Bi2Se3超薄薄膜在S波超导邻近效应下的拓扑性质研究

项目名称： Bi2Se3超薄薄膜在S波超导邻近效应下的拓扑性质研究

项目编号： No.11504084

项目类型： 青年科学基金项目

立项/批准年度： 2016

项目学科： 数理科学和化学

项目作者： 曹杰

作者单位： 河海大学

项目金额： 20万元

中文摘要： 三维拓扑绝缘体是一种同时具有绝缘体态和手征半金属表面态的三维材料，这种物质态已经在Bi2Se3等材料中被实验所证实。2008年傅亮教授等学者提出，可以在Bi2Se3的表面，通过超导的邻近作用引入S波超导配对，构建出无自旋的手征P波超导体。这一理论也被之后的实验所证实。目前的理论与实验工作都要求Bi2Se3薄膜具有一定的厚度，否则手征半金属态就会由于上下表面态之间的耦合受到破坏。而我们感兴趣的正是这种Bi2Se3超薄薄膜－S波超导体系统中的准粒子行为。由于手征半金属表面态的缺失，原本的P波超导有效哈密顿量不再成立。我们希望通过扩大系统的维度，在哈密顿量中同时考虑上下表面的贡献以及它们之间的耦合作用，在引入S波超导配对之后，可以变换成有效的自旋手征P波超导哈密顿量。这里的“自旋”并不是真正的自旋，而是由上下表面构成的赝自旋，我们期望能找到一些不同寻常的性质，比如奇异的Majorana费米子等。

中文关键词： 拓扑绝缘体薄膜；Majorana费米子；表面态；P波超导；约瑟夫森结

英文摘要： Three dimensional topological insulator is a special kind of material with both bulk insulating gap and chiral semi-metal surface state. This new topological phase of mater is experimentally comfirmed in Bi2Se3, Bi2Te3 and Sb2Te3. In 2008, perfessor Fu Liang proposed that, one can construct a spinless chiral P-wave superconductor when a S-wave superconductor is deposited on the surface of Bi2Se3. After his first theoratical proposal, many theoratical and experimental researches have focused on the behavior of a single chiral surface state of Bi2Se3 film while S-wave cooper pairs are induced due to the proximity effect. This requires that Bi2Se3 film should be relatively thick since the coupling of the two surfaces states can break the chirallity of the surface states. However, when the thickness of Bi2Se3 film is below the critical value, the origional proposal of the hamiltonian of spinless chiral P-wave superconductor is invalid since the chirallity of the surface states is broken. We are interested in the behavior of elementary excitations in this case, i.e, Bi2Se3 ultra-thin film -- S wave superconductor heterostructure. We want to include the two surfaces and the coupling between them simultaneously, by expanding the dimention of the Hilbert space. In this new space, we might be able to construct a hamiltonian of spinfull chiral P-wave supercondutor by performing unitary transformation when S-wave cooper pairs are introduced. We have to emphasize that this “spin” is not a real spin of electron, it is a pseudo spin made by the degree of the two surface states. Hence, we expect to find some extraodinary properties in this system, such as novel Majorana fermions.

英文关键词： topological insulator thin film;Majorana fermion;surface state;P-wave superconductor;Josephson junction