Exchange Bias in Magnetic Topological Insulator Superlattices.

Jieyi Liu,Yu Yang Fredrik Liu,Barat Achinuq,Adrian Ionescu,Crispin H W Barnes,Angadjit Singh,Thorsten Hesjedal

doi:10.1021/acs.nanolett.0c01666

Abstract

Magnetic doping and proximity coupling can open a band gap in a topological insulator (TI) and give rise to dissipationless quantum conduction phenomena. Here, by combining these two approaches, we demonstrate a novel TI superlattice structure that is alternately doped with transition and rare earth elements. An unexpected exchange bias effect is unambiguously confirmed in the superlattice with a large exchange bias field using magneto-transport and magneto-optical techniques. Further, the Curie temperature of the Cr-doped layers in the superlattice is found to increase by 60 K compared to a Cr-doped single-layer film. This result is supported by density-functional-theory calculations, which indicate the presence of antiferromagnetic ordering in Dy:Bi2Te3 induced by proximity coupling to Cr:Sb2Te3 at the interface. This work provides a new pathway to realizing the quantum anomalous Hall effect at elevated temperatures and axion insulator state at zero magnetic field by interface engineering in TI heterostructures.

Highlights

Magnetic doping and proximity coupling can open a band gap in a topological insulator (TI) and give rise to dissipationless quantum conduction phenomena
Despite the ferromagnetic (FM) ordering temperatures being ∼25 K, the quantum anomalous Hall effect (QAHE) was only observed at low sub-K temperatures, which is attributed to Dirac-mass disorder,[5] i.e., the fact that the inhomogeneous spatial distribution of magnetic dopants leads to spatially varying band gap sizes
Since the size of the band gap is directly proportional to the magnetic moment in time-reversal symmetry (TRS)-broken TI materials, doping with rare earth (RE) elements such as Dy, which has a large atomic moment of up to 10.5 μB, has been considered an alternative approach to raise the QAHE temperature.[7]

Summary

Introduction

Magnetic doping and proximity coupling can open a band gap in a topological insulator (TI) and give rise to dissipationless quantum conduction phenomena.

Results

Conclusion