Quantum anomalous Hall phase and half-metallic phase in ferromagnetic (111) bilayers of 4d and 5d transition metal perovskites

Extraordinary electronic phases can form in artificial oxide heterostructures, which will provide a fertile ground for new physics and also give rise to novel device functions. Based on a systematic first-principles density functional theory study of the magnetic and electronic properties of the (111) superlattices ${({AB\text{O}}₃)}₂/{({AB}^{\ensuremath{'}}{\mathrm{O}}₃)}₁₀$ of $4d$ and $5d$ transition metal perovskite ($B$ = Ru, Rh, Ag, Re, Os, Ir, Au; ${AB}^{\ensuremath{'}}{\mathrm{O}}₃={\mathrm{LaAlO}}₃, {\mathrm{SrTiO}}₃)$, we demonstrate that due to quantum confinement, bilayers ${({\text{La}B\text{O}}₃)}₂$ ($B$ = Ru, Re, Os) and ${({\text{Sr}B\text{O}}₃)}₂$ ($B$ = Rh, Os, Ir) are ferromagnetic with ordering temperatures up to room temperature. In particular, bilayer ${({\mathrm{LaOsO}}₃)}₂$ is an exotic spin-polarized quantum anomalous Hall insulator, while the other ferromagnetic bilayers are metallic with large Hall conductances comparable to the conductance quantum. Furthermore, bilayers ${({\mathrm{LaRuO}}₃)}₂$ and ${({\mathrm{SrRhO}}₃)}₂$ are half metallic, while the bilayer ${({\mathrm{SrIrO}}₃)}₂$ exhibits a peculiar colossal magnetic anisotropy. Our findings thus show that $4d$ and $5d$ metal perovskite (111) bilayers are a class of quasi-two-dimensional materials for exploring exotic quantum phases and also for advanced applications such as low-power nanoelectronics and oxide spintronics.