Signatures of the Chiral Anomaly in Phonon Dynamics

Discovered in high-energy physics, the chiral anomaly has recently made way to materials science by virtue of Weyl semimetals (WSM). Thus far, the main efforts to probe the chiral anomaly in WSM have concentrated on electronic phenomena. Here, we show that the chiral anomaly can have a large impact in the $A_1$ phonons of enantiomorphic WSM. In these materials, the chiral anomaly produces an unusual magnetic-field-induced resonance in the effective phonon charge, which in turn leads to anomalies in the phonon dispersion, optical reflectivity, and the Raman scattering.

Figure 1

Anomaly induced coupling between an IR inactive optical phonon and a linearly dispersing pseudoscalar boson in presence of a static and uniform magnetic field ${\mathbf{B}}_0$, with $\widehat{\mathbf{q}}·{\mathbf{B}}_0=-1T$ (see Ref. [23] for plots with other values of $\widehat{\mathbf{q}}·{\mathbf{B}}_0$). The curves are solutions to Eq. (14), with parameter values taken from Ref. [23]. When $|\mathbf{q}|\lesssim {\omega }_0/v$, the linear mode is doubly degenerate but one solution is unstable (antidamped). A large static dielectric constant is assumed so that Landau damping at $q_0>v|\mathbf{q}|$ can be neglected.