Single in situ Interface Characterization Composed of Niobium and a Selectively Grown (Bi${}_{1-x}$Sb${}_x$)${}_2$Te${}_3$ Topological Insulator Nanoribbon

Abstract

With increasing attention in Majorana physics for possible quantum bit applications, a large interest has been developed to understand the properties of the interface between a $s$-type superconductor and a topological insulator. Up to this point the interface analysis was mainly focused on in situ prepared Josephson junctions, which consist of two coupled single interfaces or to ex-situ fabricated single interface devices. In our work we utilize a novel fabrication process, combining selective area growth and shadow evaporation which allows the characterization of a single in situ fabricated Nb/$(\mathrm{B}{\mathrm{i}}_{0.15}\mathrm{S}{\mathrm{b}}_{0.85}{)}_2\mathrm{T}{\mathrm{e}}_3$ nano interface. The resulting high interface transparency is apparent by a zero bias conductance increase by a factor of 1.7. Furthermore, we present a comprehensive differential conductance analysis of our single in situ interface for various magnetic fields, temperatures and gate voltages. Additionally, density functional theory calculations of the superconductor/topological insulator interface are performed in order to explain the peak-like shape of our differential conductance spectra and the origin of the observed smearing of conductance features.

Main manuscript: 11 pages, 6 figures, Supplementary material: 10 pages, 9 figures