Negative refraction in Weyl semimetals

We theoretically propose that Weyl semimetals may exhibit negative refraction at some frequencies close to the plasmon frequency, allowing transverse magnetic (TM) electromagnetic waves with frequencies smaller than the plasmon frequency to propagate in the Weyl semimetals. The idea is justified by the calculation of reflection spectra, in which \textit{negative} refractive index at such frequencies gives physically correct spectra. In this case, a TM electromagnetic wave incident to the surface of the Weyl semimetal will be bent with a negative angle of refraction. We argue that the negative refractive index at the specified frequencies of the electromagnetic wave is required to conserve the energy of the wave, in which the incident energy should propagate away from the point of incidence.