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 (Bi(1-x)Mn(x))2Se3 is a prototypical magnetic topological insulator with a pronounced surface band gap of â¼100 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.
ABSTRACT
Ferromagnetic Ge(1-x)Mn(x)Te is a promising candidate for diluted magnetic semiconductors because solid solutions exist over a wide range of compositions up to x(Mn)≈0.5, where a maximum in the total magnetization occurs. In this work, a systematic study of molecular beam epitaxy of GeMnTe on (1 1 1) BaF(2) substrates is presented, in which the Mn concentration as well as growth conditions were varied over a wide range. The results demonstrate that single phase growth of GeMnTe can be achieved only in a narrow window of growth conditions, whereas at low as well as high temperatures secondary phases or even phase separation occurs. The formation of secondary phases strongly reduces the layer magnetization as well as the Curie temperatures. Under optimized conditions, single phase GeMnTe layers are obtained with Curie temperatures as high as 200 K for Mn concentrations close to the solubility limit of x(Mn)=50%.
