"Special Seminar: Spin-orbital frustration in Mott insulators"

 

 

 

In Mott insulators, unquenched orbital degrees of freedom often frustrate the magnetic interactions and lead to a plethora of interesting phases with unusual spin patterns or non-magnetic states without long-range order. I will review from this perspective the theoretical concepts and experimental data on late transition metal compounds, mostly focusing on iridates. In the second part, I will present our recent theoretical study of interplay of spin and orbital degrees in double-perovskite compounds with spin one-half ions occupying the fcc sub-sublattice, such as molybdenum and osmium oxides. I will argue that this interplay might lead to a rich variety of the phases that include non-collinear ordered patterns with or without net moment, and, most remarkably, non-magnetic disordered spin-orbit dimer state.