拓扑近藤绝缘体的低温扫描隧道显微学研究

Recently, a new kind of quantum material named topological Kondo insulators are predicted by extending the concept of topological insulator into strong correlated systems. Topological Kondo insulators also possess gapless surface states that are protected by time-reversal symmetry. Recent first-principle calculations and transport measurements suggest the typical Kondo material SmB6 or CeNiSn might be the realizations of topological non-trivial Kondo insulator. Compare to traditional topological insulator like Bi2Se3, a big advantage of SmB6 is its bulk is highly insulating, which is very favorable for the application that based on the topological surface states. SmB6 also provides us a promising platform to study the interplay between strong correlated effect and topological phenomena. However, experimental studies of topological Kondo insulators are still very limited, even the verification of their topological nature has not been completed. In this project, we plan to systematically study the electron structure of SmB6 and CeNiSn by using low temperature scanning tunneling microscopy. The properties of surface state such as E-k dispersion, Fermi surface structure and spin configuration will be investigated through quasiparticle interference. And the strong correlated nature of the system like development of Kondo screen will be investigated through variable temperature measurement. Our project will help people understand the topological phenomena in strong correlated systems and finally utilize the topological surface states.

拓扑近藤（Kondo）绝缘体是最近理论预言的，具有强关联效应的新型拓扑量子材料，是拓扑分类理论扩展到强关联体系的结果。理论计算显示一些传统的近藤材料如SmB6、CeNiSn等可能是拓扑非平凡的，它们的表面上具有无能隙的、受时间反演对称性保护的表面态。尤其是对于SmB6，它的表面态存在已经得到了输运实验的支持。而且相比传统的Bi2Se3类拓扑绝缘体，SmB6的体绝缘性更好，这为实际利用拓扑表面态提供了方便。这些材料还提供了独特的研究强关联体系能带拓扑结构的平台。目前对拓扑近藤绝缘体电子结构尤其是表面态的实验观察还很缺乏。本课题将利用极低温扫描隧道显微镜来研究SmB6、CeNiSn等材料的电子结构，考察表面准粒子散射获得表面态的信息。通过变温实验研究电子关联效应如近藤屏蔽的演化，解释拓扑表面态产生根源。本项目实施将为理解拓扑近藤绝缘体的产生机制和将来实际利用表面态提供实验基础。

拓扑近藤绝缘体是最近理论预言的，具有强关联效应的新型拓扑量子材料，是拓扑分类理论扩展到强关联体系的结果。计算显示一些传统的近藤材料如SmB6、CeNiSn等可能是拓扑非平凡的，它们的表面上具有无能隙的、受时间反演对称性保护的表面态，而目前对拓扑近藤绝缘体电子结构尤其是表面态的实验观察还很缺乏。本项目主要研究内容包括拓扑近藤绝缘体材料的生长制备、拓扑近藤绝缘体表面态的实验观察、通过变温研究拓扑近藤绝缘体中的强关联效应与表面态的关系等。通过项目实施，我们初步实现拓扑近藤绝缘体薄膜的MBE生长。我们通过ARPES测量获得了SmB6表面态存在的直接证据，并显示出其具有自旋手性因而很可能是拓扑表面态，这为理解SmB6反常的输运性质提供了依据。另外我们还观测到了关联拓扑绝缘体YbB6和中心反演非对称拓扑材料BiTeCl的表面态存在。项目共在国际SCI期刊上发表论文3篇，包括Nature Communications. 1篇，Scientific Reports 一篇，Journal of Physics: Condensed Matter 1篇，培养博士生2人。