Effects of non-Hermitian perturbations on Weyl Hamiltonians with arbitrary topological charges

Understanding the properties of non-Hermitian topological systems is of critical importance for photonic and acoustic systems, where it is relatively easy to add material gain and absorption. Here, the authors provide a systematic study of the effects of adding gain and loss to Weyl semimetals, whereby Weyl points with arbitrary charge expand into topologically charged rings of degeneracies. This yields a new class of topological transitions, which occur by changing the strength of the gain and loss, rather than altering the symmetry of the system.