Abstract
Topological insulators (TIs) provide intriguing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. The combination of topological properties and magnetic order can lead to new quantum states including the quantum anomalous Hall effect that wasfirst experimentally realized in Cr-doped (Bi,Sb)2 Te3 films. Since magnetic doping can introduce detrimental effects, requiring very low operational temperatures, alternative approaches are explored. Proximity coupling to magnetically ordered systems is an obvious option, with the prospect to raise the temperature for observing the various quantum effects. Here, an overview of proximity coupling and interfacial effects in TI heterostructures is presented, which provides a versatile materials platform for tuning the magnetic and topological properties of these exciting materials. An introduction is first given to the heterostructure growth by molecular beam epitaxy and suitable structural, electronic, and magnetic characterization techniques. Going beyond transition-metal-doped and undoped TI heterostructures, examples of heterostructures are discussed, including rare-earth-doped TIs, magnetic insulators, and antiferromagnets, which lead to exotic phenomena such as skyrmions and exchange bias. Finally, an outlook on novel heterostructures such as intrinsic magnetic TIs and systems including 2D materials isgiven.
Highlights
Introduction of thequantum anomalous Hall effect (QAHE) was not reported until 2013, when transport in 3D topological insulators (TIs) doped with magnetic impuri-Quantum transport phenomena such as giant magnetore- ties was studied
We have given a broad overview of different aspects of magnetic topological insulator heterostructures, covering their growth and structure, their electronic and magnetic properties and most common characterization techniques, followed by an illustration of QAH insulators, magnetic insulators (MIs)/TI heterostructures, RE-doped TI materials, exchange-biased heterostructures, and heterostructures hosting skyrmions or showing the topological Hall effect (THE)
The prerequisites for QAH insulators are: i) a strong spin–orbit coupling (SOC) that leads to the formation of linearly dispersing surface states, and ii) magnetic order that induces a gap at the Dirac point
Summary
We will focus in this review on the established 3D TIs in the (Bi,Sb)2(Se,Te) family of solid solutions, most prominently Sb2Te3, Bi2Te3, and Bi2Se3. Much of the knowledge of this materials class is connected to their practical use as thermoelectric materials in cooling devices and generators since the late 1950s,[37] owing to their large room temperature figure-of-merit and the ability to achieve n- and p-type materials in the solid solution series.[38] Further, in the context of engineered TI heterostructures, we will restrict ourselves to the most versatile growth method, that is, molecular beam epitaxy (MBE). Apart from MBE, it is worth mentioning that magnetron sputtering, which is a more industry-friendly deposition method, has been proven successful in the growth of TI films and heterostructures, including BixSe1−x/Co20Fe60B20 and SmB6.[39,40]
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