Broadband unidirectional electromagnetic mode at interface of anti-parallel magnetized media

We report a kind of broadband electromagnetic boundary mode at an interface of anti-parallel magnetized media, which can only propagate in one direction perpendicular to the magnetization and parallel to the interface. The unidirectionality of this mode originates from the permeability or permittivity tensor introduced by magnetization. We theoretically and numerically analyze the existence of the unidirectional mode, and point out that this mode can exist in both gyromagnetic and gyroelectric medium. We also propose a one-way waveguide based on this unidirectional mode, which may realize a new kind of electromagnetic isolation differing from those existing ones.