Chiral anomaly and optical absorption in Weyl semimetals

Weyl semimetals are a three-dimensional topological phase of matter with isolated band touchings in the Brillouin zone. These points have an associated chirality, and many of the proposals to detect the Weyl semimetal state rely on the chiral anomaly. A consequence of the chiral anomaly is that under the application of an $\mathbf{E}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{B}$ field, charge is transferred between points of opposite chirality. In this paper we propose an optical absorption experiment that provides evidence for the chiral anomaly. We use the Kubo formula, and find that an applied $\mathbf{E}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{B}$ induces the formation of steplike features at finite frequency in the interband optical conductivity. We study the effect of scattering and finite temperatures on this feature and find that it should be observable at low temperatures in pure samples. Finally we discuss how the application of an $\mathbf{E}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{B}$ field can be used to map out the frequency dependence of the scattering rate.