Cécile NAUD, Quantum transport in monolithic crystalline Al/Ge nanowire heterostructures

Cécile NAUD, Institut Néel, Grenoble

Superconductor-semiconductor-superconductor hybrid junctions have great potential for the realization of topological superconducting systems as well as gate-tunable superconducting quantum bits.  Crucial to their successful application is the quality and reproducibility of the semiconductor-superconductor interface.

Recently, a new method to obtain hybrid junctions has been established by our collaborators in Vienna. By employing a selective, thermally induced Al-Ge substitution process, monolithic Al-Ge-Al nanowire heterostructures can be achieved. These unique hybrid junctions feature crystalline quasi-one-dimensional Al leads which are connected to crystalline Ge segments by near atomically abrupt interfaces [1]. To investigate their transport properties, the nanowire junctions are integrated into a back-gated field effect transistor architecture.

In this presentation, I will show the very low temperature transport properties of ultra-scaled Al-Ge-Al nanowire heterostructures. In particular, I will show the ability to tune through a gate the Ge segment from a completely insulating regime, through a single hole quantum dot regime to a superconducting regime resembling a Josephson field effect transistor. In this last regime, the transparency of the interface is up to 95 %. The results presented will demonstrate the potential of these novel germanium nanowire based superconductor-semiconductor hybrid junctions as quantum devices.

[1] K. El. Hajraoui, A. Luong, E. Robin, F. Brunbauer, C. Zeiner, A. Lugstein, P. Gentile, J.L. Rouviere, M. Den Hertog, “In-situ TEM analysis of aluminum – germanium nanowire solid-state reaction” Nano Lett. 19 5 2897 (2019).