Topological insulator Bi2Se3(111) surface doped with transition metals: An ab initio investigation

Based on first-principles calculations, we provide a map of the energetic stability and the electronic behavior of the topologically protected surface states of the topological insulator (TI), Bi2Se3, doped with transition metals (TMs), TM/Bi2Se3(111). We find that Fe, Mn, and Cr impurities are energetically more stable at the Bi substitutional sites, whereas we may find energetically stable substitutional as well as interstitial configurations for Co and Ni impurity atoms. Through scanning tunneling microscopy simulations, we verify that each TM atomic species and its position in the Bi2Se3(111) surface can be identified. The substitutional Fe and Cr impurities exhibit an energetic preference for the out-of-plane net magnetic moment, giving rise to a small energy gap at the Dirac point (DP), whereas the in-plane magnetic moment of substitutional Mn/Bi2Se3(111) promotes a shift of the DP from the center of the surface Brillouin zone, opening up a small energy gap. For the substitutional impurities, the shapes of the metallic bands are somewhat preserved compared with the energy bands of the pristine Bi2Se3(111) surface. Interstitial Co atoms also present an in-plane net magnetic moment, where we find the formation of metallic bands, suppressing the presence of the DP. For the Ni/Bi2Se3(111) impurity there is not a net magnetic moment, and therefore, the DP is preserved. Further formation energy results indicate other plausible (meta) stable impurity configurations, giving rise to quite different scenarios for the topological properties of TM/Bi2Se3(111), even for the same TM impurity.