# Do Truly Unidirectional Surface Plasmon-Polaritons Exist?

## TL;DR

This paper investigates the existence of strictly unidirectional surface plasmon-polaritons in nonreciprocal plasmonic structures, revealing that certain configurations can support robust unidirectionality despite nonlocal effects and dissipation.

## Contribution

It clarifies conditions under which truly unidirectional surface plasmon-polaritons can exist, especially at interfaces with opaque isotropic materials, and analyzes their behavior in extreme wave-guiding scenarios.

## Key findings

- Conventional surface magneto-plasmons are not strictly unidirectional due to nonlocal effects.
- Unidirectional surface plasmon-polaritons can exist at interfaces with opaque isotropic materials, maintaining unidirectionality.
- Terminated unidirectional waveguides exhibit counter-intuitive behaviors.

## Abstract

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 magneto-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 preserve their unidirectionality even in the presence of nonlocality, and for arbitrarily-small levels of dissipation. We also investigate the extreme behavior of terminated unidirectional wave-guiding structures, for both classes of surface waves, and discuss their counter-intuitive implications.

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Source: https://tomesphere.com/paper/1904.08392