The chiral anomaly is a purely quantum mechanical phenomenon that has a long history dating back to the late 1960s. Surprisingly, it has recently made a macroscopic appearance in condensed matter physics. A brief introduction to the relevant features of this anomaly is given and it is shown that its appearance in condensed matter systems must involve force-free magnetic fields, which may help explain the long current relaxation times in Dirac and Weyl semimetals.
http://arxiv.org/abs/1605.09214
Canadian Journal of Physics: Published on the web 13 March 2017, 10.1139/cjp
The published version is available here:
THE CHIRAL ANOMALY, DIRAC AND WEYL SEMIMETALS, AND FORCE-FREE MAGNETIC FIELDS