Spectral weight suppression as a gap-like feature in the non-magnetic states of topological insulators

Here, we present an answer to one of the much debated questions in the topological insulator research, i.e., the opening of an energy gap-like feature at the Dirac point without long range ferromagnetic order. This is in sharp contrast to the topological protection of the surface states against non-magnetic perturbations. We carried out a systematic photoemission study on Cr-doped Bi₂Se₃ films grown on pristine Bi₂Se₃ films which allow us to monitor the evolution of the topological electronic structure. Our angle-resolved photoemission spectroscopy experiments revealed a gap-like feature appears just below the Dirac point leaving the Dirac point unaffected by the doping. Furthermore, the Dirac point is buried under the bulk conduction band which prevented it from being resolved in previous photoemission experiments. The spectral weight suppression just below the Dirac point leads to the gap-like feature being mistakenly identified as an energy gap at the Dirac point.