Large anomalous Hall, Nernst effect and topological phases in the 3d-4d/5d based oxide double perovskites

Magnetic topological quantum materials are attracting considerable attention owing to their potential technological applications. However, only a small number of these materials have been experimentally realized, thereby giving rise to the need for new stable magnetic topological quantum materials. Magnetism and spin-orbit coupling, two essential ingredients of the oxide materials, lead to various topological transport phenomena such as the anomalous Hall and anomalous Nernst effects, which can be significantly enhanced by designing an electronic structure with a large Berry curvature. In that respect, double perovskites with the general formula A$_2$BB'O$_6$ with an alternating ordered arrangement of two transition metal sites, B(3d) and B'(4d/5d), present attractive possibilities as they are robustly stable against oxidation under ambient conditions and versatile. These double perovskites also offer a high energy scale for magnetism as well as strong spin-orbit coupling with a high magnetic ordering temperature. Here, using first-principles density functional theory calculations, we present a comprehensive study of the intrinsic anomalous transport for 3d-4d/5d based cubic and tetragonal stable double perovskite (DP) compounds. A few of the DPs exhibit a very large anomalous Hall effect with a distinct topological band crossing in the vicinity of the Fermi energy. Our results show the importance of symmetries, particularly the mirror planes, as well as the clean topological band crossing near the Fermi energy, which is primarily contributed by the 5d-t$_{2g}$ for large anomalous Hall and Nernst effects.