  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
(LaXO$_3$)$_{2}$ (X = Pd, Pt) imbedded in the (111)
(LaXO$_3$)$_{2}$/(LaAlO$_3$)$_{10}$ superlattices are high Curie temperature
ferromagnets that host both QAH and Dirac semimetal phases, depending on the
biaxial strain and onsite electron correlation. In particular, both the
direction (the sign of Chern number) 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 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.
