Cartesian Nodal Lines and Magnetic Kramers Weyl Nodes in Spin-Split Antiferromagnets

TL;DR

This paper explores how spin-split antiferromagnets can host unique topological band degeneracies, such as Cartesian nodal lines and magnetic Kramers Weyl nodes, leading to novel boundary states and quantized effects.

Contribution

It identifies and characterizes two new types of symmetry-protected band degeneracies in spin-split antiferromagnets, expanding the understanding of their topological properties.

Findings

Presence of Cartesian nodal lines without spin-orbit coupling

Existence of magnetic Kramers Weyl nodes with spin-orbit coupling

Potential for quantized anomalous Hall and circular photogalvanic effects

Abstract

When band degeneracy occurs in a spin-split band structure, it gives rise to divergent Berry curvature and distinctive topological boundary states, resulting in a variety of fascinating effects. We show that three-dimensional spin-split antiferromagnets, characterized by symmetry-constrained momentum-dependent spin splitting and zero net magnetization, can host two unique forms of symmetry-protected band degeneracy: Cartesian nodal lines in the absence of spin-orbit coupling, and magnetic Kramers Weyl nodes when spin-orbit coupling is present. Remarkably, these band degeneracies not only produce unique patterns of Berry-curvature distributions but also give rise to topological boundary states with unconventional spin textures. Furthermore, we find that these band degeneracies can lead to strong or even quantized anomalous Hall effects and quantized circular photogalvanic effects under appropriate conditions. Our study suggests that spin-split antiferromagnets provide a fertile ground for exploring unconventional topological phases.