Type-I and type-II Nodal Lines Coexistence in the Antiferromagnetic monolayer CrAs$_{2}$

TL;DR

This paper reports the discovery of coexisting type-I and type-II topological nodal lines in antiferromagnetic monolayer CrAs$_{2}$, revealing new topological phases protected by symmetries in magnetic systems.

Contribution

It demonstrates the coexistence of type-I and type-II nodal lines in a magnetic monolayer, protected by nonsymmorphic and mirror symmetries, based on first-principles calculations.

Findings

Type-I nodal line forms a concentric loop around the $B3$ point.

Type-II nodal lines are open and appear around the Fermi level.

Nodal lines are protected by symmetries and robust against spin-orbital coupling.

Abstract

Topological nodal line semimetals, hosting one-dimensional Fermi lines with symmetry protection, has become a hot topic in topological quantum matter. Due to the breaking of time reversal symmetry in magnetic system, nodal lines require protection by additional symmetries. Here, we report the discovery of antiferromagnetic type-I and type-II nodal lines coexist in the monolayer CrAs$_{2}$ based on a systematic first-principles calculation. Remarkably, the type-I nodal line in CrAs$_{2}$ form a concentric loop centered around the $\Gamma$ point is filling-enforced by nonsymmorphic analogue symmetry and robust against spin-orbital coupling. The type-II nodal lines, a kind of open nodal lines appear around the Fermi level, are protected by the mirror symmetry in the absence of spin-orbital coupling. The antiferromagnetic monolayer CrAs$_{2}$ proposed here may provide a platform for the correlation between magnetism and exotic topological phases.