Spin-polarized scanning tunneling microscopy of Fe adatoms on Bi₂Te₃

Introducing magnetic defects to the surface states of topological insulators, such as Bi₂(Te, Se)₃, can lead to intriguing phenomena including the opening of a magnetic gap, induced complex spin textures, and the quantum anomalous Hall effect. Using spin-polarized scanning tunneling microscopy (SPSTM) and density-functional theory (DFT) based first-principles calculations, we investigate the adsorption behavior and electronic structure of fcc-Fe adatoms on the Te-terminated surface of Bi₂Te₃. Fe adatoms were deposited and studied at 5K and room temperature. At room temperature, Fe adatoms were easily perturbed by the STM tip during scanning, leading to the formation of small 3D clusters or planar, 2D islands. STM imaging of the 2D islands reveals stochastic changes in contrast that we attribute to magnetization switching dynamics. At low-temperature deposition, topographic imaging reveals Fe adatoms occupying fcc and hcp hollow sites. Topographic imaging of fcc-Fe shows a distinct 3-fold symmetry, in good agreement with the DFT results. In contrast, differential conductance (dI/dV) imaging and spectroscopy reveal lower-dimensional symmetry in the partial local density of states, not observed in prior reports. These results may be attributed to a symmetry-dependent overlap of the Fe 3d orbitals and the neighboring Te atoms. Our approach combining SPSTM and DFT, aims toward providing insights into the coupling mechanisms between magnetic defects and topological surface states.