Dirac Surface States in Intrinsic Magnetic Topological Insulators EuSn2As2 and MnBi2nTe3n+1

Hang Li,Tian Qian,Hong Ding,Takeshi Kondo,Yi Liu,Peng Zhang,Shik Shin,Jiajun Li ,Yuanfeng Xu ,Hechang Lei ,Shangjie Tian ,Yaobo Huang ,Jierui Huang ,Guobin Zhang ,Zhicheng Rao ,Wanling Liu ,Jun Gao ,Shangyu Gao ,Shaofeng Duan ,Wenhui Fan ,Dayu Yan ,Hongming Weng ,Kejia Zhu ,Youguo Shi ,Yuliang Li ,Zhengtai Liu ,Wentao Zhang

doi:10.1103/physrevx.9.041039

Abstract

In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. In despite of intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by combining first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments, we have revealed that EuSn2As2 is an antiferromagnetic TI with observation of Dirac SSs consistent with our prediction. We also observe nearly gapless Dirac SSs in antiferromagnetic TIs MnBi2nTe3n+1 (n = 1 and 2), which were absent in previous ARPES results. These results provide clear evidence for nontrivial topology of these intrinsic magnetic TIs. Furthermore, we find that the topological SSs show no observable changes across the magnetic transition within the experimental resolution, indicating that the magnetic order has quite small effect on the topological SSs, which can be attributed to weak hybridization between the localized magnetic moments, from either 4f or 3d orbitals, and the topological electronic states. This provides insights for further research that the correlations between magnetism and topological states need to be strengthened to induce larger gaps in the topological SSs, which will facilitate the realization of topological quantum phenomena at higher temperatures.

Highlights

Time-reversal symmetry plays a key role in topological quantum states of matter
A previous study reveals that EuSn2As2 undergoes a transition from a paramagnetic (PM) phase to an AFM phase around 25 K [41], which is consistent with our measurements in Figs. 1(b) and 1(c)
When the magnetic fields are perpendicular to the c axis, the susceptibility χðTÞ in Fig. 1(b) shows an upturn below 10 K, and the isothermal magnetization MðHÞ at 2 K in Fig. 1(c) increases rapidly at low fields, indicating an in-plane ferromagnetic component probably due to canting of the magnetic moments

Summary

Introduction

Time-reversal symmetry plays a key role in topological quantum states of matter. The earliest discovered topological insulator (TI), the Chern insulator with the integer quantum Hall effect, requires breaking the time-reversal symmetry [1,2,3]. The thinking and research on timereversal symmetry in condensed matter systems directly led to the discovery of time-reversal-invariant (TRI) Z2 TIs with the quantum spin Hall effect [4,5,6,7]. The introduction of magnetism into the Z2 TIs can produce more exotic topological quantum phenomena, such as the quantum anomalous Hall effect [8,9,10,11,12,13,14], axion insulator states [15,16,17,18,19,20,21], and chiral Majorana fermions [22]. A direct solution to avoid disorder is to seek for intrinsic magnetic TIs, which have magnetic order in the stoichiometric compositions

Methods

Results

Conclusion