Anisotropic Propagation of Magnetically Dressed Exciton Polaritons in van der Waals Antiferromagnets

Exciton-polaritons, formed through the strong coupling between excitons and photons, offer particular interest in photonics, optoelectronics, and quantum information applications. Recently, a new class of air-stable van der Waals (vdW) antiferromagnet CrSBr has gained significant attention due to its ability to form self-hybridize magnetically dressed exciton-polariton (MEP) states without the need for an external waveguide cavity. Studies show the MEPs in CrSBr can also be characterized as hyperbolic exciton-polaritons (HEPs) with anisotropic propagation along different crystal axes. To further investigate these novel HEP states, we use atomic force microscope (AFM) to create nanoindents that enable out coupling of MEPs for far-field photoluminance(PL) spectroscopy measurements. We observe that MEPs with energy higher than 1.34eV propagate exclusively along the crystalline b-axis, while magnetically dressed exciton-phonon bound (MEPB) states propagate isotopically along both the crystalline a- and b- axes. Additionally, we find interesting temperature- and thickness- dependent propagation of MEP and MEPB states. The ability to optically read out MEP coupling in CrSBr has significant implications for designing light-matter interactions in magnetic semiconductors. Moreover, it provides a promising platform for developing reconfigurable on-chip waveguides for quantum information transport.