Tunable surface plasmon polaritons in a Weyl semimetal waveguide.

Weyl semimetals have recently attracted extensive attention due to their anomalous band structure manifested by topological properties that lead to some unusual and unique physical properties. We investigate novel features of surface plasmon polaritons in a slot waveguide comprised from two semi-infinite Weyl semimetals. We consider symmetric Voigt-Voigt and Faraday-Faraday configurations for plasmon polaritons in two interfaces of waveguide and show that the resulting dispersion is symmetric and the propagation of surface plasmon polaritons is bidirectional. We introduce exotic and novel asymmetric structures making use of difference in magnitude or orientation of chiral anomalies in two Weyl semimetals in both Voigt and Faraday configurations. These structures show a tremendous nonreciprocal dispersion and unidirectional propagation of surface plasmon polaritons. Moreover, we study a hybrid configuration of Voigt-Faraday for surface plasmon polartions in two interfaces of the waveguide. We find that this structure possesses unique futures. It shows surface plasmon polariton modes with unidirectional propagation above the bulk plasmon frequency. Furthermore, we find a surface plasmon polariton band which admits the Voigt and Faraday features simultaneously. Also, we show that the waveguide thickness and the chemical potential of the Weyl semimetals can be used as a fine-tuning parameters in these structures. Our findings may be employed in optical devices which exploit the unidirectional surface plasmon propagation features.