Two-component anomalous Hall effect in a magnetically doped topological insulator

We report on observation of the anomalous Hall (AH) effect that has been elusive in Mn-doped Bi₂Se₃ thin films. As the Mn concentration is increased, the sign of AH resistances can be changed from positive to negative, and these two types of AH resistances are found to coexist in the crossover regime. Such a two-component AH effect and the sign reversal can also be obtained by lowering the chemical potential in the samples with low Mn-doping levels. Based on their different dependences on the gate voltage and magnetic field, the positive and negative AH components are assigned to the bulk and surface states, respectively. Our results provide a missing experimental piece for understanding the puzzling interplay between the surface states and the magnetic doping effects in this prototype three-dimensional topological insulator (TI). The knowledge gained in this work will be valuable for optimizing magnetically doped TIs and hybrid structures, which have become a promising platform for observing novel quantum phenomena and realizing spintronic applications.