Understanding the charge pumping and relaxation of the chiral anomaly in a Dirac semimetal

The 3D Dirac and Weyl semimetals can be characterized by a charge chirality with the parallel or antiparallel locking of electron spin in its momentum. Such materials can exhibit a chiral magnetic effect associated with the near conservation of chiral charge. In this work, Bing Cheng and a research team in physics and astronomy at the Johns Hopkins University and materials science at the University of California, Santa Barbara, used magneto-terahertz spectroscopy to study epitaxial cadmium arsenide (Cd3As2) films—a widely explored material in solid-state physics to extract their conductivities as a function of chiral magnetic effect . When the team applied the field, they noted a markedly sharp Drude response – a highly acclaimed model of electronic transport suggested by physicist Paul Drude more than 100 years ago. The Drude response rose out of the broader background of this system as a definitive signature of a new transport channel consistent with the chiral response. The field independence of the chiral relaxation established that it was set by the approximate conservation of the isospin in the setup.