Supercurrent manipulation in InSb nanoflag-based Josephson Junctions by Scanning Gate Microscopy

In this Master’s thesis work we report the first Scanning Gate Microscopy experiments on superconducting weak links, demonstrating the possibility of manipulating the supercurrent flow across a semiconductor-superconductor heterostructure through the charged tip of an atomic force microscope at a local level. To this end, we have employed a new generation of Nb-contacted ballistic InSb nanoflag-based Josephson junctions. We performed a full magneto-transport characterization of these devices at 300mK. Fully gate-tunable Josephson effect as well as larger switching currents with respect to the previous Nb/Ti contact design have been observed. Furthermore, we report evidence of fully developed Fraunhofer side lobes, as well as observation of Multiple Andreev Reflections, demonstrating the high transparency of the superconductor/semiconductor interfaces. Scanning Gate Microscopy measurements on superconducting junctions clearly show tip-induced modulation of critical current due to the local charge carrier depletion of the semiconducting region. Our experimental findings are consistent with theoretical simulations and establish a new way of investigating the behavior of superconducting weak links, with a view to supercurrent flow imaging and local investigation of topological samples.