Eightfold Degenerate Dirac Nodal Line in Collinear Antiferromagnet Mn$_5$Si$_3$

TL;DR

This study reveals an eight-fold degenerate Dirac nodal line in Mn$_5$Si$_3$, protected by symmetry, which transforms under SOC, and predicts large spin Hall conductivity, highlighting its potential for spintronic applications.

Contribution

The paper uncovers an unconventional eight-fold degenerate Dirac nodal line in Mn$_5$Si$_3$ and analyzes its symmetry protection and effects of spin-orbit coupling, advancing understanding of topological features in antiferromagnets.

Findings

Identification of an eight-fold degenerate Dirac nodal line near the Fermi level.

Protection of the DNL by combined symmetry operations including magnetic space group symmetries.

Prediction of large intrinsic spin Hall conductivity related to the DNL features.

Abstract

We study the electronic, magnetic, and spin transport properties of the orthorhombic Mn$_{5}$Si$_{3}$ compound in the $AF2$ phase using symmetry analysis and ab-initio calculations. Our ground state energy calculations align with experimental observations, demonstrating that the collinear antiferromagnetic (AFM) order, with N\'{e}el vector in the [010] direction, is the most stable magnetic configuration both with and without spin-orbit coupling (SOC) in a bulk lattice geometry. We identified an unconventional eight-fold degenerate Dirac nodal line (DNL) close to the Fermi level, characterized by negligible SOC. This DNL is robustly protected by a unique combination of a pure-spin symmetry and a lattice symmetry together with magnetic space group symmetries. Upon introducing SOC, this degeneracy is reduced to two four-fold DNLs, being protected by the combination of time-reversal, partial translation and nonsymmorphic symmetries within the magnetic space group. We predict also a large intrinsic spin Hall conductivity (SHC) which correlates with the presence of SOC-induced splitting of these eight-fold degenerate DNLs near the Fermi level. These intriguing characteristics position collinear antiferromagnet Mn$_{5}$Si$_{3}$ as a compelling candidate for spintronic applications, particularly in the generation and detection of spin currents, while remaining compatible with modern silicon technology.