Constructing heterostructures of a topological insulator (TI) with an undoped magnetic insulator (MI) is a clean and versatile approach to break the time-reversible symmetry in the TI surface states. Despite a lot of efforts, the strength of the interfacial magnetic proximity effect (MPE) is still too weak to achieve the quantum anomalous Hall effect and many other topological quantum phenomena. Recently, a new approach, “magnetic extension,” was proposed to achieve strong MPE [Otrokov et al., 2D Mater. 4, 025082 (2017)]. This approach is demonstrated effective by intercalation of the MI layer to the TI [Hirahara et al., Nano Lett. 17, 3493 (2017)]. Motivated by this proposal, here we study a magnetic extension system prepared by molecular beam epitaxial growth of MnSe thin films on a topological insulator ${\left(\mathrm{Bi},\mathrm{Sb}\right)}_2{\mathrm{Te}}_3$. Direct evidence is obtained for intercalation of the MnSe atomic layer into a few quintuple layers of ${\left(\mathrm{Bi},\mathrm{Sb}\right)}_2{\mathrm{Te}}_3$, forming either a double magnetic septuple layer (SL) or an isolated single SL at the interface, where one SL denotes a van der Waals building block consisting of B-A-B-Mn-B-A-B ($\mathrm{A}={\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$, $\mathrm{B}={\mathrm{Te}}_{1-y}{\mathrm{Se}}_y$). The two types of interfaces (namely, TI/mono-SL and TI/bi-SL) have different MPE, which is manifested as distinctively different transport behaviors. Specifically, the mono-SL induces a spin-flip transition with a sharp change at a small magnetic field in the anomalous Hall effect of the TI layers, while the bi-SL induces a spin-flop transition with a slow change at large field. Our work provides a useful platform to realize the full potential of the magnetic extension approach for pursuing novel topological physics and related device applications.

中文翻译：

---

磁性扩展拓扑绝缘子异质结构中的异常霍尔效应

使用未掺杂的磁绝缘体（MI）构造拓扑绝缘体（TI）的异质结构是一种打破TI表面状态下时间可逆对称性的干净且通用的方法。尽管付出了很多努力，但界面磁邻近效应（MPE）的强度仍然太弱，无法实现量子异常霍尔效应和许多其他拓扑量子现象。最近，提出了一种新的方法“磁性扩展”以实现强大的MPE [Otrokov等。，二维Mater。 4，025082（2017）]。MI层插入TI证明了这种方法是有效的[Hirahara等。，Nano Lett。 17，3493（2017）]。受此建议的激励，在这里我们研究由分子束外延生长MnSe薄膜在拓扑绝缘体上制备的磁扩展系统${（双，锑）}_2{特}_3$。获得了直接的证据表明MnSe原子层插入了几个五层的${（双，锑）}_2{特}_3$，在界面处形成双磁石层（SL）或隔离的单个SL，其中一个SL表示由BAB-Mn-BAB（$\mathrm{一种}={双}_{\mathrm{1个}-X}{锑}_X$， $\mathrm{乙}={特}_{\mathrm{1个}-ÿ}{硒}_{ÿ}$）。两种类型的接口（即TI / mono-SL和TI / bi-SL）具有不同的MPE，这表现为明显不同的传输行为。具体而言，在SL层的异常霍尔效应中，单SL感应在小磁场下发生急剧变化的自旋翻转跃迁，而Bi SL感应在大场上发生缓慢变化的自旋翻转跃迁。我们的工作提供了一个有用的平台，可充分发挥磁性扩展方法的潜力，以追求新颖的拓扑物理和相关设备应用。