Fabricating a hexagonal FeTe monolayer with a moiré superlattice on topological insulator Bi₂Te₃

The growth of a hexagonal FeTe (α-FeTe) thin layer on three-dimensional topological insulator Bi₂Te₃ has been systematically investigated by combining scanning tunneling microscopy/spectroscopy (STM/STS) with density-functional theory (DFT) calculations. Through post-annealing at 560 K after room-temperature deposition of Fe onto Bi₂Te₃, α-FeTe has been fabricated with an atomic lattice constant of 4.0 ± 0.1 Å, which is much smaller than the 4.4 ± 0.1 Å of the Te-terminated Bi₂Te₃ surface. The lattice mismatch and a sufficiently large FeTe-Bi₂Te₃ distance give rise to a moiré pattern with a periodicity of 6.0 ± 0.1 nm, corresponding to a p(15 × 15) superlattice. On the other hand, an enhanced projected density of states (PDOS) is found at about -0.8 eV and +1.4 eV of α-FeTe/Bi₂Te₃ in the tunneling spectra. These enhancements, as interpreted from the DFT calculation, arise from the contribution of the 3d out-of-plane orbitals in Fe. DFT calculations also reveal nonzero net magnetization and indicate ferromagnetic (FM) order in the system - contrasting the well-studied bicollinear antiferromagnetism in β-FeTe/Bi₂Te₃. To summarize, our successful fabrication of α-FeTe/Bi₂Te₃ provides a distinct platform from β-FeTe/Bi₂Te₃, enabling an exploration of the interplay between magnetism and interface-induced superconductivity.