  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 an 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.
