A topological Hund nodal line antiferromagnet

The interaction of topology, magnetism, and correlations leads to fascinating phases of matter. In this research, we use angle-resolved photoemission spectroscopy, density functional theory, and dynamical mean-field theory calculations to reveal a fourfold degenerate Dirac nodal line at the boundary of the bulk Brillouin zone in the antiferromagnet YMn2Ge2. We show that this gapless, antiferromagnetic Dirac nodal line arises from the combination of magnetism, space-time inversion symmetry, and nonsymmorphic lattice symmetry. The related drumhead surface states span the entire surface Brillouin zone. Thus, YMn2Ge2 serves as a platform to explore the interplay of multiple degenerate nodal physics and antiferromagnetism. Notably, the magnetic nodal line exhibits a d-orbital dependent renormalization, highlighting the influence of Hund's coupling. Our results provide insights into how electronic correlations affect magnetic Dirac nodal lines, resulting in an antiferromagnetic Hund nodal line.