Unidirectional bulk magnetoplasmons at terahertz frequencies

Unidirectional electromagnetic modes, as an extreme regime of wave propagation, enable extraordinary and counterintuitive optical effects. These modes are typically realized as tightly confined surface waves in photonic crystals or materials with topologically nontrivial bandgaps. Here, we show that a structure comprising a magnetized semiconductor layer sandwiched between electro- and magneto-opaque materials can support unidirectional bulk magnetoplasmons at terahertz frequencies, in which all field components maintain constant amplitudes within the core layer. These modes exhibit modal properties that are independent of the core thickness, allowing the modal spot to extend over several wavelengths. Numerical simulations further confirm their immunity to backscattering. By combining the tunability of modal spot with the robustness of unidirectional propagation, these unidirectional bulk modes offer more degrees of freedom for the manipulation of terahertz waves.