Strongly Coupled Magnon-Plasmon Polaritons in Graphene-Two-Dimensional Ferromagnet Heterostructures

Magnons and plasmons are different collective modes,involvingthe spin and charge degrees of freedom, respectively. Formation ofhybrid plasmon-magnon polaritons in heterostructures of plasmonicand magnetic systems faces two challenges, the small interaction ofthe electromagnetic field of the plasmon with the spins, and the energymismatch, as in most systems plasmons have energies orders of magnitudelarger than those of magnons. We show that graphene plasmons formpolaritons with the magnons of two-dimensional ferromagnetic insulators,placed up to to half a micrometer apart, with Rabi splittings in therange of 100 GHz (dramatically larger than cavity magnonics). Thisis facilitated both by the small energy of graphene plasmons and thecooperative super-radiant nature of the plasmon-magnon couplingafforded by phase matching. We show that the coupling can be modulatedboth electrically and mechanically, and we propose a ferromagneticresonance experiment implemented with a two-dimensional ferromagnetdriven by graphene plasmons.