Chiral magnetic effect and natural optical activity in metals with or without Weyl points

A recent experimental identification of mono-pnictides (TaAs, TaP, NbP, and others) as Weyl semimetals has triggered an enormous effort to understand the unconventional physical phenomena in these materials. The chiral magnetic effect (CME), i.e., the occurrence of electrical current along the direction of an applied magnetic field, has been a particularly controversial subject, with a number of claims and counter-claims published in the literature. In this work Jing Ma and D. A. Pesin from the University of Utah provide a systematic theory of the CME and the related natural optical activity in these materials. They show that the natural optical activity of metals can be distinguished from well known phenomena in insulators by its singular frequency dependence in the terahertz range.