Gap-like feature observed in the non-magnetic topological insulators

Abstract

Non-magnetic gap at the Dirac point of topological insulators remains an open question in the field. Here, we present angle-resolved photoemission spectroscopy experiments performed on Cr-doped Bi 2 Se 3 and showed that the Dirac point is progressively buried by the bulk bands and a low spectral weight region in the vicinity of the Dirac point appears. These two mechanisms lead to spectral weight suppression region being mistakenly identified as an energy gap in earlier studies. We further calculated the band structure and found that the original Dirac point splits into two nodes due to the impurity resonant states and the energy separation between the nodes is the low density of state region which appears to be like an energy gap in potoemission experiments. We supported our arguments by presenting photoemission experiments carried out with on-and off-resonant photon energies. Our observation resolves the widely debated questions of apparent energy gap opening at the Dirac point without long range ferromagnetic order in topological insulators.

Dirac node engineering and flat bands in doped Dirac materials

“…Moreover, recent ARPES studies suggested that overlapping of impurity resonances with the Dirac node, a situation depicted in Fig. 1(b), could be achieved in the experiment as the binding energy of the node changes with increasing the film thickness 25 . It is also possible to resolve, at least partially, the impurity bands by adjusting the photon energy of the pulse.…”

“…Recent experiments indicate that favourable conditions can be achieved at least for some samples and dopants, e.g. for Cr in Bi 2 Se 3 above the magnetic ordering temperature 25 .…”