Topological Gapless Phases in Non-Symmorphic Antiferromagnets

TL;DR

This paper uncovers new topological gapless phases in non-symmorphic antiferromagnets, revealing complex band crossings and topological protections that could lead to novel electronic states in magnetic materials.

Contribution

It demonstrates the existence of topological semimetal and metal phases with multiple band crossings in non-symmorphic antiferromagnets, introducing mechanisms for topological protection and phase transitions.

Findings

Identification of Dirac points with multiple symmetry protections

Discovery of triple and quadruple band-crossing points

Conversion of glide semimetals into topological phases with non-trivial  topological charges

Abstract

Topologically protected fermionic quasiparticles occur in metals with band degeneracy as a consequence of band structure topology. Here we unveil topological semimetal and metal phases in a variety of non-symmorphic collinear antiferromagnets with glide reflection symmetry, a combination of mirror and half-lattice translation. We find gapless phases with Dirac points having multiple symmetry-protection as well as electronic structures with triple and quadruple band-crossing points. Glide semimetal is shown to be converted into a topological phase with non-trivial $\mathbb{Z}_2$ topological charges at the Dirac points due to inversion and time-inversion symmetry combination. More striking is the emergence of a hidden non-unitary relation between the states in the glide sectors that provide a general mechanism to get multiple band touching points. The split Fermi points uncover a $\mathbb{Z}_2$ protection that drives the changeover of the multiple-degenerate gapless phase into a topological metal built from their connection through distinct Fermi lines. Besides a new perspective of ordered states in complex materials, our findings indicate that novel topological gapless phases and edge states may occur in a wide class of magnetic systems.