Supercurrent and multiple Andreev reflections in Ge hut nanowire Josephson junctions

We report an experimental study of induced superconductivity in Ge hut nanowire Josephson junctions. The Ge hut nanowires are grown on prepatterned SiGe ridges via molecular beam epitaxy and Josephson junction devices are fabricated by contacting the nanowires with Al electrodes. Low-temperature current-bias transport measurements of the Josephson junctions are performed and the measurements show that the devices exhibit gate-tunable supercurrent and excess current. The analysis of excess current indicates that the transparency of the Ge hut nanowire Josephson junctions is as high as 85%. Voltage-bias spectroscopy measurements of the devices show multiple Andreev reflections up to the fourth order. With magnetic field and temperature-dependent measurements of the multiple Andreev reflections, the critical field and the critical temperature of the induced superconductivity in the Josephson junctions are extracted to be ∼0.12 T and ∼1.4 K. The success in introducing superconductivity into Ge hut nanowires will stimulate their applications in building advanced quantum processors.