Supercurrent and Magnetoresistance Oscillations inNb/InAs-Nanowire/Nb Josephson junctions

One of the common goals in semiconductor/superconductor hybrid de-vices is to fabricate Schottky barrier free contacts at the interface of the two materials.[1] The natural formation of an electron accumu-lation layer on InAs surfaces prohibits the formation of a Schottky barrier. Therefore this material became the most preferred one for semiconducting weak links in Josephson junctions. This unique prop-erty of InAs in combination with the bottom-up growth approach of nanowires, led to many interesting experiments, e.g. tunable super-currents or Cooper pair beam splitters.[3] In these experiments aluminum (Al) was used as a superconducting material, which has a low critical temperature (Tc) and a low critical magnetic eld (Bc). As an alternative, we have used superconduct-ing Niobium (Nb) with a high Tc and Bc that oers the advantage to study Josephson properties in dierent regimes. In this report, we have used InAs nanowires with two dierent bulk carrier concentra-tions, i.e. 10 18 cm 3 (low doped) and 10 19 cm 3 (highly doped). The contacting process of Nb electrodes has been realized by standard electron beam lithography. We systematically investigated the basic Josephson properties, i.e. the eect of temperature, magnetic eld and electric eld on the super-current through InAs nanowires. By taking advantage of the high Tc ( 9:3K) of the superconducting Nb, we were able to measure a super-current up to 4.0K. The highest critical current Ic 100nA has been measured at 0.4K for a junctions with a highly doped InAs nanowire. For low doped nanowire Josephson junctions, a full control of the su-percurrent has been achieved by applying a gate bias. We have found a monotonous dependence of the measured critical current in the pres-ence of a perpendicular magnetic eld rather than a Fraunhofer-like diraction pattern. The experimental results have been compared to a recent theoretical model of Ref.[4] In addition, we studied the supercur-rent and conductance uctuations as a function of gate voltage. Here, a remarkable enhancement of the conductance uctuation amplitude has been observed. In the last part, we have studied the magnetore-sistance oscillations in the voltage state of Josephson junctions. [1] Th. Schapers, Superconductor/Semiconductor Junctions, 174 (Springer Tracts on Modern Physics, 2001) [2] Y.-J. Doh, J. A. van Dam, A. L. Roest, E. P. A. M. Bakkers, L. P. Kouwenhoven, and S. D. Franceschi, Science 309, 272 (2005) [3] L. Hofstetter, S. Csonka, J. Nygard, and C. Schonenberger, Na-ture 461, 960 (2009) [4] J. C. Cuevas and F. S. Bergeret, Phys. Rev. Lett. 99, 217002 (2007