单体Bi2Se3纳米片拓扑超导体的电输运性质研究

Because of proximity effect, a thin layer of the surface of topological insulator in contact with s-wave superconductor can be induced into topological superconductor. With the polarization of the spin in surface states of topological insulator, the cooper pairs behave like p-wave superconductor. The long searched Majorana Fermion is supposed to exist in the vortex of p-wave superconductor. In this project, we plan to use vaccum projection method with ultra-fast valve to trap one single Bi2Se3 nano flake of 50nm length and 15nm thickness onto the nanogap of 40nm between two aluminum electrodes in order to make a Josephson junction. Next we plan to research the electronic transport of 3D topological insulator in high quantum confinement condition, and the effect of electric field and magnetic field on the tunneling electronic spectroscopy. Furthermore, we plan to induce the Bi2Se3 nano flake into topological superconductor below the transit temperature of aluminum. The superconductor energy gap can be confirmed by measuring the tunneling supercurrent through the Josephson junction, and the effect of electric field will be studied. Under the magnetic field the Zero Bias Conductance Peak will be searched to show the track of Majorana fermion.

在临近效应下，三维拓扑绝缘体和s波超导体的接触部分会被诱导出一个具有超导性质的拓扑超导体薄层。由于拓扑绝缘体表面态的自旋极化特性，拓扑超导体中的库珀对表现为p波超导态。而长久以来一直被科学家寻找的Majorana费米子被认为有可能存在于P波超导体中的磁漩涡中。本项目计划利用超快阀门真空喷射法将粒径50纳米厚度15纳米的Bi2Se3纳米片单体与一对间距40nm的铝电极相连接，建立约瑟夫森结。在此基础上进行高量子限域环境下三维拓扑绝缘体表面态的电输运研究，并研究电场和磁场的调制作用对电子隧穿谱的影响。进而在超导转变温度下对Bi2Se3纳米片进行拓扑超导体的诱导，测量约瑟夫森结中的隧穿超导电流来确认超导能隙的存在并利用栅极电场进行调制观测其响应情况。最后尝试在磁场下观测零偏压电导峰的存在，以探索Majorana费米子的线索。

本项目旨在研究Bi2Se3纳米片在高量子限域条件下的电输运性质。其最终目的是为了实现小尺寸Bi2Se3纳米片的单体捕捉和电输运测量。在推进研究过程中，我们主要做了4个方面的工作：（1）为了提高Bi2Se3纳米片捕捉效率，重新设计了纳米裂隙两侧的电极图案，利用离子束蚀刻与光刻技术的结合，制作了一种超高长宽比的纳米裂隙电极，预期可以将纳米物体在电极间的捕捉效率提高10倍以上。（2）为了更好的理解Bi2Se3纳米片在硅芯片上的电输运状态，利用第一性计算原理，对Bi2Se3/SiO2接触在空气中环境下的能级分布进行了计算。（3）由于接触电阻在Bi2Se3纳米片的捕捉过程中的所起的作用，对Bi2Se3氧缺陷对接触电阻的影响进行了一系列研究。（4）依据Klein隧穿原理，在施加高势垒的条件下，对拓扑绝缘体与金属导体间的电子隧穿率进行了计算，其结果有可能被应用于一种新的自旋极化电子流注入系统。