Native point defects and their implications for the Dirac point gap at MnBi₂Te₄(0001)

The Dirac point gap at the surface of the antiferromagnetic topological insulator MnBi₂Te₄ (MBT) is a highly debated issue [1-3]. While the early photoemission measurements reported on large gaps in agreement with theoretical predictions, other experiments found vanishingly small splitting of the MBT Dirac cone. Here, we study the effect of the native point defects on the MBT surface electronic structure using the density functional theory calculations [4]. The results of our scanning tunneling microscopy images simulations are consistent with the presence of the Bi_Te antisites (Bi atoms at the Te sites) and Mn_Bi substitutions (Mn atoms at the Bi sites). Our surface electronic structure calculations show that, due to the predominant localization of the topological surface state near the Bi layers, Mn_Bi defects can cause a strong reduction of the MBT Dirac point gap [4], given the recently proved [5] antiparallel alignment of the Mn_Bi moments with respect to those of the Mn layer. Our results provide important insights into the MBT Dirac point gap mystery.

1 M Otrokov et al, Nature 576, 412 (2019)

2 Y Hao et al, Phys. Rev. X 9, 041038 (2019)

3 A Shikin et al, Phys. Rev. B 104, 115168 (2021)

4 M Garnica, M. Otrokov et al, arXiv:2109.01615

5 Y Lai et al, Phys. Rev. B 103, 184429 (2021)