Robust Unidirectional Surface Plasmon-Polaritons at Visible Frequencies Under Normal Magnetic Field

Truly unidirectional surface plasmon-polaritons (USPPs) were recently confirmed to exist in a magnetized semiconductor interfaced with an opaque isotropic medium in its topologically nontrivial bandgap at terahertz frequencies. In this work, surface waves at an interface between a gyroelectric material and an opaque medium for general case are theoretically investigated, and the conditions for existence of robust unidirectional modes, which lie in the topologically nontrivial bandgap of the gyroelectric material, are analytically derived. Additionally, in visible regime, a layered plasmonic-gyroelectric metamaterial with topologically nontrivial bandgap is developed under normal external magnetic field. Based on this metamaterial, robust USPPs at visible frequencies are achieved at an interface with an opaque material with proper (negative) permittivity. Such visible USPPs are also verified by numerical simulations in a realistic material configuration.