Symmetry-protected Spinful Magnetic Weyl Nodal Loops and Multi-Weyl Nodes in $5d^n$ Cubic Double Perovskites $(n=1,2)$

TL;DR

This paper investigates topological features in cubic ferromagnetic 5d^1,2 systems with strong spin-orbit coupling, revealing robust magnetic Weyl nodal loops and points, and highlighting a material with ideal half semimetal properties and high anomalous Hall conductivity.

Contribution

It introduces the discovery of symmetry-protected magnetic Weyl nodal loops and points in 5d cubic double perovskites, demonstrating their robustness and potential for large anomalous Hall effects.

Findings

Magnetic Weyl nodal loops are robust against SOC and correlation U variations.

Presence of magnetic Weyl points with chiral charges |χ|=1, 2 along symmetry lines.

Ba2ZnReO6 is an ideal half semimetal with high anomalous Hall conductivity.

Abstract

Using both an effective three-band model and {\it ab initio} calculations, we have investigated various topological features in the cubic ferromagnetic $5d^{1,2}$ systems showing large spin-orbit coupling (SOC): Ba$_2$NaOsO$_6$, Sr$_2$SrOsO$_6$, and Ba$_2$$B$ReO$_6$ ($B$= Mg, Zn). In the presence of time-reversal symmetry (${\cal T}$), spinless Dirac nodal loops linked to each other at the $W$ points appear in the mirror planes. Remarkably, breaking ${\cal T}$ leads to spinful magnetic Weyl nodal loops (MWNLs) that are robust even at large SOC and correlation strength $U$ variation due to the combination of mirror symmetry and broken ${\cal T}$. Additionally, there are two types of magnetic Weyl points with chiral charges $|\chi|=1, 2$ along the $C_{4v}$ symmetry line, and another type-II MWNL encircling the zone center, that are dependent on $U$. Furthermore, the ferromagnetic Ba$_2$ZnReO$_6$ is an ideal half semimetal with MWNLs and magnetic Weyl nodes at the Fermi level without the interference of topologically trivial bulk states. These systems give rise to a remarkably large anomalous Hall conductivity $\sigma_{xy}$ of up to 1160 ($\Omega$cm)$^{-1}$. Our findings may apply widely for $t_{2g}$ systems with cubic (or slightly distorted) fcc-like structures.