Strongly enhanced topological quantum phases in dual-surface AlO-encapsulated MnBiTe.

The topological quantum phases in antiferromagnetic topological insulator MnBiTe hold promise for next-generation spintronics, but their experimental realization has been constrained by challenges in preparing high-quality devices. In this work, we report a new wax-assisted exfoliation and transfer method that enables the fabrication of MnBiTe heterostructures with both surfaces encapsulated by AlO. This strategy strongly enhances the transport performances of the topological quantum phases in MnBiTe flakes, which is attributed to the enhancement of magnetism by the AlO layer.

Antiferromagnetic quantum anomalous Hall effect under spin flips and flops.

The interplay between nontrivial band topology and layered antiferromagnetism in MnBiTe has opened a new avenue for exploring topological phases of matter. The quantum anomalous Hall effect and axion insulator state have been observed in odd and even number layers of MnBiTe, and the quantum metric nonlinear Hall effect has been shown to exist in this topological antiferromagnet. The rich and complex antiferromagnetic spin dynamics in MnBiTe is expected to generate new quantum anomalous Hall phenomena that are absent in conventional ferromagnetic topological insulators, but experimental observations are still unknown.

Towards the quantized anomalous Hall effect in AlO-capped MnBiTe.

The quantum anomalous Hall effect in layered antiferromagnet MnBiTe harbors a rich interplay between magnetism and topology, holding a significant promise for low-power electronic devices and topological antiferromagnetic spintronics. In recent years, MnBiTe has garnered considerable attention as the only known material to exhibit the antiferromagnetic quantum anomalous Hall effect. However, this field faces significant challenges as the quantization at zero magnetic field depending critically on fabricating high-quality devices.

Direct observation of chiral edge current at zero magnetic field in a magnetic topological insulator.

The chiral edge current is the boundary manifestation of the Chern number of a quantum anomalous Hall (QAH) insulator. The van der Waals antiferromagnet MnBiTe is theorized to be a QAH in odd-layers but has shown Hall resistivity below the quantization value at zero magnetic field. Here, we perform scanning superconducting quantum interference device (sSQUID) microscopy on these seemingly failed QAH insulators to image their current distribution.

Fabrication-induced even-odd discrepancy of magnetotransport in few-layer MnBiTe.

The van der Waals antiferromagnetic topological insulator MnBiTe represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBiTe in the ground state. In this article, we demonstrate that fabrication can induce mismatched even-odd layer dependent magnetotransport in few-layer MnBiTe.

Giant nonlocal edge conduction in the axion insulator state of MnBiTe.

The recently discovered antiferromagnetic (AFM) topological insulator (TI) MnBiTe represents a versatile material platform for exploring exotic topological quantum phenomena in nanoscale devices. It has been proposed that even-septuple-layer (even-SL) MnBiTe can host helical hinge currents with unique nonlocal behavior, but experimental confirmation is still lacking. In this work, we report transport studies of exfoliated MnBiTe flakes with varied thicknesses down to the few-nanometer regime.

Direct visualization of edge state in even-layer MnBiTe at zero magnetic field.

Being the first intrinsic antiferromagnetic (AFM) topological insulator (TI), MnBiTe is argued to be a topological axion state in its even-layer form due to the antiparallel magnetization between the top and bottom layers. Here we combine both transport and scanning microwave impedance microscopy (sMIM) to investigate such axion state in atomically thin MnBiTe with even-layer thickness at zero magnetic field. While transport measurements show a zero Hall plateau signaturing the axion state, sMIM uncovers an unexpected edge state raising questions regarding the nature of the "axion state".

Helical Luttinger Liquid on the Edge of a Two-Dimensional Topological Antiferromagnet.

A boundary helical Luttinger liquid (HLL) with broken bulk time-reversal symmetry belongs to a unique topological class that may occur in antiferromagnets (AFM). Here, we search for signatures of HLL on the edge of a recently discovered topological AFM, MnBiTe even-layer. Using a scanning superconducting quantum interference device, we directly image helical edge current in the AFM ground state appearing at its charge neutral point.