Dirnberger, Florian
Date: Thursday, October 12, 2023
Time: 11:00
Place: ETH Campus Hönggerberg, HIT F 12
Host: Atac Imamoglu
Magnetic excitons and strong light-matter coupling in van der Waals magnets
Florian Dirnberger – Technische Universität Dresden, Germany
Abstract: Recent studies of van der Waals magnetic crystals spotlight magnetic excitons – a rare type of optical excitation formed by spin-polarized electronic states in magnets. With properties that have no analog amongst excitons in conventional band semiconductors, these optical quasiparticles not only inherit significant potential for optoelectronic devices with new functionalities, they are an excellent platform for the observation of novel interactions between magnetism and light [1].
In this talk, I will introduce two different van der Waals magnets and discuss the coupling of their magnetic excitons to light. One of these materials is NiPS3, an antiferromagnet from the family of Mott insulators with highly correlated magnetic and electronic degrees of freedom. A detailed spectroscopic analysis of its magnetic exciton-polaritons in conjunction with a microscopic theory shows that the origin and behavior of magnetically coupled optical excitations can be very different from that of excitons in conventional band semiconductors [1]. In the second part of the talk, I will discuss the optical and magneto-optical properties of the van der Waals semiconductor CrSBr, an archetypal layered magnet and an exceptional model system for the study of magnetic excitons. Our experiments demonstrate the elemental role of strong light-matter coupling in this material [2]. The hybridization of excitons and photons in crystals both with and without external cavity mirrors is shown to become important when the thickness of this material exceeds more than just a few layers. In this case, signatures of polaritons dominate the optical spectrum, which facilitates control over the magneto-optical properties of this material. We show strong optical responses of polaritons to applied magnetic fields, optically induced coherent magnons, and the excitation of incoherent magnons – a previously unobserved magneto-optical correlation effect in CrSBr. These results highlight novel directions for controlling magneto-optic responses and the manipulation of quantum material properties by strong light-matter coupling.
References
[1] F. Dirnberger, R. Bushati, B. Datta, A. Kumar, A. H. MacDonald, E. Baldini, V. M. Menon, Spin-correlated exciton-polaritons in a van der Waals magnet, Nature Nanotechnology, 17, 1060–1064 (2022)
[2] F. Dirnberger, J. Quan, R. Bushati, G. Diederich, M. Florian, J. Klein, K. Mosina, Z. Sofer, X. Xu, A. Kamra, F. J. García-Vidal, A. Alù, and V. M. Menon, Magneto-optics in a van der Waals magnet tuned by self-hybridized polaritons, Nature 620, 533-537 (2023)