Do truly unidirectional surface plasmon-polaritons exist?

In this work, we revisit the topic of surface waves on nonreciprocal plasmonic structures, and clarify whether strictly unidirectional surface plasmon-polaritons are allowed to exist in this material platform. By investigating different three-dimensional configurations and frequency regimes, we theoretically show that, while conventional surface magne-to-plasmons are not strictly unidirectional due to nonlocal effects, consistent with recent predictions made in the literature, another important class of one-way surface plasmon-polaritons, existing at an interface with an opaque isotropic material, robustly preserves their unidirectionality even in the presence of nonlocality, and for arbitrarily small levels of dissipation. We also investigate the extreme behavior of terminated unidirectional waveguiding structures, for both classes of surface waves, and discuss their counterintuitive implications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement