Abstract
The atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is analyzed by surface x-ray absorption spectroscopy. Iron atoms deposited on a ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer. Iron atoms are neighbored by six selenium atoms at a distance in the 2.4 \AA{} range indicating substantial atomic relaxations. Mild annealing up to 520 K leads to the formation of $\ensuremath{\alpha}$-FeSe, characterized by a local order extending up to the sixth shell (5.80 \AA{}). Ab initio calculations predict a noncollinear magnetic ordering with a transition temperature of 3.5--10 K depending on the iron concentration and the number of the layers in which Fe is located.
Highlights
Topological Insulators (TIs) have been under focus in contemporary condensed matters physics research[1,2,3]
Iron atoms deposited on a Bi2Se3 (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer
From the experimental side there is an ongoing discussion regarding whether the doping of a TI surface with magnetic atoms leads to an opening of a gap at the Dirac point[16,18,26,27,28]
Summary
Topological Insulators (TIs) have been under focus in contemporary condensed matters physics research[1,2,3]. Semiconductors in the bulk, they host a gapless, linearly-dispersing state at the surface, which is a consequence of strong spin-orbit coupling The hallmark of this so-called topological surface state is a helical spin texture that protects surface electrons from backscattering on defects as long as time reversal symmetry is preserved[4,5]. Magnetic measurements found no evidence of the long-range FM order in the systems of Fe and Co adatoms at the Bi2Te329 and Bi2Se319,26,30 surfaces (the coverage in the latter case was reaching 0.9 monolayers) Interpretation of these magnetic and photoemission measurements requires detailed knowledge of the near-surface atomic structure, i.e. localization and distribution of the adsorbate. The experimentally obtained structural information is further utilized in a first principles study on magnetic properties of Fe/Bi2Se3(0001) within the density functional theory
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