Magnetic impurities in three-dimensional Dirac and Weyl systems are shown to
exhibit a fascinatingly diverse range of Kondo physics, with distinctive
experimental spectroscopic signatures. When the Fermi level is precisely at the
Dirac point, Dirac semimetals are in fact unlikely candidates for a Kondo
effect due to the pseudogapped density of states. However, the influence of a
nearby quantum critical point leads to the unconventional evolution of Kondo
physics for even tiny deviations in the chemical potential. Separating the
degenerate Dirac nodes produces a Weyl phase: time-reversal symmetry-breaking
precludes Kondo due to an effective impurity magnetic field, but different
Kondo variants are accessible in time-reversal invariant Weyl systems.Comment: 4+ pages, 2 figure