A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling

Abstract

Magnetic topological insulators provide an important materials platform to explore emergent quantum phenomena such as the quantized anomalous Hall (QAH) effect, Majorana modes and the axion insulator state, etc. Recently, MnBi2Te4 was discovered to be the first material realization of a van der Waals (vdW) antiferromagnetic topological insulator (TI). In the two-dimensional (2D) limit, at a record high temperature of 4.5 K, MnBi2Te4 manifests the QAH effect in the forced ferromagnetic state above 12 T. To realize the QAH effect at lower fields, it is essential to search for magnetic TIs with lower saturation fields. By realizing a bulk vdW material MnBi4Te7 with alternating [MnBi2Te4]and [Bi2Te3] layers, we suggest that it is ferromagnetic in plane but antiferromagnetic along the c axis with a small out-of-plane saturation field of ~ 0.22 T at 2 K. Our angle-resolved photoemission spectroscopy and first-principles calculations further demonstrate that MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively. Therefore, MnBi4Te7 provides a new material platform to investigate emergent topological phenomena associated with the QAH effect at much lower magnetic fields in its 2D limit.

Universal gapless Dirac cone and tunable topological states in (MnBi2Te4)m(

“…Two branches of the dispersion intersect each other at a single Dirac point, showing the gapless nature of the TSS. This is in sharp contrast to the earlier reports of a magnetic order induced surface gap in the order of hundred-meVs in both MnBi2Te4 [2,4,9,17] and MnBi4Te7 [14,15]. On the contrary, our results are consistent with the recent observation of a gapless TSS in MnBi2Te4 [32][33][34][35].…”

“…In the newly discovered magnetic topological insulator MnBi2Te4 [1][2][3][4][5][6][7][8], both axion insulator state and quantized anomalous Hall effect (QAHE) have been observed by tuning the magnetic structure [9][10][11]. The related (MnBi2Te4)m(Bi2Te3)n heterostructures with increased tuning knobs, are predicted to be a more versatile platform for exotic topological states [12][13][14][15][16]. Here, we report angle-resolved photoemission spectroscopy (ARPES) studies on a series of the heterostructures (MnBi2Te4, MnBi4Te7 and MnBi6Te10).…”

“…(MnBi2Te4)m(Bi2Te3)n heterostructures represent a closely related but more complex system, in which both MnBi2Te4 and Bi2Te3 layers are essential building blocks (Fig. 1b,c) [1,2,[14][15][16]. The reduced interlayer antiferromagnetic exchange coupling (due to the nonmagnetic Bi2Te3 layers) facilitates the magnetic manipulation [14][15][16], and two distinct building blocks provide an additional knob to tune the topological states by different stackings of the van der Waals layers 3 ( Fig.…”

“…1b,c). In this sense, the (MnBi2Te4)m(Bi2Te3)n heterostructures are predicted to be a more versatile playground for realizing exotic topological states and topological phase transitions [14][15][16].…”

Electronic States and Magnetic Response of MnBi2Te4 by Scanning Tunneling Microscopy and Spectroscopy

“…Our findings shed important lights on better design of magnetic topological insulators. To dilute the magnetic dopant, one efficient way is to add buffer layers between MnBi 2 Te 4 , which has been recently realized in MnBi 4 Te 7 (39)(40)(41). Another inspiration is the possibility to fine tune magnetic order in related materials.…”