Boosting Transparency in Topological Josephson Junctions via Stencil Lithography

Abstract

Hybrid devices comprised of topological insulator (TI) nanostructures in proximity to s-wave superconductors (SC) are expected to pave the way towards topological quantum computation. Fabrication under ultra-high vacuum conditions is necessary to attain high quality of TI-SC hybrid devices, because the physical surfaces of V-VI three-dimensional TIs suffer from degradation at ambient conditions. Here, we present an in-situ process, which allows to fabricate such hybrids by combining molecular beam epitaxy and stencil lithography. As-prepared Josephson junctions show nearly perfect interface transparency and very large $I_CR_N$ products. The Shapiro response of radio frequency measurements indicates the presence of gapless Andreev bound states, so-called Majorana bound states.

An EDX analysis showed a high Sb contribution in the TI thin films. The chip investigated turned out to be a (Bi0.06Sb0.94)2Te3 TI thin film instead of Bi2Te3. However, the main results of our work remain unchanged. The high Sb concentration most importantly changes the position of the Fermi level with respect to the Dirac point. The effect of this shifting is also discussed in the new version