Chiral anomaly and internode scatterings in multifold semimetals

Abstract

In our quest to unravel the topological properties of nodal points in three-dimensional semimetals, one hallmark property which warrants our attention is the \textit{chiral anomaly}. In the Brillouin zone (BZ), the sign of the Berry-curvature field's monopole charge is referred to as the chirality ($\chi$) of the node, leading to the notion of chiral quasiparticles sourcing chiral currents, induced by internode scatterings proportional to the chiral anomaly. Here, we derive the generic form of the chiral conductivity when we have multifold nodes. Since the sum of all the monopole charges in the BZ is constrained to vanish, the nodes appear in pairs of $\chi =\pm 1$. Hence, the presence of band-crossing degeneracies of order higher than two make it possible to have two distinct scenarios: the pair of conjugate nodes in question comprise bands of (1) the same pseudospin variety and exhibiting Berry-curvature profiles differing by an overall factor of $\chi$, or (2) two distinct pseudospin representations. Covering these two possibilities, we apply our derived formula to semimetals harbouring triple-point (threefold-degenerate) and Rarita-Schwinger-Weyl (fourfold-degenerate) nodes, and show the resulting expressions for the conductivity featuring the chiral anomaly.