Abstract
In 4d/5d transition-metal systems, many interesting physical properties arise from the interplay of bandwidth, electronic correlations, and spin-orbit interactions. Here, using ab initio density functional theory, we systematically study the double-perovskite-like system K2OsX6 (X=F,Cl,andBr) with a 5d4 electronic configuration. Our main result is that the J=0 nonmagnetic insulating state develops in this system, induced by strong spin-orbit coupling (SOC). Specifically, the well-separated OsX6 octahedra lead to the cubic crystal-field limit and result in dramatically decreasing hoppings among nearest neighbor Os-Os sites. In this case, the three degenerate t2g orbitals are reconstructed into two “effective” jeff (jeff=1/2 and jeff=3/2 states) states separated by the strong SOC, opening a gap with four electrons occupying the jeff=3/2 orbitals. Furthermore, the hybridization between the Os 5d orbitals and the X (X=F,Cl,andBr) p orbitals increases from F to Br, leading the electrons in K2OsF6 to be more localized than in K2OsCl6 and K2OsBr6, resulting in a smaller bandwidth for K2OsF6 than in the Cl- or Br-cases. Our results provide guidance to experimentalists and theorists working on this interesting family of osmium halides.
