One exciting application of magnetic materials is the use of coherent magnonsas energy-efficient information carriers in spintronicsand magnonicsor as interconnects in hybrid quantum systems. A particular opportunity arises when the magnet is also a semiconductor that features both tightly-bound excitonswith large oscillator strength and potentially long-lived coherent magnonsdue to the bandgap and spatial confinement. While magnonsand excitonsare energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. Here we show strong magnon-excitoncoupling in the A-type antiferromagnetic semiconductor CrSBr. Coherent magnonslaunched by above-gap excitation modulate the excitonenergies. Time-resolved excitonsensing reveals magnonsthat can coherently travel beyond 7 μm, with coherence time above 5 ns.We observe this exciton-coupled coherent magnonsin both even and odd number of layers, with and without compensated magnetization, down to the bilayer limit. Given the versatility of vdWheterostructures, these coherent magnonsmay be basis for optically accessible spintronics, magnonics, and quantum interconnects.
