Strain-induced chiral magnetic effect in Weyl semimetals

We argue that strain applied to a time-reversal and inversion breaking Weyl semimetal in a magnetic field can induce an electric current via the chiral magnetic effect. A tight-binding model is used to show that strain generically changes the locations in the Brillouin zone but also the energies of the band touching points (tips of the Weyl cones). Since axial charge in a Weyl semimetal can relax via intervalley scattering processes, the induced current will decay with a time scale given by the lifetime of a chiral quasiparticle. We estimate the strength and lifetime of the current for typical material parameters and find that it should be experimentally observable.

Figure 1

Local band structure of a Weyl semimetal with two nodal points at different energies and different positions in momentum space. In (a) there are Fermi surfaces of different sizes for left- and right-handed fermions as measured by the left- and right-handed chemical potentials ${\mu }_{L,R}$. The Fermi energy of both Weyl cones is, however, the same in equilibrium, resulting in vanishing CME. In (b) the situation shortly after applying strain is depicted. The tips of the Weyl cones have shifted in energy but the Fermi surfaces have not yet had enough time time to equilibrate, $t<{\tau }_{\mathrm{inter}}$. The CME is given by $\vec{J}=\frac{\delta {\mu }_5\left(t\right)-\delta b_0}{2{\pi }^2}\vec{B}$. Over a time scale given by the intervalley scattering time ${\tau }_{\mathrm{inter}}$, the axial chemical potential $\delta {\mu }_5$ will build up such that for $t\gg {\tau }_{\mathrm{inter}}$ it takes the value $\delta {\mu }_5=\delta b_0$ and equilibrium with vanishing CME is reached again.