If a semiconductor nanowire is contacted by two superconducting electron is close proximity a Josephson supercurrent can be observed.
The the tranport can be described in the framework of phase-coherent Andreev reflection. In an Andreev reflection process, an electron impinging on a normal conductor/superconductor interface is retroreflected as a hole, while creating a Cooper pair in the superconductor. The Cooper pairs carry the Josephson supercurrent. The small dimensions of the nanowire allow to investigate confinement effects in the transport.
In the figure below a scanning electron micrograph of a Nb/InN-nanowire/Nb junction is shown. The superconducting Nb electrodes are defined by electron beam lithography and magnetron sputtering.
A typical current voltage characteristics of a Nb/InN-nanowire/Nb junction is depicted in the figure below. At temperatures of 0.8 K a critical current, i.e. the maximum supercurrent, of more than 5 µA is observed. With increasing temperatures the critical current decreasing. The hysteresis in the current voltage characteristics can be attributed to heating effects.
R. Frielinghaus, I. E. Batov, M. Weides, H. Kohlstedt, R. Calarco, and Th. Schäpers,
Josephson supercurrent in Nb/InN-nanowire/Nb junctions
Appl. Phys. Lett. 96, 132504 (2010).
H. Y. Günel, I. E. Batov, H. Hardtdegen, K. Sladek, A. Winden, K. Weis, G. Panaitov, D. Grützmacher, and Th. Schäpers
Supercurrent in Nb/InAs-nanowire/Nb Josephson junctions
J. Appl. Phys. 112, 034316 (2012).