Influence of defects on electronic property of Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te/Pb heterostructure

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 in 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 important 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 Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te/Pb. The Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te 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 Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te films are detected in situ by using low-temperature scanning tunneling microscopy and spectroscopy. The differential conductance tunneling spectra show that the minima of d<i>I</i>/d<i>V</i> spectra taken in the areas near the film edge, the grain boundary and the dislocation of Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te grown on Pb can be significantly changed to the energy very close to the Fermi level or even about –0.2 eV below the Fermi level, whereas the minima of d<i>I</i>/d<i>V</i> spectra taken in the areas far away from the defects are always at about 0.2 eV above the Fermi level. It indicates that these quasi one-dimensional defects, rather than Pb alloying, play an important role in modifying electronic property of the Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Te/Pb heterostructure. Moreover, the Pb alloying will suppress the formation of zero-energy peak in the vortex. These results are expected to develop the new methods that do not require doping or alloying for the Fermi-level tuning of the SnTe-type topological superconducting devices.