Intrinsic Magnetic Topological Insulators of the MnBi₂Te₄ Family: Current Status

Recently, MnBi₂Te₄ has been theoretically predicted and then experimentally confirmed to be the first intrinsic antiferromagnetic TI (AFMTI) [1-3]. This opens a new field that focuses on intrinsically magnetic stoichiometric compounds: several MnBi₂Te₄-derived MTIs were synthesized right away [4], such as (MnBi₂Te₄)·n(Bi₂Te₃), MnBi_2−xSb_xTe₄, (MnSb₂Te₄)·n(Sb₂Te₃), Mn₂(Bi,Sb)₂Te₅, and MnBi₂Se₄, that will also be discussed in the talk. As a result, MnBi₂Te₄ has been predicted to be a platform for realizing high-order topological insulator and superconductor states, Weyl semimetal phase, skyrmions, quantized magnetoeletric coupling, and Majorana fermions. Moreover, MnBi₂Te₄-based systems are predicted and/or observed to show 12 different types of Hall effect [5,6], some of them are fundamentally new, such as the layer Hall effect [6]. In MnBi₂Te₄/hBN van der Waals heterostructures, a stack of n MnBi₂Te₄ films with C = 1 intercalated by hBN monolayers gives rise to a high Chern number state, characterized by C = n chiral edge modes [7], this number being as large as allowed by the van der Waals heterostructures growth technology. Concerning current challenges of this field, we will discuss the issue of the Dirac point gap in the MnBi₂Te₄ topological surface state that caused a lot of controversy. While the early experimental measurements reported on large Dirac point gaps, in agreement with ab initio calculations, a number of further studies claimed to observe a gapless dispersion of the MnBi₂Te₄ Dirac cone. A number of possible theoretical explanations of this unexpected behavior have been put forward, which we will discuss in the context of the available experimental data [8].



References

[1] M.M. Otrokov et al. Nature 576 16 (2019)

[2] M.M. Otrokov et al. Phys. Rev. Lett. 122 07202 (2019)

[3] Y. Gong et al., Chin. Phys. Lett. 36, 076801 (2019)

[4] I.I. Klimovskikh et al. npj Quantum Mater. 5 54 (2020)

[5] Y. Deng et al. Science 367 (2020) 895

[6] A. Gao et al. Nature 595 (2021) 521

[7] M. Bosnar et al. npj 2D Mater. Appl. 7 33 (2023)

[8] M. Garnica et al. npj Quantum Mater. 7 7 (2022)