Magnetically-driven orbital-selective insulator-metal transition in double perovskite oxides

Interaction-driven metal-insulator transitions or Mott transitions are widely observed in condensed-matter systems. In multi-orbital systems, many-body physics is richer in which an orbital-selective metal-insulator transition is an intriguing and unique phenomenon. Here we use first-principles calculations to show that a magnetic transition (from paramagnetic to long-range magnetically ordered) can simultaneously induce an orbital-selective insulator-metal transition in rock-salt ordered double perovskite oxides $A_2BB'$O$_6$ where $B$ is a non-magnetic ion (Y$^{3+}$ and Sc$^{3+}$) and $B'$ a magnetic ion with a $d^3$ electronic configuration (Ru$^{5+}$ and Os$^{5+}$). The orbital selectivity originates from geometrical frustration of a face-centered-cubic lattice on which the magnetic ions $B'$ reside. Including realistic structural distortions and spin-orbit interaction do not affect the transition. The predicted orbital-selective transition naturally explains the anomaly observed in the electric resistivity of Sr$_2$YRuO$_6$. Implications of other available experimental data are also discussed. Our work shows that by exploiting geometrical frustration on non-bipartite lattices, novel electronic/magnetic/orbital-coupled phase transitions can occur in correlated materials that are in the vicinity of metal-insulator phase boundary.