Abstract
Magnetic doping is expected to open a band gap at the Dirac point of topological insulators by breaking time-reversal symmetry and to enable novel topological phases. Epitaxial (Bi1−xMnx)2Se3 is a prototypical magnetic topological insulator with a pronounced surface band gap of ∼100 meV. We show that this gap is neither due to ferromagnetic order in the bulk or at the surface nor to the local magnetic moment of the Mn, making the system unsuitable for realizing the novel phases. We further show that Mn doping does not affect the inverted bulk band gap and the system remains topologically nontrivial. We suggest that strong resonant scattering processes cause the gap at the Dirac point and support this by the observation of in-gap states using resonant photoemission. Our findings establish a mechanism for gap opening in topological surface states which challenges the currently known conditions for topological protection.
Highlights
Magnetic doping is expected to open a band gap at the Dirac point of topological insulators by breaking time-reversal symmetry and to enable novel topological phases
Contributions from the bulk-conduction band (BCB) do not appear due to the dependence of the photoemission transitions on the component of the electron wave vector perpendicular to the surface k>, but the BCB is partially occupied as data at 21 eV photon energy reveal (Supplementary Fig. 1)
The pure Bi2Se3 film (Fig. 1a) is n-doped and exhibits a well-resolved Dirac point with high photoemission intensity at a binding energy of ED B0.4 eV that is seen as an intense peak in the energy-distribution curve at zero momentum superimposed as red curve on the right-hand side of the panel
Summary
Magnetic doping is expected to open a band gap at the Dirac point of topological insulators by breaking time-reversal symmetry and to enable novel topological phases. At the surface of a 3D TI, calculations show that magnetic impurities can open a gap at the Dirac point and exhibit ferromagnetic order with perpendicular anisotropy mediated by the TSS
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