Correlation effects in ruthenates: LDA+DMFT study

The ruthenates of the Ruddlesden-Popper family An+1Run O3n+1 where A=(Sr,Ca) are unique among transition-metal oxides, because the change of cation A and/or in the number n of RuO2 layers leads to a variety of collective phenomena, ranging from multi-band Mott transitions to ferro- and meta-magnetism. To understand these systems, it is necessary to disentangle the effects of Coulomb repulsion in the 4d4Ru shell from those of lattice distortions and chemistry. By using the LDA+DMFT approach, we show how such disentanglement explains the nature of the metal-insulator transition in single-layered Ca ruthenates and the evolution of electronic structure in n-layered Sr ruthenates. We use LDA+DMFT scheme based on the N-th Order Muffin-Tin Orbital approach and the weak-coupling CT-quantum Monte Carlo method as impurity solver. This method allows us to take into account the full rotationally-invariant Coulomb interaction, as well as full on-site self-energy matrix in orbital space with spin-orbit coupling. We discuss changes in effective mass and orbital polarization as a result of spin-flip processes and spin-orbit interaction.