Fe dopants and surface adatoms versus nontrivial topology of single-crystalline Bi2Se3

Abstract

Both preserved gapless states and gapping of Dirac states due to broken time reversal symmetry in bismuth chalcogenide topological insulators with surface and bulk magnetic impurities have been observed and reported in the literature. In order to shed more light on the mechanism of such effects we have performed comprehensive element selective study of the impact of Fe impurity position in the Bi _2 Se _3 lattice on its magnetism. The iron atoms were imbedded in the structure (volume dopants) or deposited on the surface (adatoms) and they revealed striking phenomena. Volume doping preserves non-trivial topology of Bi _1.98 Fe _0.02 Se _3 . Fe atoms not only substitute Bi, but also locate in van der Waals gap. The former are magnetically isotropic, while the latter reveal large magnetic moment (4.5 μ _B ) with perpendicular anisotropy if located near the surface. Majority of Fe adatoms on the surface of Bi _2 Se _3 exhibit weaker moment (3.5 μ _B ) with in-plane anisotropy, as expected for non-interacting species. Negligible interaction between surface electronic states and magnetic adatoms is confirmed by identical vibration spectra of Fe deposited on TI surface of Bi _2 Se _3 and non-TI surface of Bi _2 S _3 . The data gathered show how indispensable is the knowledge of the magnetic impurity distribution for applications of bismuth chalcogenide systems.

Keywords

• topological insulator
• surface state
• quantum oscillations
• adatoms vibrations