Two types of zero Hall phenomena in few-layer MnBi$_2$Te$_4$

Abstract

The van der Waals antiferromagnetic topological insulator MnBi$_2$Te$_4$ represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Despite the realization of several quantized phenomena, such as the quantum anomalous Hall effect and the axion insulator state, the recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBi$_2$Te$_4$ in the ground state. Here, we demonstrate the existence of two distinct types of zero Hall phenomena in few-layer MnBi$_2$Te$_4$. In addition to the robust zero Hall plateau associated with the axion insulator state, an unexpected zero Hall phenomenon also occurs in some odd-number-septuple layer devices. Importantly, a statistical survey of the optical contrast in more than 200 MnBi$_2$Te$_4$ reveals that such accidental zero Hall phenomenon arises from the reduction of effective thickness during fabrication process, a factor that was rarely noticed in previous studies of 2D materials. Our finding not only resolves the controversies on the relation between magnetism and anomalous Hall effect in MnBi$_2$Te$_4$, but also highlights the critical issues concerning the fabrication and characterization of devices based on 2D materials.Comment: 21 pages, 4 figure