Line waves at the interface of magneto–electric boundaries

Line waves (LWs) are a unique class of electromagnetic modes confined to the interface between impedance surfaces, governed by electromagnetic duality. To date, most realizations of LWs have relied exclusively on electric impedance surfaces. In this work, we demonstrate that a planar interface between an electric impedance surface and a purely magnetic medium can support backscattering-immune LWs. The magnetic medium ( \(ε = 1, \, μ ≠ 1\) ) sustains TE-polarized surface magnon polaritons (SMPs), while the electric impedance surface supports TM-polarized surface waves. The coupling of these orthogonally polarized modes gives rise to a one dimensional, pseudospin filtered propagation channel. A comprehensive theoretical framework, supported by full-wave simulations, is developed to analyze dispersion characteristics, field confinement, and spin-momentum locking. The proposed structure enables ultra-confined wave guiding and offers a new platform for manipulating light matter interactions at terahertz frequencies. These findings open new avenues for magneto–electric waveguides and pseudospin-controlled photonic devices.