Observation of Magnetism-Induced Topological Edge State in Antiferromagnetic Topological Insulator MnBi₄Te₇

Abstract

Breaking time reversal symmetry in a topological insulator may lead to quantum anomalous Hall effect and axion insulator phase. MnBi4Te7 is a recently discovered antiferromagnetic topological insulator with TN ~12.5 K, which is constituted of alternatively stacked magnetic layer (MnBi2Te4) and non-magnetic layer (Bi2Te3). By means of scanning tunneling spectroscopy, we clearly observe the electronic state present at a step edge of a magnetic MnBi2Te4 layer but absent at non-magnetic Bi2Te3 layers at 4.5 K. Furthermore, we find that as the temperature rises above TN, the edge state vanishes, while the point defect induced state persists upon temperature increasing. These results confirm the observation of magnetism induced edge states.Our analysis based on an axion insulator theory reveals that the nontrivial topological nature of the observed edge state.

Imaging the Breakdown and Restoration of Topological Protection in Magnetic Topological Insulator MnBi2Te4

“…We have included more dI/dV maps at other voltage bias, see Figure S7, Supporting Information to demonstrate the decoupled edge channel in the exchange gap. We must point out that the spectral intensity along the edge in Figure 2b seems to be disconnected, which has been also observed in previous reports on topological edge states of MnBi 2 Te 4 , [34] its related heterostructure with Bi 2 Te 3 , [35] as well as the 2D topological insulator WTe 2 . [36] It may arise due to local roughness and structural disorder along the edge.…”

Ferromagnetic Layers in a Topological Insulator (Bi,Sb)2Te3 Crystal Doped with Mn

“…However, the system can be switched to the QAH regime only in the case of ultrathin flakes containing an odd number of SLs, since such switching requires ferromagnetic ordering of magnetic moments. Another way to turn MnBi 2 Te 4 to the ferromagnetic TI state is by embedding Bi 2 Te 3 quintuple layers (QLs) between the SLs, which gives rise to MnBi 4 Te 7 , − MnBi 6 Te 10 , and MnBi 8 Te 13 structures, with only the last one being a ferromagnetic TI in bulk . In very dilute crystals Mn impurities mostly concentrate within the SLs between the bunches of QLs …”

Engineering Gapless Edge States from Antiferromagnetic Chern Homobilayer

“…Magnetic topological insulators (TIs) have attracted tremendous attention as a focal point in condensed matter physics. , A typical example is the Chern insulator (CI) characterized by the quantum anomalous Hall effect (QAHE) in two-dimensional (2D) ferromagnets. − A CI is well-known to be distinguished by the quantized anomalous Hall conductance, i.e., integer Chern number scriptC , and the gapless chiral edge states with great potential for investigating novel quantum phenomena and the future design of dissipationless spintronic devices. − Currently, explorations into the realm of magnetic TIs have expanded to so-called antiferromagnetic (AFM) TIs, the concept of which was indeed first proposed by stacking CI layers with opposite magnetization directions . In three dimensions, AFM TIs have been experimentally confirmed in the MnBi 2 Te 4 family with gapless helical surface states, revealing remarkable properties such as the axion state, a quantized magnetoelectric effect, and a type II magnetic Weyl semimetal. − The gapless edge states are robust under significant scattering and maintain the quantum dissipation-free transport, offering new opportunities for novel topological quantum device applications in the fields of spintronics and nanoscience. − However, in 2D antiferromagnets, the material realization of a nontrivial topology with gapless helical edge states has been elusive so far, and it would be of crucial significance to make a bridge between CIs and 2D AFM topological states. − …”