Hard-gap spectroscopy in a self-defined mesoscopic InAs/Al nanowire Josephson junction

Superconductor-semiconductor-nanowire hybrid structures can serve as versatile building blocks to realize Majorana circuits or superconducting qubits based on quantized levels such as Andreev qubits. For all these applications, it is essential that the superconductor-semiconductor interface is as clean as possible. Furthermore, the shape and dimensions of the superconducting electrodes need to be precisely controlled. We fabricated self-defined InAs/Al core-shell nanowire junctions by a fully in-situ approach, which meet all these criteria. Transmission electron microscopy measurements confirm the sharp and clean interface between the nanowire and the in-situ deposited Al electrodes that are formed by means of shadow evaporation. Furthermore, we report on tunnel spectroscopy, gate, and magnetic field-dependent transport measurements. The achievable short junction lengths, the observed hard gap, and the magnetic field robustness make this hybrid structure very attractive for applications that rely on a precise control of the number of subgap states, like Andreev qubits or topological systems