Weyl rings and enhanced susceptibilities in pyrochlore iridates: $k\cdot p$ analysis of cluster dynamical mean-field theory results

We match analytic results to numerical calculations to provide a detailed picture of the metalinsulator and topological transitions found in density functional plus cluster dynamical mean-field calculations of pyrochlore iridates. We discuss the transition from Weyl metal to Weyl semimetal regimes, and then analyse in detail the properties of the Weyl semimetal phase and its evolution into the topologically trivial insulator. The energy scales in the Weyl semimetal phase are found to be very small, as are the anisotropy parameters. The electronic structure can to a good approximation be described as ‘Weyl rings’ and one of the two branches that contributes to the Weyl bands is essentially flat, leading to enhanced susceptibilities. The optical longitudinal and Hall conductivities are determined; the frequency dependence includes pronounced features that reveal the basic energy scales of the Weyl semimetal phase.