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SnTe类拓扑晶体绝缘体发生超导转变后，在其单个磁通涡旋中能够形成受晶体对称性保护的多重Majorana零能模．这种奇特的性质能够降低多个Majorana零能模之间相互作用的难度．最近多重Majorana零能模存在的实验证据已在SnTe/Pb超导异质结单个磁通涡旋中被观测到．SnTe是一种非常p型的半导体材料，如何调控其电子性质，在分辨和操控Majorana零能模方面具有重要研究意义．本文利用分子束外延技术在Si (111)衬底生长的Pb (111)薄膜上制备了Sn1-xPbxTe薄膜，并且通过扫描隧道显微镜研究了薄膜边缘、畴界以及位错对其电子态的影响．扫描隧道显微镜的微分电导谱显示，在薄膜边缘、畴界以及位错附近，Sn1-xPbxTe电子态相对于费米能级的位置能够发生显著改变，载流子类型能从p型转变到n型．在远离这些缺陷的区域，Pb含量对Sn1-xPbxTe的费米能级的影响不显著，但是过多的Pb含量会抑制磁通中零能峰的形成．该研究将为基于SnTe类材料的拓扑超导器件的设计提供新的思路．SnTe-type topological crystalline insulators (TCIs) possess multiple Dirac-like topological surface states under the mirror-symmetry protection. Superconducting SnTe-type TCIs are predicted to form multiple Majorana zero modes (MZMs) in a single magnetic vortex. For the spatially isolated MZMs, there is only one MZM in a single vortex at surface. However, experimental demonstration of coupling the two isolated MZMs by changing wire length or intervortex distance is very challenging. For the multiple MZMs, two or more MZMs can coexist together in a single vortex. Thus, the novel property is expected to significantly reduce the difficulty of producing hybridization between MZMs. Recently, the experimental evidence for multiple MZMs has been observed in a single vortex of the superconducting SnTe/Pb heterostructure. However, SnTe is a heavily p-type semiconductor which is very difficult to induce the p-type to n-type transition via doping or alloying. The study on the Fermi-level tuning of SnTe-type TCIs is critical for detecting and manipulating multiple MZMs. In this work, we report the influence of defects such as film edge, grain boundary and dislocation on the electronic property of Sn1-xPbxTe/Pb. The Sn1-xPbxTe films are prepared on the Pb (111) films grown on the Si (111) substrate by the molecular beam epitaxial technology. The structural and electronic properties of the Sn1-xPbxTe films are detected in situ by using low-temperature scanning tunneling microscopy and spectroscopy. The differential conductance tunneling spectra show that the minima of dI/dV spectra taken at the areas near the film edge, the grain boundary and the dislocation of Sn1-xPbxTe grown on Pb can be significantly changed to the energy very closed to the Fermi level or even about -0.2 eV below the Fermi level, whereas the minima of dI/dV spectra taken at the areas far away from the defects are always at about 0.2 eV above the Fermi level. It indicates that not Pb alloying but these quasi one-dimensional defects play an important role in the modification of electronic property in the Sn1-xPbxTe/Pb heterostructure. Moreover, the Pb alloying will suppress the formation of zero-energy peak in the vortex. These results are expected to develop the method of the Fermi-level tuning without need of doping or alloying for the SnTe-type topological superconducting device.
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Keywords:
- Topological crystalline insulator /
- Defect /
- Superconducting heterostructure /
- Scanning tunneling microscope
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