Progress on the antiferromagnetic topological insulator MnBi2Te4

Light-Induced Topological Phase Transition with Tunable Layer Hall Effect in Axion Antiferromagnets

The intricate interplay between light and matter provides effective tools for manipulating topological phenomena. Here, we theoretically propose and computationally show that circularly polarized light holds the potential to transform the axion insulating phase into a quantum anomalous Hall state in MnBi2Te4 thin films, featuring tunable Chern numbers (ranging up to ±2). In particular, we reveal the spatial rearrangement of the hidden layer-resolved anomalous Hall effect under light-driven Floquet engineering. Notably, upon Bi2Te3 layer intercalation, the anomalous Hall conductance predominantly localizes in the nonmagnetic Bi2Te3 layers that hold zero Berry curvature in the intact state, suggesting a significant magnetic proximity effect. Additionally, we estimate variations in the magneto-optical Kerr effect, giving a contactless method for detecting topological transitions. Our work not only presents a strategy to investigate emergent topological phases but also sheds light on the possible applications of the layer Hall effect in topological antiferromagnetic spintronics.

ARPES investigation of the electronic structure and its evolution in magnetic topological insulator MnBi2+2nTe4+3n family

In the past 5 years, there has been significant research interest in the intrinsic magnetic topological insulator family compounds MnBi2+2nTe4+3n (where n = 0, 1, 2 …). In particular, exfoliated thin films of MnBi2Te4 have led to numerous experimental breakthroughs, such as the quantum anomalous Hall effect, axion insulator phase and high-Chern number quantum Hall effect without Landau levels. However, despite extensive efforts, the energy gap of the topological surface states due to exchange magnetic coupling, which is a key feature of the characteristic band structure of the system, remains experimentally elusive. The electronic structure measured by using angle-resolved photoemission (ARPES) shows significant deviation from ab initio prediction and scanning tunneling spectroscopy measurements, making it challenging to understand the transport results based on the electronic structure. This paper reviews the measurements of the band structure of MnBi2+2nTe4+3n magnetic topological insulators using ARPES, focusing on the evolution of their electronic structures with temperature, surface and bulk doping and film thickness. The aim of the review is to construct a unified picture of the electronic structure of MnBi2+2nTe4+3n compounds and explore possible control of their topological properties.

Exploring the Epitaxial Growth Kinetics and Anomalous Hall Effect in Magnetic Topological Insulator MnBi2Te4 Films

The discovery of MnBi2Te4-based intrinsic magnetic topological insulators has fueled tremendous interest in condensed matter physics, owing to their potential as an ideal platform for exploring the quantum anomalous Hall effect and other magnetism-topology interactions. However, the fabrication of single-phase MnBi2Te4 films remains a common challenge in the research field. Herein, we present an effective and simple approach for fabricating high-quality, near-stoichiometric MnBi2Te4 films by directly matching the growth rates of intermediate Bi2Te3 and MnTe. Through systematic experimental studies and thermodynamic calculations, we demonstrate that binary phases of Bi2Te3 and MnTe are easily formed during film growth, and the reaction of Bi2Te3 + MnTe → MnBi2Te4 represents the rate-limiting step among all possible reaction paths, which could result in the presence of Bi2Te3 and MnTe impurity phases in the grown MnBi2Te4 films. Moreover, Bi2Te3 and MnTe impurities introduce negative and positive anomalous Hall (AH) components, respectively, in the AH signals of MnBi2Te4 films. Our work suggests that further manipulation of growth parameters should be the essential route for fabricating phase-pure MnBi2Te4 films.

Electric-Field Control of Spin Polarization above Room Temperature in Single-Layer A-Type Antiferromagnetic Semiconductor

Two-dimensional (2D) antiferromagnets have drawn great interest for absence of stray fields in antiferromagnetic (AFM) spintronics. However, it remains challenging to manipulate their spin polarization above room temperature for practical applications. Herein, a general strategy is reported to realize the control of spin polarization above room temperature in 2D A-type AFM semiconductors by external electric field based on first-principles calculations, exemplified by transition metal monohalide MnCl and carbide MXenes Cr₂CX₂ (X = F, Cl, OH). It shows that 100% spin polarization can be induced around Fermi level with spin splitting gap related to the spatial distribution of spin density in real space. Meanwhile, the Neél temperature of 2D MnCl and Cr₂CF₂ remains above room temperature under external electric field up to 0.6 V/Å. This study exhibits the potential for application of 2D AFM semiconductors in electric-field-controlled spintronics.