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 (Bi(1-x)Mn(x))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.

Department Chemie Ludwig Maximilians Universität München Butenandtstr 5 13 81377 München Germany

Department of Chemistry Moscow State University Leninskie Gory 1 3 119991 Moscow Russia

Department of Condensed Matter Physics CEITEC Masaryk University Kotlarska 2 61137 Brno Czech Republic

Department of Condensed Matter Physics Charles University Ke Karlovu 5 12116 Prague Czech Republic

Helmholtz Zentrum Berlin für Materialien und Energie Elektronenspeicherring BESSY 2 Albert Einstein Straße 15 12489 Berlin Germany

Institut für Halbleiter und Festkörperphysik Johannes Kepler Universität Altenbergerstr 69 4040 Linz Austria

New Technologies Research Centre University of West Bohemia Univerzitni 8 306 14 Pilsen Czech Republic

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