reveal how chlorine incorporation reshapes the magneto-optical interplay in CrSBr1-xClx by simultaneously modifying its electronic structure, excitonic properties, and magnetic interactions. Combining magneto-optical spectroscopy up to 85 T with state-of-the-art quasiparticle self-consistent GW (QSGW) calculations on alloy supercells, we show that Cl insertion progressively localises the excitonic wavefunctions and drives both states toward a more Frenkel-like regime. This evolution is accompanied by a systematic reduction of the magnetic-field-induced energy renormalisation, most prominently for the XB exciton. Our work connects exciton character directly to magneto-excitonic coupling. Furthermore, it establishes compositional alloying as an effective strategy for engineering the coupling between magnetic and optical properties in van der Waals magnetic semiconductors.

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Maciej Smiertka, Oliwia Janikowska, Katarzyna Olkowska-Pucko, Grzegorz Krasucki, Katarzyna Posmyk, Paulina Peksa, Alessandro Surrente, Dimitar Pashov, Kseniia Mosina, Zdenek Sofer, Mark van Schilfgaarde, Adam Babinski, Maciej R. Molas, Gabriela Komorowska, Esteban Zamora-Amo, Andres Castellanos-Gomez, Federico Mompean, Mar Garcia-Hernandez, Michal Baranowski, Swagata Acharya, Paulina Plochocka. 2026-07-16. Tunable Magneto-Excitonic Coupling in Alloyed van der Waals Antiferromagnet. https://arxiv.org/abs/2607.14723

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