Title: Weyl Rings and enhanced susceptibilities in Pyrochlore Iridates: $k\cdot p$ Analysis of Cluster Dynamical Mean-Field Theory Results,
Abstract: We match analytic results to numerical calculations to provide a detailed
picture of the metal-insulator 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.