Irremovable Mn-Bi Site Mixing in MnBi2Te4

MnBi2Te4, an antiferromagnetictopologicalinsulator, was theoretically predicted to have a gapped surface stateon its (111) surface. However, a much smaller gapped or even gaplesssurface state has been observed experimentally, which is thought tobe caused by the defects in MnBi2Te4. Here,we have theoretically identified the antisite Mn-Bi andBi(Mn) as dominant defects and revealed their evolution duringthe phase transition from MnTe/Bi2Te3 to MnBi2Te4. We found that the complete elimination ofMn(Bi) and Bi-Mn defects in MnBi2Te4 by simple annealing is almost impossible due to the highmigration barrier in kinetics. Moreover, the gap of the Dirac point-relatedbands in a MnBi2Te4 monolayer would be eliminatedwith an increasing concentration of Mn-Bi and Bi-Mn defects, which could explain the experimentally unobserved large-gapsurface state in MnBi2Te4. Our results providean insight into the theoretical understanding of the quality and theexperimentally measured topological properties of the synthesizedMnBi(2)Te(4).

Automated summary

The theoretically predicted gapped surface state of antiferromagnetic topological insulator MnBi2Te4 has been experimentally observed to have a smaller or even gapless surface state, which is caused by the defects in MnBi2Te4. The study identifies antisite Mn-Bi and Bi(Mn) as dominant defects and reveals their evolution during the phase transition from MnTe/Bi2Te3 to MnBi2Te4. It is found that complete elimination of Mn(Bi) and Bi-Mn defects in MnBi2Te4 through simple annealing is almost impossible due to high migration barrier in kinetics. Moreover, increasing concentration of Mn-Bi and Bi-Mn defects in MnBi2Te4 monolayer leads to the elimination of gap in the Dirac point-related bands, explaining the experimentally unobserved large-gap surface state. The results provide insight into the theoretical understanding of the synthesized MnBi2Te4's quality and experimentally measured topological properties.