Intertwined Topological and Magnetic Orders in Atomically Thin Chern Insulator MnBi₂Te₄

Abstract

MnBi2Te4, a van der Waals magnet, is an emergent platform for exploring Chern insulator physics. Its layered antiferromagnetic order was predicted to enable even–odd layer number dependent topological states. Furthermore, it becomes a Chern insulator when all spins are aligned by an applied magnetic field. However, the evolution of the bulk electronic structure as the magnetic state is continuously tuned and its dependence on layer number remains unexplored. Here, employing multimodal probes, we establish one-to-one correspondence between bulk electronic structure, magnetic state, topological order, and layer thickness in atomically thin MnBi2Te4 devices. As the magnetic state is tuned through the canted magnetic phase, we observe a band crossing, i.e., the closing and reopening of the bulk band gap, corresponding to the concurrent topological phase transition in both even- and odd-layer-number devices. Our findings shed new light on the interplay between band topology and magnetic order in this newly discovered topological magnet.

Direct visualization of edge state in even-layer MnBi2Te4 at zero magnetic field

“…The existence of a metallic bulk state during the transition is corroborated by our bulk transport measurement as well (see supplementary information S3). The evolution of bulk conductivity as a function of magnetic field was reported in another work with similar results 28 .…”

Intrinsic magnetic topological insulators

“…Recently, two independent studies reported unusual layer-dependent magnetic properties in MBT devices, 56 , 57 observing anomalous magnetic hysteresis loops in polar reflective magnetic circular dichroism spectroscopy results 56 and anomalous Hall curves in even-layer MBT. 57 More intriguingly, Ovchinnikov et al . 57 found that the hysteresis loop near zero magnetic field vanished for an odd-layer device in the AFM state.…”

“… 57 More intriguingly, Ovchinnikov et al . 57 found that the hysteresis loop near zero magnetic field vanished for an odd-layer device in the AFM state. Actually, most device samples in experiments are inevitably affected by various factors during device fabrication process and measurements, including sample quality and oxidation.…”

Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale

“…Furthermore, upon applying a magnetic field to control the arrangement of the interlayer spins in MnBi2Te4, the states of QAH insulators and axion insulators become interchanged [11][12][13][14][15][16][17][18][19][20]. Axion insulators and Chern insulators have recently been realized in mechanically exfoliated MnBi2Te4 flakes [12,[21][22][23], but such flakes are fragile and have small and irregular shapes, thus preventing the large-scale fabrication of devices that utilize the QAH effect. Moreover, the fabrication of MnBi2Te4 flakes requires heating to a high temperature, which readily causes high-density intrinsic defects.…”