Unique thickness-dependent properties of the van der Waals interlayer antiferromagnet $\mathrm{MnBi_2Te_4}$ films

TL;DR

This study reveals how the magnetic and topological properties of MnBi2Te4 films vary with thickness, showing transitions from trivial ferromagnets to quantum anomalous Hall states and axion insulators, using computational methods.

Contribution

It predicts the thickness-dependent magnetic and topological phases of MnBi2Te4, including the intrinsic realization of the zero plateau quantum anomalous Hall state.

Findings

Single septuple layer is a trivial ferromagnet.

Odd layers exhibit quantum anomalous Hall effect.

Even layers show zero plateau quantum anomalous Hall state.

Abstract

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 $\mathrm{MnBi_2Te_4}$ 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 $\mathrm{MnBi_2Te_4}$ is a topologically trivial ferromagnet, the thicker films made of an odd (even) number of blocks are uncompensated (compensated) interlayer antiferromagnets, which show wide bandgap quantum anomalous Hall (zero plateau quantum anomalous Hall) states. Thus, $\mathrm{MnBi_2Te_4}$ 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.