Surface plasmon polaritons in topological Weyl semimetals

We consider theoretically surface plasmon polaritons in Weyl semimetals. These materials contain pairs of band touching points—Weyl nodes—with a chiral topological charge, which induces an optical anisotropy and anomalous transport through the chiral anomaly. We show that these effects, which are not present in ordinary metals, have a direct fundamental manifestation in the surface plasmon dispersion. The retarded Weyl surface plasmon dispersion depends on the separation of the Weyl nodes in energy and momentum space. For Weyl semimetals with broken time-reversal symmetry, the distance between the nodes acts as an effective applied magnetic field in momentum space, and the Weyl surface plasmon polariton dispersion is strikingly similar to magnetoplasmons in ordinary metals. In particular, this implies the existence of nonreciprocal surface modes. In addition, we obtain the nonretarded Weyl magnetoplasmon modes, which acquire an additional longitudinal magnetic field dependence. These predicted surface plasmon results are observable manifestations of the chiral anomaly in Weyl semimetals and might have technological applications.

Figure 1

Surface plasmon dispersion of a Weyl semimetal with broken time-reversal symmetry for different values of (top to bottom) (a) ${\omega }_b/{\mathrm{\Omega }}_p=0.25$, 0.5, 0.75, and 1; (b) $0.5$, 1, and $1.5$; and (c) $0.5$. In (c), the continuous blue line denotes positive wave numbers $q>0$ and the dotted blue line $q<0$. In all plots, the bulk plasmon dispersion is indicated by thin red lines. The thin black lines denote the asymptotic light line and the nonretarded frequency, respectively, and the black dashed line indicates the SPP dispersion of a standard Dirac material. As discussed in the main text, the black dots mark the points where the SPP hybridizes with the bulk plasmon mode and is damped.

Figure 2

Surface plasmon dispersion of a Weyl semimetal with broken inversion symmetry for ${\omega }_{b_0}/{\mathrm{\Omega }}_p=0.5$ and 1. The notation is the same as in Fig. 1.