Third-order charge transport in a magnetic topological semimetal

Magnetic topological materials and their physical signatures are a focus of current research. By first-principles calculations and symmetry analysis, we reveal exotic topological semimetal states in an existing antiferromagnet ThMn2Si2. Depending on the Neel vector orientation, the topological band crossings near the Fermi level form either a double-nodal loop or two pairs of Dirac points, which are all fourfold degenerate and robust under spin-orbit coupling. These topological features produce large Berry connection polarizability, leading to pronounced nonlinear transport effects. Particularly, we evaluate the third-order current response, which dominates the transverse current in ThMn2Si2. We show that the third-order response can be much more sensitive to topological phase transitions than a linear response, which offers a powerful tool for characterizing topological states of matter.