  The study of cavity magnonics and topological insulators has made significant
advances over the past decade, however the possibility of combining the two
fields is still unexplored. Here, we explore such connection by investigating
hybrid cavity systems that incorporate both a ferromagnet and a topological
insulator. We find that electrons in the topological surface state efficiently
mediate the effective electric dipole coupling between the spin of the
ferromagnet and the electric field of the cavity, in contrast with the
conventional cavity magnonics theory based on magnetic dipole coupling. We
refer to this coupling as topological magnon-photon interaction, estimating it
one order of magnitude stronger than the conventional magnon-photon coupling,
and showing that its sign can be manipulated. We discuss the potential of our
proposed device to allow for scaling down and controlling the cavity system
using electronics. Our results provide solid ground for exploring the
functionalities enabled by merging cavity magnonics with topological
insulators.
