Focused ion beam fabrication of epitaxially grown Fe(Se,Te)/Bi₂Te₃ superconductor devices

Focused-ion beam (FIB) sculpting is versatile and widely used for creating devices with micro- and nanoscale feature sizes and is applicable across a wide range of materials with diverse mechanical and chemical properties. For example, FIB has been employed to create components for superconducting devices such as Josephson junctions, which is a critical component for quantum computation platforms. Prototypical topological superconducting materials composed of epitaxial materials such as Fe(Te,Se) and Bi_₂Te_₃ present key problems where FIB may possess advantages. For example, these layered systems are chemically and mechanically sensitive while requiring small feature sizes due to the small superconducting coherence length. Here, we will present the recent fabrication of nanometer-scale weak links of Josephson junctions out of Fe(Te,Se) grown epitaxially on Bi_₂Te_₃. The critical challenge is to etch the superconductor Fe(Te,Se) while leaving the underlying topological insulator intact, which acts as the weak link in the JJ. We will discuss the effects on materials properties and device functionality as a function of beam properties such as ion species (Si++ and He+), incident energies, as well as total dose. Moreover, we will discuss the critical aspects for minimal feature size and how pushing down to the nanometer scale is critical for incorporating these materials into functional superconducting devices.