Weyl exceptional rings in a lossy magnetically biased plasma*

Weyl exceptional rings are closed contours in momentum space along which both energy eigenvalues and eigenvectors of a system coalesce. These rings emerge in Weyl semimetals subject to non-Hermitian perturbations. We report the existence of Weyl exceptional rings in the electromagnetic dispersion of a lossy plasma in the presence of an external magnetic field. We describe the conditions under which topologically protected surface states can be preserved or destroyed by changing losses in the system. Increasing losses changes the size of the exceptional rings and anisotropic losses at certain angles relative to the external magnetic field can cause two rings of opposite charge to annihilate each other. This system offers a window to study the rich physics of exceptional rings in a range of plasmonic materials including the optical response of magnetically biased metals and semiconductors.