Strain and onsite-correlation tunable quantum anomalous Hall phases in ferromagnetic (111) LaXO3 bilayers (X=Pd,Pt)

Quantum anomalous Hall (QAH) phases in magnetic topological insulators are characterized by the scattering-free chiral edge currents protected by their nontrivial bulk band topology. To fully explore these intriguing phenomena and application of topological insulators, high-temperature material realization of QAH phases is crucial. In this paper, based on extensive first-principles density functional theory calculations, we predict that perovskite bilayers ${({\mathrm{La}X\text{O}}_{3})}_{2}$ ($X$ = Pd, Pt) imbedded in the (111) ${({\mathrm{La}X\text{O}}_{3})}_{2}/{({\mathrm{LaAlO}}_{3})}_{10}$ superlattices are high-Curie-temperature ferromagnets that host both QAH and Dirac nodal ring semimetal phases, depending on the biaxial strain and onsite electron correlation. In particular, both the direction (the Chern number sign) and spin polarization of the chiral edge currents are tunable by either onsite electron correlation or biaxial in-plane strain. Furthermore, the nontrivial band gap can be enhanced up to 92 meV in the ${\mathrm{LaPdO}}_{3}$ bilayer by the compressive in-plane strain and can go up to as large as 242 meV when the Pd atoms are replaced by the heavier Pt atoms. Finally, the microscopic mechanisms of the ferromagnetic coupling and other interesting properties of the bilayers are uncovered by analyzing their underlying electronic band structures.