Nonlocal electrodynamics in Weyl semi-metals

Abstract

Recently synthesized 3D materials with Dirac spectrum exhibit peculiar electric transport qualitatively different from its 2D analogue, graphene. Neglecting impuritiy scattering, the real part of the conductivity is strongly frequency dependent (linear), while the imaginary part is non-zero (unlike in undoped, clean graphene). The Coulomb interaction between electrons is unscreened as in a dielectric and hence is long range. We demonstrate that the interaction correction renders the electrodynamics nonlocal on a mesoscopic\ scale. The longitudinal conductivity $\sigma _{L}$ (related by charge conservation to the electric susceptibility) and the transverse conductivity $\sigma _{T}$ are different in the long wave length limit and consequently the standard local Ohm's law description does not apply. This leads to several remarkable effects in transport and optical response. We predict a charging effect in DC transport that is a direct signature of the nonlocality. The optical response of the WSM is also sensitive to the nonlocality. In these materials p-polarized light generates bulk plasmons as well as the transversal waves. The propagation inside the WSM is only slightly attenuated. At a specific (material parameter dependent) frequency the two modes coincide, a phenomenon impossible in a local medium. Remarkably, for any frequency there is an incident angle where total absorption occurs, turning the WSM opaque.