Bulk and surface polaritons in Weyl semimetals*

We report theoretical studies of the optical properties and polariton modes of Type I Weyl semimetals with two Weyl nodes. We present rigorous quantum-mechanical derivation of bulk and surface conductivity tensors including both intraband and interband optical transitions and taking into account all possible combinations of bulk-to-bulk, bulk-to-surface, and surface-to-surface transitions. We show how the information about the electronic structure of Weyl semimetals, such as position and separation of Weyl nodes, Fermi energy, surface states etc. can be unambiguously extracted from their optical response, namely from the reflection, transmission, and polarization change of incident radiation. We predict the optical Hall effect and anomalous dispersion for surface polaritons excited by a nanotip. We show that Weyl semimetals represent a new class of gyrotropic materials with unique electrodynamics due to the combination of strongly anisotropic and gyrotropic bulk conductivity, surface conductivity, and surface dipole layer.