Chiral Anomaly and Giant Magnetochiral Anisotropy in Noncentrosymmetric Weyl Semimetals

We theoretically propose that giant magnetochiral anisotropy is achieved in Weyl semimetals in noncentrosymmetric crystals as a consequence of the chiral anomaly. The magnetochiral anisotropy is the nonlinearity of the resistivity $\rho$ that depends on the current $\mathit{I}$ and the magnetic field $\mathit{B}$ as $\rho ={\rho }_0(1+\gamma \mathit{I}·\mathit{B})$, and can be applied to rectifier devices controlled by $\mathit{B}$. We derive the formula for the coefficient $\gamma$ in noncentrosymmetric Weyl semimetals. The obtained formula for $\gamma$ shows that the magnetochiral anisotropy is strongly enhanced when the chemical potential is tuned to Weyl points, and that noncentrosymmetric Weyl semimetals such as TaAs can exhibit much larger magnetochiral anisotropy than that observed in other materials so far.

Figure 1

Schematic picture of Weyl fermions in noncentrosymmetric system. Time-reversal symmetry connects the flow of the Berry curvature $\mathit{b}(\mathit{k})$ at $\mathit{k}$ to that at $-\mathit{k}$ as $\mathit{b}(-\mathit{k})=-\mathit{b}(\mathit{k})$. This means that the Weyl fermions at $\mathit{k}$ and $-\mathit{k}$ have the same chirality; i.e., both are monopoles or antimonopoles. Therefore, there must be at least four Weyl fermions in noncentrosymmetric Weyl semimetals with time-reversal symmetry, i.e., two pairs of WFs and anti-WFs, respectively. When both the magnetic ($\mathit{B}$) and electric ($\mathit{E}$) fields are applied, the charge transfer between Weyl points occurs between monopoles and antimonopoles due to chiral anomaly. This phenomenon is shown by the shift of the chemical potentials (arrows) in the figure, which drives the system into a nonequilibrium state. Anisotropy between WFs and anti-WFs (which is allowed by the broken inversion symmetry) leads to nonreciprocal current response in this nonequilibrium state induced by the chiral anomaly.