Magnetically-driven orbital-selective insulator-to-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-to-metal transition in rock-salt ordered double perovskite oxides A₂BB′O₆ where B is a nonmagnetic ion and B′ a magnetic ion with a d³ electronic configuration (Tc⁴⁺, Ru⁵⁺, Os⁵⁺ etc.). The orbital selectivity originates from geometry 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. Our work shows that by exploiting geometry 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.