Dirac fermions in an antiferromagnetic semimetal

Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications(1-3). Recently, massless Dirac fermionswere found to emerge as low-energy excitations in materials now known as Dirac semimetals(4-6). All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry T and inversion symmetry P7-9. Here we show that Dirac fermions can exist in one type of antiferromagnetic system, where both T and P are broken but their combination P T is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyse the robustness of the Dirac points under symmetry protections and demonstrate its distinctive bulk dispersions, as well as the corresponding surface states, by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism.