Dirac fermions in an antiferromagnetic semimetal

The prediction of an antiferromagnetic semimetal that breaks both time-reversal and inversion symmetry but respects their combination could provide a platform for studying the interplay between Dirac fermions and magnetism. Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications 1 , 2 , 3 . Recently, massless Dirac fermions were found to emerge as low-energy excitations in materials now known as Dirac semimetals 4 , 5 , 6 . All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry and inversion symmetry 7 , 8 , 9 . Here we show that Dirac fermions can exist in one type of antiferromagnetic system, where both and are broken but their combination 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.