Two-dimensional Dirac nodal loop magnons in collinear antiferromagnets

TL;DR

This paper reveals the existence of symmetry-protected two-dimensional Dirac nodal loop magnons in collinear antiferromagnets on the CaVO lattice, offering a new platform for exploring topological magnonic phenomena.

Contribution

It demonstrates the presence of 2D Dirac nodal loop magnons in antiferromagnetic systems, a phenomenon absent in ferromagnets, due to specific symmetry protections.

Findings

DNLs are protected by $ ext{PT}$-symmetry in 2D antiferromagnets.

DNLs are absent in ferromagnetic counterparts.

The study links magnetic symmetry to topological magnon features.

Abstract

We study the nontrivial linear magnon band crossings in the collinear antiferromagnets on the two-dimensional (2D) CaVO lattice, also realized in some iron-based superconductors such as AFe$_{1.6+x}$Se$_2$ (A = K, Rb, Cs). It is shown that the combination of space-inversion and time-reversal symmetry ($\mathcal{PT}$-symmetry) leads to doubly-degenerate eight magnon branches, which cross each other linearly along a one-dimensional loop in the 2D Brillouin zone. We show that the Dirac nodal loops (DNLs) are not present in the collinear ferromagnet on this lattice. Thus, the current 2D antiferromagnetic DNLs are symmetry-protected and they provide a novel platform to search for their analogs in 2D electronic antiferromagnetic systems.