Applying the correlated electronic structure method based on density functional theory plus Hubbard U interaction, we have investigated the tetragonal scheelite structure Mott insulator KOsO4, whose e 1 g configuration should be affected little by spin-orbit couping (SOC). The method reproduces the observed antiferromagnetic Mott insulating state, populating the Os d z 2 majority orbital. The quarter-filled eg manifold is characterized by a symmetry breaking due to the tetragonal structure, and the Os ion shows a crystal field splitting ∆ cf = 1.7 eV from the t2g complex, relatively small considering the high formal oxidation state Os 7+ . The small magnetocrystalline anisotropy before including correlation (i.e. in the metallic state) is increased by more than an order of magnitude in the Mott insulating state, a result of strong interplay between large SOC and strong correlation. In contrast to conventional wisdom that the eg complex will not support orbital magnetism, we find that for the easy axis [100] direction the substantial Os orbital moment ML ≈ −0.2µB that compensates half of the Os spin moment MS=0.4 µB. The origin of the orbital moment is analyzed and understood in terms of additional spin-orbital lowering of symmetry, beyond that due to structural distortion, for magnetization along [100]. Further interpretation is assisted by analysis of the spin density and the Wannier function with SOC included.

The nearly well-ordered double perovskite La2CrFeO6 has been synthesized recently. Contrary to previous theoretical predictions, but in agreement with experimental observations, our first principle calculations indicate an insulating ferrimagnet La2CrFeO6 with antialigned S= Fe 3+ ions, using the local spin density approximation (LSDA), a correlated band theory LDA+U, and a semilocal functional modified Becke-Johnson method. Additionally, we investigated the double perovskite Sr2CrFeO6, which is as yet unsynthesized. In LSDA calculations, this system shows formally tetravalent Cr and Fe ions both having antialigned S=1 moments, but is a simple metal. Once applying on-site Coulomb repulsion U on both Cr and Fe ions, this system becomes halfmetallic and the moment of Fe is substantially reduced, resulting in zero net moment. These results are consistent with our fixed spin moment studies. Our results suggest a precisely compensated half-metallic Sr2CrFeO6.

There is strong interest in discovering or designing wide gap Chern insulators. Here we follow a Chern insulator to trivial Mott insulator transition versus interaction strength U in a honeycomb lattice Fe-based transition metal oxide, discovering that a spin-orbit coupling energy scale ξ=40 meV can produce and maintain a topologically entangled Chern insulating state against large band structure changes arising from an interaction strength U up to 60 times as large. Within the Chern phase the minimum gap switches from the zone corner K to the zone center Γ while maintaining the topological structure. At a critical strength Uc, the continuous evolution of the electronic structure encounters a gap closing then reopening, upon which the system reverts to a trivial Mott insulating phase. This Chern insulator phase of honeycomb lattice Fe 2+ BaFe2(PO4)2 corresponds to a large Chern number C = -3 that will provide enhanced anomalous Hall conductivity due to the associated three edge states threading through the bulk gap of 80 meV.

We investigate the electronic structure and several properties, and topological character, of the cubic time-reversal invariant intermetallic compounds PbPd3 and SnPd3 using density functional theory based methods. These compounds have a dispersionless band along the Γ − X line, forming the top of the Pd 4d bands and lying within a few meV of the Fermi level EF . Effects of the flat band on transport and optical properties have been inspected by varying the doping concentration treated with the virtual crystal approximation for substitution on the Pb site. In the absence of spin-orbit coupling (SOC), we find triple nodal points and three-dimensional nodal loops, which are known to lead to surface bands and drumhead states, respectively, which we discuss for PbPd3. SOC removes degeneracy in most of the zone, providing a topological index Z2=1 on the kz = 0 plane that indicates a topological character on that plane. The isovalent and isostructural compound SnPd3 shows only minor differences in its electronic structures, so it is expected to display similar electronic, transport, and topological properties.PACS numbers: