Spin-flop transition and Zeeman effect of defect-localized bound states in the antiferromagnetic topological insulator MnBi_(2)Te_(4)

The correlation of surface impurity states with the antiferromagnetic ground states is crucial for understanding the formation of the topological surface state in the antiferromagnetic topological insulators MnBi_(2)Te_(4).By using low-temperature scanning tunneling microscopy and spectroscopy,we observed a localized bound state around the Mn-Bi antisite defect at the Teterminated surface of the antiferromagnetic topological insulator MnBi_(2)Te_(4).When applying a magnetic field perpendicular to the surface(Bz)from–1.5 to 3.0 T,the bound state shifts linearly to a lower energy with increasing Bz,which is attributed to the Zeeman effect.Remarkably,when applying a large range of Bz from–8.0 to 8.0 T,the magnetic field induced reorientation of surface magnetic moments results in an abrupt jump in the local density of states(LDOS),which is characterized by LDOSchange-ratio■quantitatively.Interestingly,two asymmetric critical field,–2.0 and 4.0 T determined by the two peaks in■are observed,which is consistent with simulated results according to a Mills-model,describing a surface spin flop transition(SSF).Our results provide a new flatform for studying the interplay between magnetic order and topological phases in magnetic topological materials.

Magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulators

Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator Mn Bi2Te4.We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment,Kerr and Faraday effects occur.Under perpendicular electric field,antiferromagnetic topological insulators(AFMTI)show sharp peaks at the interband transition threshold,whereas trivial insulators show small adjacent positive and negative peaks.Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators.We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr(Faraday)angles and vanishing ellipticity.Under external magnetic moment,AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity.For the qualitative behaviors,AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change.These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.

Magnetic Proximity Effect in an Antiferromagnetic Insulator/Topological Insulator Heterostructure with Sharp Interface

We report an experimental study of electron transport properties of MnSe/(Bi,Sb)_2Te_3 heterostructures,in which MnSe is an antiferromagnetic insulator,and(Bi,Sb)_2Te_3 is a three-dimensional topological insulator(TI).Strong magnetic proximity effect is manifested in the measurements of the Hall effect and longitudinal resistances.Our analysis shows that the gate voltage can substantially modify the anomalous Hall conductance,which exceeds 0.1 e^(2)/h at temperature T=1.6 K and magnetic field μ_0H=5 T,even though only the top TI surface is in proximity to MnSe.This work suggests that heterostructures based on antiferromagnetic insulators provide a promising platform for investigating a wide range of topological spintronic phenomena.