Background
Josephson junctions turn to be the key building block to realize superconducting devices and more recently artificial atoms and superconducting qubits. In most cases, the weak link to obtain the Josephson junction is realized by an amorphous insulating barrier (AlOx), a diffusive normal metal or a short constriction. In this research topic, we realize and study a semiconducting (Ge) weak link enabling control of carrier density and tunneling rates. In the very active field of hybrid superconducting devices, such a semiconductor weak link can give rise to novel physical effects and open ways to a number of applications.
Transport properties
Up to now, we were able to study quantum transport on several monolithic Al-Ge-Al and AlGe/Si core/shell-Al heterostructures based on bottom‐up grown nanowires. An electrostatic gate coupled to the nanowire allows the transport regime through the Ge segment to be tuned.
For ultra-scaled monolithic Al–Ge–Al nanowire heterostructures, we have demonstrated the ability to tune the Ge device from completely insulating, through a single-hole-filling quantum dot regime, to a supercurrent regime, resembling a Josephson field effect transistor with a maximum critical current of 10 nA at a temperature of 390 mK. For ultra-scaled Al-Ge/Si-Al nanowire heterostructures, we have shown quantification of the conductance.
Potential applications
These results reveal a promising Ge-based architecture for hybrid superconductor– semiconductor devices for the study of Majorana zero modes and key components of quantum computing such as gatemons or gate tunable superconducting quantum interference devices.
