Cubic Double Perovskites*

5d systems show abundant physical phenomena due to an interplay between strong spin-orbit coupling (SOC) and moderate correlation, vz. the Dirac-Mott metal-insulator transitions in Os-based oxides. In topological characters, various symmetries, SOC, and (sometimes) strength of correlation are key ingredients to generate topologically nontrivial phases.
Using the ab initioapproach, we have investigated topological characters in the Os-based cubic double perovskites of 5d¹and 5d²which have a strong SOC, moderate correlation, and plentiful crystal symmetries. In our GGA results of both nonmagnetic(NM) and ferromagnetic(FM) cases, there are nodal lines around W and K points. Even for considering SOC, in the TRS-broken cases the nodal lines are robust on k_z=0 plane, which is perpendicular to the direction of [001] SOC, whereas these disappear in the NM cases. Besides, in the TRS-broken cases, 14 pairs of Weyl points with opposite chirality on the mirror planes appear. Applying correlation as well as SOC, the nodal lines remain protected, while the WPs vanish. In this presentation, we will analyze the mechanisms of topological characters in the Os-based cubic double perovskites.