First-Principles Study of Robust Magnetic Weyl Nodal Loops in 5d Cubic Double Perovskites*

Topological phenomena have been extensively studied due to their interesting properties in the condensed matter physics. In particular, topological nodal line phases have special features of dispersionless surface states, so-called drumhead surface states. These flat states lead to a large surface density of states, implying instabilities toward surface magnetism or superconductivity.
In this presentation, we will address a few Os-based cubic double perovskites possessing robust magnetic Weyl nodal lines (WNLs), protected by the mirror symmetry, even for considering spin-orbital coupling (SOC). Using first-principles and tight-binding approaches, we have investigated the nature of topological properties in the osmates. Our effective 3-band model of the isolated t_2g orbitals indicates that the ddσ and ddπ hoppings result in the nodal lines on the mirror planes. When including both correlation and SOC, these nodal lines are robust only in the broken time-reversal symmetry (TRS) case. Besides, remarkably, our calculated anomalous Hall conductivity shows a single sharp peak at the energy of WNLs due to a strong magnetic anisotropy, implying these WNLs to be experimentally observable.