Exotic Spin-Orbital Physics in Hybrid Oxides

We compare the eective spin-orbital super- exchange triggered by magnetic 3d impurities with d3 and d2 congurations and either no orbital degree of freedom (orbital dilution) or hole replacing a doublon (charge dilution) in a 4d4 Mott insulator with S = 1 spins. Impurities causing orbital dilution act either as spin defects decoupled from the surrounding ions, or generate orbital polarons along d3-d4 hybrid bonds. The exchange on these bonds determines which orbital is oc- cupied by a doublon on the host site. In case of charge dilution by 3d2 impurities additional / T+ i T+ j terms arise which enhance orbital uctuations. We show that such terms may radically change orbital pattern at rela- tively low doping by x = 1=8 hole defects. Our ndings provide new perspective for future theoretical and ex- perimental studies of doped transition metal oxides.