拓扑绝缘体和磁性绝缘体的异质结和超晶格的基础研究

Topological Insulators (TIs) is a new state of matter. Its unique surface state is protected by time reversal symmetry and its electron spin is locking to the momentum. A lot of novel effects have been observed in TIs, such as dispassionless conductance, Quantum Spin Hall effect (QSH) and Quantum Anomalous Hall effect (QAH). Right now, to engineer the topological surface states, doping transition metals into the topological insulators has been widely used to form ferromagnetic TIs and to break the time reversal symmetry. But because of the low solubility of transition metals in TIs, the doping concentration is very low, and thus the Curie temperature of magnetic TIs is low. All the novel physical phenomena, including the QAH can only be observed at extremely low temperature (< 0.09 K). In this proposal, we are planning to grow topological insulator and ferromagnetic insulator heterostructures and superlattice structures using molecular beam epitaxy. Through the proximity effect at the interface, we are expecting ferromagnetic TIs with higher Curie temperature to be realized. Additionally, through the superlattice structures, the interference from the multiple quantum well structures could potentially increase the proximity effect and enhance the ferromagnetism, resulting the observation of the effects at much higher temperature.

拓扑绝缘体是一种新型的量子物质态。其表面态具有时间反演对称性的保护和自旋动量锁定，展现出来了很多非常新奇的物理现象，包括无损耗的电子输运，量子自旋霍尔效应和反常量子霍尔效应。目前研究拓扑绝缘体的表面态，通常是通过掺杂过渡金属，来实现磁性拓扑绝缘体，进而破坏表面态的时间反演对称性。但是由于过渡金属在拓扑绝缘体材料中的有限的溶解度，掺杂浓度很低，导致居里温度很低。各种新奇的物理现象，包括反常量子霍尔效应等等都只能在极低的温度下才能观察到。本项目着主要是利用分子束外延技术，来生长超高质量的拓扑绝缘体和磁性绝缘体材料的异质结构/超晶格结构。通过磁性材料的邻近效应，来形成较高居里温度的磁性拓扑绝缘体。同时通过超晶格结构，我们可以实现单个量子阱到多个量子阱的质变，放大各种界面效应(邻近效应)，进而更加容易观察到新型的物理效应。

拓扑绝缘体是一种新型的量子物质态。其表面态具有时间反演对称性的保护和自旋动量锁定，展现出来了很多非常新奇的物理现象，包括无损耗的电子输运，量子自旋霍尔效应和反常量子霍尔效应。目前研究拓扑绝缘体的表面态，通常是通过掺杂过渡金属，来实现磁性拓扑绝缘体，进而破坏表面态的时间反演对称性。但是由于过渡金属在拓扑绝缘体材料中的有限的溶解度，掺杂浓度很低，导致居里温度很低。各种新奇的物理现象，包括反常量子霍尔效应等等都只能在极低的温度下才能观察到。本项目主要是利用分子束外延技术，来生长超高质量的拓扑绝缘体和磁性绝缘体材料的异质结构/超晶格结构。通过磁性材料的邻近效应，来形成较高居里温度的磁性拓扑绝缘体。同时在本项目中实现了原位观察到了磁性掺杂导致拓扑绝缘体表面态带隙打开的现象，证实了铁磁性的存在。另一方面申请人研究的基于本征拓扑绝缘体和有机材料的异质结构材料在宽带光电器件探测和自旋电子器件方面具有巨大的应用前景。并在项目的支持下，申请人合计在重要的国际期刊上发表了21篇SCI学术论文。