Dirac fermions in the antiferromagnetic spintronics material CuMnAs

Dirac semimetals (DSMs) are the focus of study as new candidates for topological superconductivity and spintronics. Although the Dirac points are not necessarily associated with crystalline symmetries, the experimentally realized robust DSMs such as $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ have fourfold-degenerate Dirac points at generic wave vectors on high symmetry line enabled by a fourfold crystalline symmetry. The magnetic counterpart of these robust DSMs remains unknown. On the other hand, the theoretically proposed magnetic DSMs in potential antiferromagnetic (AFM) spintronics materials where both time-reversal $(\mathcal{T})$ and inversion $(\mathcal{P})$ symmetry are broken but their combination $\mathcal{P}\mathcal{T}$ is preserved have Dirac points on the boundary of the Brillouin zone protected by a low-order twofold crystalline symmetry. Here, combined with first-principles calculations and symmetry analysis, we find the Dirac fermion at generic wave vector on high symmetry line with associated nontrivial surface states in $\mathcal{P}\mathcal{T}$-symmetric tetragonal CuMnAs, which is the prototype AFM spintronics material observed in experiments. Furthermore, we reveal the hidden spin textures in this $\mathcal{P}\mathcal{T}$-symmetric magnetic system, demonstrating interesting vortex-like spin textures. Our study opens the way for designing robust magnetic DSMs that can serve as an ideal platform to study the interplay of magnetism, Dirac fermions, and spin-orbit interactions, and could stimulate a series of research in the field of topological antiferromagnetic spintronics.