Phonon-mediated strong coupling between a three-dimensional topological insulator and a two-dimensional antiferromagnetic material

We numerically study strong coupling between terahertz excitations in a hybrid material consisting of a three-dimensional (3D) topological insulator (TI) and a quasi-two-dimensional (2D) van der Waals antiferromagnet. We find that the interaction between a surface Dirac plasmon polariton in the 3D TI and a magnon polariton in the 2D antiferromagnet is mediated by the phonon coupling in the 3D TI material and can result in emergence of a new hybridized mode, namely, a surface Dirac plasmon-phonon-magnon polariton. We numerically study the dependence of the strong coupling on a variety of structural parameters of the 3D-TI/2D-antiferromagnetic (AFM) hybrid material. Our results reveal that the strength of the coupling depends primarily on the anisotropy constant of the 2D AFM material, as well as on its thickness, and reaches a maximum when the AFM layer is sufficiently thick to be considered a half-infinite slab. We show that the extremely large anisotropy constant reported for certain 2D van der Waals antiferromagnets results in a coupling strength that should be experimentally observable even in the presence of realistic scattering losses.