Strongly direction-dependent magnetoplasmons in mixed Faraday-Voigt configurations

The electrostatic theory of magnetoplasmons on a semi-infinite magnetized electron gas is generalized to mixed Faraday-Voigt configurations. We analyze a new type of electrostatic surface waves that is strongly direction-dependent, and may be realized on narrow-gap semiconductors in the THz regime. A general expression for the dispersion relation is presented, with its dependence on the magnitude and orientation of the applied magnetic field. Remarkably, the group velocity is always perpendicular to the phase velocity. Both velocity and energy relations of the found magnetoplasmons are discussed in detail. In the appropriate limits the known magnetoplasmons in the higher-symmetry Faraday and Voigt configurations are recovered.