High-temperature large-gap quantum anomalous Hall insulating state in ultrathin double perovskite films

Towards the goal of realizing topological phases in thin films of correlated oxide and heterostructures, we propose here a quantum anomalous Hall insulator (QAHI) in ultrathin films of double perovskites based on mixed 3d-5d or 3d-4d transition-metal ions, grown along the [111] direction. Considering the specific case of ultrathin Ba₂FeReO₆, we present a theoretical analysis of an effective Hamiltonian derived from first principles. We establish that a strong spin-orbit coupling at the Re site, t2g symmetry of the low-energy d bands, polarity of its [111] orientation of perovskite structure, and mixed 3d-5d chemistry results in room temperature magnetism with a robust QAHI state of Chern number $C=1$ and a large band gap. We uncover and highlight a nonrelativistic orbital Rashba-type effect in addition to the spin-orbit coupling, that governs this QAHI state. With a band gap of ~100 meV in electronic structure and magnetic transition temperature Tc~3000.28em0exK estimated by Monte Carlo simulations, our finding of the QAHI state in ultrathin Ba₂FeReO₆ is expected to stimulate experimental verification along with possible practical applications of its dissipationless edge currents.