Sub-millimeter propagation of antiferromagnetic magnons via magnon-photon coupling

Abstract: For the realization of magnon-based current-free technologies, referred to as magnonics, all-optical control of magnons is an important technique for both fundamental research and practical applications. Magnon-polariton is a coupled state of magnon and photon in a magnetic medium, expected to exhibit magnon-like controllability and photon-like high-speed propagation. While recent studies have observed magnon-polaritons as modulation of incident terahertz waves, the influence of magnon-photon coupling on magnon propagation properties remains unexplored. This study aimed to observe the spatiotemporal dynamics of coherent magnon-polaritons through time-resolved imaging measurements. BiFeO$_3$ was selected as the sample due to its anticipated strong coupling between magnons and photons. The observed dynamics suggest that antiferromagnetic magnons can propagate over long distances, up to hundreds of micrometers, through strong coupling with photons. These results enhance our understanding of the optical control of magnonic systems, thereby paving the way for terahertz opto-magnonics.