A topological Hund nodal line antiferromagnet

TL;DR

This paper reports the discovery of a magnetic Dirac nodal line in YMn2Ge2, where topology, magnetism, and correlations interplay, revealing a Hund coupling effect on the electronic structure.

Contribution

It introduces the concept of an antiferromagnetic Hund nodal line, demonstrating how electronic correlations influence magnetic topological nodal lines.

Findings

Visualization of a fourfold degenerate Dirac nodal line.

The nodal line is enforced by symmetry and magnetism.

Observation of Hund coupling effects on the nodal line.

Abstract

The interplay of topology, magnetism, and correlations gives rise to intriguing phases of matter. In this study, through state-of-the-art angle-resolved photoemission spectroscopy, density functional theory and dynamical mean-field theory calculations, we visualize a fourfold degenerate Dirac nodal line at the boundary of the bulk Brillouin zone in the antiferromagnet YMn2Ge2. We further demonstrate that this gapless, antiferromagnetic Dirac nodal line is enforced by the combination of magnetism, space-time inversion symmetry and nonsymmorphic lattice symmetry. The corresponding drumhead surface states traverse the whole surface Brillouin zone. YMn2Ge2 thus serves as a platform to exhibit the interplay of multiple degenerate nodal physics and antiferromagnetism. Interestingly, the magnetic nodal line displays a d-orbital dependent renormalization along its trajectory in momentum space, thereby manifesting Hund coupling. Our findings offer insights into the effect of electronic correlations on magnetic Dirac nodal lines, leading to an antiferromagnetic Hund nodal line.