Unique Thickness-Dependent Properties of the van der Waals Interlayer Antiferromagnet ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ Films

Using density functional theory and Monte Carlo calculations, we study the thickness dependence of the magnetic and electronic properties of a van der Waals interlayer antiferromagnet in the two-dimensional limit. Considering ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ as a model material, we find it to demonstrate a remarkable set of thickness-dependent magnetic and topological transitions. While a single septuple layer block of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is a topologically trivial ferromagnet, the thicker films made of an odd (even) number of blocks are uncompensated (compensated) interlayer antiferromagnets, which show wide band gap quantum anomalous Hall (zero plateau quantum anomalous Hall) states. Thus, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is the first stoichiometric material predicted to realize the zero plateau quantum anomalous Hall state intrinsically. This state has been theoretically shown to host the exotic axion insulator phase.

Figure 1

(a) Atomic structure of the $R\overline{3}m$-group bulk ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ with red, green, and white balls showing Mn, Bi, and Te atoms, respectively. The paramagnetic rhombohedral unit cell is shown by black lines. (b) Calculated exchange constants $J_{0j}$ for the intralayer pair interactions as a function of the distance $r_{\mathrm{Mn}(0)-\mathrm{Mn}(j)}$ for the bulk (circles) and free-standing SL (squares). (c) 1-, 2-, and 3-SL-thick ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ films, showing an FM, compensated AFM, and uncompensated AFM orders, respectively.

Figure 2

Electronic band structures of the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ films calculated along the $\overline{K}–\overline{\mathrm{\Gamma }}–\overline{M}$ path in the 2D Brillouin zone for different thicknesses: (a) 1 SL, (b) 2 SLs, (c) 3 SLs, and (d) 4 SLs.

Figure 3

Edge electronic band structures of the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ 2-SL-thick film calculated for the (a) FM and (b) cAFM states. The regions with a continuous spectrum correspond to the 2D bulk states projected onto a 1D Brillouin zone. The edge crystal structure is shown in Supplemental Material I [37].