Magnetic Polaronic Exciton in A-Type 2D van der Waals Bulk Material CrSBr

Abstract

Two-dimensional van der Waals magnetic semiconductors offer unprecedented opportunities to explore coupled magnetic and excitonic phenomena. Through femtosecond transient absorption spectroscopy and density functional theory calculations, we identify the charge-transfer band edge in CrSBr near 500 nm (2.48 eV) and correlate distinct photoluminescence (PL) channels with Cr³⁺ coordination environments. Temperature-dependent measurements reveal that 720 nm emission (PL₁) persists across all temperatures, consistent with isolated Cr³⁺ centers; ∼920 nm emission (PL₂) intensifies near the ferromagnetic (FM) transition (140 K); and 990 nm emission (PL₃) appears only in thick samples below the antiferromagnetic (AFM) transition (132 K). Under strong perpendicular magnetic fields with 488 nm excitation, we observe a dark-state exciton at ∼850 nm, with anticorrelated intensity variations between PL₁/dark-state and PL₂/PL₃, demonstrating field-tuned energy redistribution. These findings establish magnetic polaronic excitons in van der Waals semiconductors and enable manipulation of excitonic properties through magnetic order control.

Keywords

antiferromagnet / charge-transfer band edge / CrSBr / dark exciton / magnetic polaronic exciton

References

[1] C. Gong, L. Li, Z. Li, et al., “Discovery of Intrinsic Ferromagnetism in Two-Dimensional van der Waals Crystals,” Nature 546 (2017): 265-269.

[2] B. Huang, G. Clark, E. Navarro-Moratalla, et al., “Layer-Dependent Ferromagnetism in a van der Waals Crystal Down to the Monolayer Limit,” Nature 546 (2017): 270-273.

[3] B. Huang, M. A. McGuire, A. F. May, D. Xiao, P. Jarillo-Herrero, and X. Xu, “Emergent Phenomena and Proximity Effects in Two-Dimensional Magnets and Heterostructures,” Nature Materials 19 (2020): 1276-1289.

[4] H. Li, S. Ruan, and Y. J. Zeng, “Intrinsic van der Waals Magnetic Materials From Bulk to the 2D Limit: New Frontiers of Spintronics,” Advanced Materials 31 (2019): 1900065.

[5] M. Gibertini, M. Koperski, A. F. Morpurgo, and K. S. Novoselov, “Magnetic 2D Materials and Heterostructures,” Nature Nanotechnology 14 (2019): 408-419.

[6] E. J. Telford, A. H. Dismukes, K. Lee, et al., “Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van Der Waals Semiconductor CrSBr,” Advanced Materials 32 (2020): 2003240.

[7] M. E. Ziebel, M. L. Feuer, J. Cox, X. Zhu, C. R. Dean, and X. Roy, “CrSBr: An Air-Stable, Two-Dimensional Magnetic Semiconductor,” Nano Letters 24 (2024): 4319-4329.

[8] S. A. López-Paz, Z. Guguchia, V. Y. Pomjakushin, et al., “Dynamic Magnetic Crossover in CrSBr,” Nature Communications 13 (2022): 4745.

[9] J. Beck, “Über Chalkogenidhalogenide des Chroms Synthese, Kristallstruktur und Magnetismus von Chromsulfidbromid, CrSBr,” Zeitschrift für Anorganische und Allgemeine Chemie 585 (1990): 157-167.

[10] O. Göser, W. Paul, and H. G. Kahle, “Magnetic Properties of CrSBr,” Journal of Magnetism and Magnetic Materials 92 (1990): 129-136.

[11] K. Lee, A. H. Dismukes, E. J. Telford, et al., “Magnetic Order and Symmetry in the 2D Semiconductor CrSBr,” Nano Letters 21 (2021): 3511-3517.

[12] N. P. Wilson, K. Lee, J. Cenker, et al., “Interlayer Electronic Coupling on Demand in a 2D Magnetic Semiconductor,” Nature Materials 20 (2021): 1657-1662.

[13] M. A. Tschudin, D. A. Broadway, P. Siegwolf, et al., “Imaging Nanomagnetism and Magnetic Phase Transitions in Atomically Thin CrSBr,” Nature Communications 15 (2024): 6005.

[14] D. Shcherbakov, P. Stepanov, D. Weber, et al., “Raman Spectroscopy, Photocatalytic Degradation, and Stabilization of Atomically Thin Chromium Tri-Iodide,” Nano Letters 18 (2018): 4214-4219.

[15] E. J. Telford, A. H. Dismukes, R. L. Dudley, et al., “Coupling Between Magnetic Order and Charge Transport in a Two-Dimensional Magnetic Semiconductor,” Nature Materials 21 (2022): 754-760.

[16] F. Tabataba-Vakili, H. P. Nguyen, A. Rupp, et al., “Doping-Control of Excitons and Magnetism in Few-Layer CrSBr,” Nature Communications 15 (2024): 4735.

[17] F. Dirnberger, J. Quan, R. Bushati, et al., “Magneto-Optics in a van der Waals Magnet Tuned by Self-Hybridized Polaritons,” Nature 620 (2023): 533-537.

[18] Y. J. Bae, J. Wang, A. Scheie, et al., “Exciton-Coupled Coherent Magnons in a 2D Semiconductor,” Nature 609 (2022): 282-286.

[19] G. M. Diederich, J. Cenker, Y. Ren, et al., “Tunable Interaction Between Excitons and Hybridized Magnons in a Layered Semiconductor,” Nature Nanotechnology 18 (2023): 23-28.

[20] F. L. Ruta, S. Zhang, Y. Shao, et al., “Hyperbolic Exciton Polaritons in a van der Waals Magnet,” Nature Communications 14 (2023): 8261.

[21] K. Lin, X. Sun, F. Dirnberger, et al., “Strong Exciton-Phonon Coupling as a Fingerprint of Magnetic Ordering in van der Waals Layered CrSBr,” ACS Nano 18 (2024): 2898-2905.

[22] F. Marques-Moros, C. Boix-Constant, S. Mañas-Valero, J. Canet-Ferrer, and E. Coronado, “Interplay Between Optical Emission and Magnetism in the van der Waals Magnetic Semiconductor CrSBr in the Two-Dimensional Limit,” ACS Nano 17 (2023): 13224-13231.

[23] M. Liebich, M. Florian, N. Nilforoushan, et al., “Controlling Coulomb Correlations and Fine Structure of Quasi-One-Dimensional Excitons by Magnetic Order,” Nature Materials 24 (2025): 384-390.

[24] Y. Shao, F. Dirnberger, S. Qiu, et al., “Magnetically Confined Surface and Bulk Excitons in a Layered Antiferromagnet,” Nature Materials 24 (2025): 391-398.

[25] B. Datta, P. C. Adak, S. Yu, et al., “Magnon-Mediated Exciton-Exciton Interaction in a van der Waals Antiferromagnet,” Nature Materials 24 (2025): 1027-1033.

[26] M. A. Semina, F. Tabataba-Vakili, A. Rupp, A. S. Baimuratov, A. Högele, and M. M. Glazov, “Excitons and Trions in CrSBr Bilayers,” Physical Review B 111 (2025): 205301.

[27] X. Wu, J. Chen, M. Gu, et al., “Magnetic Order Dependent Photoluminescence From High Energy Excitons in hBN Protected Few-Layer CrSBr,” preprint, arXiv:2507.23301, July 31, 2025.

[28] J. Klein, B. Pingault, M. Florian, et al., “The Bulk van der Waals Layered Magnet CrSBr is a Quasi-1D Material,” ACS Nano 17 (2023): 5316-5328.

[29] M. C. Heißenbüttel, P. M. Piel, J. Klein, T. Deilmann, U. Wurstbauer, and M. Rohlfing, “Dielectric Properties of CrSBr,” Physical Review B 111 (2025): 075107.

[30] T. Wang, D. Zhang, S. Yang, et al., “Magnetically-Dressed CrSBr Exciton-Polaritons in Ultrastrong Coupling Regime,” Nature Communications 14 (2023): 5966.

[31] J. Sears, B. Zager, W. He, et al., “Observation of Anisotropic Dispersive Dark-Exciton Dynamics in CrSBr,” Physical Review Letters 135 (2025): 146503.

[32] C. Meineke, J. Schlosser, M. Zizlsperger, et al., “Ultrafast Exciton Dynamics in the Atomically Thin van der Waals Magnet CrSBr,” Nano Letters 24 (2024): 4101-4107.

[33] S. Bork, R. Leven, V. Wirsdörfer, et al., “Magnetic Order Unlocks Optical Access to Dark Excitons in CrSBr,” preprint, arXiv:2511.20268, November 25, 2025.

[34] R. Komar, A. Łopion, M. Goryca, et al., “Colossal Magneto-Excitonic Effects in 2D van der Waals Magnetic Semiconductor CrSBr,” preprint, arXiv:2409.00187, September 1, 2024.

[35] Y. Song, P. Gu, Y. Gao, et al., “Subnanometer-Scale Probing of Excitonic Behavior in 2D Semiconductor CrSBr,” Nano Letters 25 (2025): 11655-11662.

[36] V. Porée, A. Zobelli, A. Pawbake, et al., “Electronic Structure of CrSBr,” Physical Review B 112 (2025): 125103.

[37] W. Linhart, M. Rybak, M. Birowska, et al., “Optical Markers of Magnetic Phase Transition in CrSBr,” Journal of Materials Chemistry C 11 (2023): 8423-8430.

[38] D. L. Esteras, A. Rybakov, A. M. Ruiz, and J. J. Baldoví, “Magnon Straintronics in the 2D van der Waals Ferromagnet CrSBr From First-Principles,” Nano Letters 22 (2022): 8771-8778.

[39] D. F. Nelson and M. D. Sturge, “Relation Between Absorption and Emission in the Region of the R Lines of Ruby,” Physical Review 137 (1964): A1117-A1130.

[40] S. Smolenski, M. Wen, Q. Li, et al., “Large Exciton Binding Energy in a Bulk van der Waals Magnet From Quasi-1D Electronic Localization,” Nature Communications 16 (2025): 1134.

[41] J. Heber, C. Gmachl, H. Ng, and A. Cho, “Comparative Study of Ultrafast Intersubband Electron Scattering Times at ∼1.55µm Wavelength in GaN/AlGaN Heterostructures,” Applied Physics Letters 81 (2002): 1237-1239.

[42] G. Fasol, W. Hackenberg, H. Hughes, K. Ploog, E. Bauser, and H. Kano, “Continuous-Wave Spectroscopy of Femtosecond Carrier Scattering in GaAs,” Physical Review B 41 (1990): 1461-1478.

[43] E. Fill, L. Veisz, A. Apolonski, and F. Krausz, “Sub-fs Electron Pulses for Ultrafast Electron Diffraction,” New Journal of Physics 8 (2006): 272-282.

[44] B. Rethfeld, A. Kaiser, M. Vicanek, and G. Simon, “Ultrafast Dynamics of Nonequilibrium Electrons in Metals Under Femtosecond Laser Irradiation,” Physical Review B 65 (2002): 214303.

[45] Y. Li, G. Liang, C. Kong, B. Sun, and X. Zhang, “Charge-Transfer-Mediated Exciton Dynamics in Van der Waals Antiferromagnet NiPS 3,” Advanced Functional Materials 34 (2024): 2402161.

[46] K. L. Seyler, D. Zhong, D. R. Klein, et al., “Ligand-Field Helical Luminescence in a 2D Ferromagnetic Insulator,” Nature Physics 14 (2018): 277-281.

[47] L. Nessi, C. A. Occhialini, A. K. Demir, L. Powalla, and R. Comin, “Magnetic Field Tunable Polaritons in the Ultrastrong Coupling Regime in CrSBr,” ACS Nano 18 (2024): 34235-34243.

[48] J. Shi, D. Wang, N. Jiang, et al., “Giant Magneto-Exciton Coupling in 2D van der Waals CrSBr,” ACS Nano 19 (2025): 29977-29987.

[49] M. Smiertka, M. Rygala, K. Posmyk, et al., “Distinct magneto-optical response of Frenkel and Wannier excitons in CrSBr,” Nature Communications 17 (2026): 1777.

[50] R. Liu, L. Shi, and B. Zou, “Magnetic Exciton Relaxation and Spin-Spin Interaction by the Time-Delayed Photoluminescence Spectra of ZnO: Mn Nanowires,” ACS Applied Materials and Interfaces 6 (2014): 10353-10366.

[51] J. I. Pankove, Optical Processes in Semiconductors (Courier Corporation, 1975).

[52] A. Pawbake, T. Pelini, N. P. Wilson, et al., “Raman Scattering Signatures of Strong Spin-Phonon Coupling in the Bulk Magnetic van der Waals Material CrSBr,” Physical Review B 107 (2023): 075421.

[53] H. Cheng, J. Zhou, C. Hu, et al., “Magnetic Sensitive Mechanical Response in CrSBr and Its Composite Resonators,” Applied Physics Letters 125 (2024): 183101.

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2026 The Author(s). Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.