Topological Insulator and Magnetic Insulator Heterostructures for Quantum Anomalous Hall Effect (QAHE) Applications

Topological insulators (TIs) provide a unique platform for realizing the quantum anomalous Hall effect (QAHE), where dissipationless edge transport emerges without external magnetic fields. However, the effect has so far required millikelvin temperatures, which limited the electrical metrology applications. Engineering proximity coupling between TIs and magnetic insulators (MIs) offers a promising route to enhance magnetic exchange and raise QAHE operating temperatures into few-kelvin regime. Here, we report advances in the epitaxial growth and optimization of single-phase Bi₂Te₃, (Bi,Sb)₂Te₃ (BST), and V-doped BST films with smooth surfaces, confirmed by HRXRD, RHEED, AFM, and Raman spectroscopy. Our density functional theory calculations helped identify the surface and bulk phonon mode signatures in the experimental Raman spectra. Tm₃Fe₅O₁₂ with out-of-plane magnetic anisotropy and Ho₃Fe₅O₁₂ films with easy plane were grown using pulsed laser deposition. The films have strain-tunable magnetic anisotropy and robust interfacial exchange verified by polarized neutron reflectometry. Hall bar devices fabricated from these heterostructures are under low-temperature testing to achieve quantized resistance plateaus, which might represent an important step toward redefining electrical resistance standards and advancing spintronic device applications.