2D CrSBr Enables Magnetically Controllable Exciton-Polaritons in an Open Cavity

2D van der Waals (vdW) layered materials exhibit significant exciton binding energy and versatile stacking options, making them ideal for room-temperature exciton-polariton devices used in low-threshold lasing, nonlinear optical switching, and quantum computing. However, most existing systems depend on external optical microcavities coupled with single monolayers, leading to limited controllability and increased costs. Here, external cavity-free vdW magnet CrSBr crystals are presented that feature magnetically controllable self-hybridized exciton-polaritons that remain stable up to room temperature. The ultrastrong exciton-photon coupling suppresses donor-, phonon-, and defect-related emissions. Furthermore, the exciton-polariton dispersion and emission spectra can be effectively controlled by adjusting the magnetic field, temperature, and CrSBr thickness. This vdW exciton-polariton material platform, demonstrating remarkable magnetic responsiveness in open cavity configurations under ambient conditions, paves the way for the development of compact, fast, and low-loss spin, quantum, and magneto-photonic devices.