Unique thickness-dependent properties of the van der Waals interlayer antiferromagnet $\mathrm{MnBi_2Te_4}$ films (1810.05289v1)

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.

• The paper demonstrates that MnBi2Te4 films exhibit a transition from trivial ferromagnetism in a single septuple layer to compensated and uncompensated antiferromagnetic orders in even and odd layers.
• The paper employs advanced DFT and Monte Carlo simulations to uncover significant electronic bandgaps, with notable values of 107 meV in 2-SL films and 66 meV in 3-SL films.
• The paper highlights the intrinsic realization of ZPQAH states in MnBi2Te4, paving the way for axion insulator phases and potential applications in high-temperature quantum computing and spintronics.

Unique Thickness-Dependent Properties of MnBi$_2$Te$_4$ Films

The academic paper titled "Unique thickness-dependent properties of the van der Waals interlayer antiferromagnet MnBi$_2$Te$_4$ films" examines the intriguing characteristics that arise as a function of thickness in MnBi$_2$Te$_4$ films, an antiferromagnetic topological insulator (AFM TI). Through density functional theory (DFT) and Monte Carlo methods, the authors investigate the magnetic and electronic properties exhibited by these van der Waals (vdW) structures as they are reduced to the two-dimensional (2D) limit.

Methodological Approach

The paper employs advance computational techniques, specifically DFT with appropriate corrections for vdW interactions and spin-orbit coupling, as well as Monte Carlo simulations, to deduce the phase transitions and associated properties as a function of film thickness. This methodological rigor ensures an accurate description of the electronic and magnetic phenomena, offering reliable insights into the behavior of MnBi$_2$Te$_4$ thin films.

Thickness-Dependent Transitions

One key highlight of this work is the elucidation of distinct magnetic and topological transitions contingent on the number of MnBi$_2$Te$_4$ septuple layers (SLs). The authors find that:

• A single SL exhibits a topologically trivial ferromagnetic (FM) state.
• Films containing an even number of SLs display compensated antiferromagnetic (cAFM) order, while those with an odd number of SLs exhibit uncompensated AFM (uAFM) order.
• Notably, MnBi$_2$Te$_4$ is proposed as the first stoichiometric material to inherently realize zero plateau quantum anomalous Hall (ZPQAH) states, linked to the theoretically exotic axion insulator phase.

Numerical Results and Predictions

The paper reports several significant numerical findings. The electronic band structure reveals sizable bandgaps, which are particularly promising for experimental realization. For instance, in 2-SL films, the ZPQAH state is marked by a bandgap of 107 meV, a relatively large value that could enhance its stability for practical applications. Meanwhile, for the odd-numbered SL films, such as 3 SLs, a quantum anomalous Hall (QAH) state with a bandgap of approximately 66 meV is predicted.

Implications and Future Directions

The insights derived from this research have profound implications for the fields of spintronics and material science. The inherent ZPQAH states observed in MnBi$_2$Te$_4$ films are of particular interest as they offer a possible pathway to realizing axion insulators without the need for external magnetic fields or engineered heterostructures. Beyond MnBi$_2$Te$_4$, similar behaviors might be anticipated in related compounds like MnSb$_2$Te$_4$ and MnBi$_2$Se$_4$, heralding a new class of vdW materials for advanced technological applications.

Conclusion

This paper significantly advances the understanding of 2D magnetic topological insulators. By exploring MnBi$_2$Te$_4$'s thickness-dependent transitions, it lays the groundwork for future experimental studies aimed at harnessing these states for high-temperature quantum computing and other innovative applications. The research opens avenues for further exploration of vdW antiferromagnets, potentially leading to breakthroughs in AFM spintronics.