Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions

We demonstrate proximity-based all-metallic mesoscopic superconductor-normal metal-superconductor (SNS) field-effect controlled Josephson transistors (SNS-FETs) and show their full characterization from the critical temperature T_c down to 50 mK in the presence of both electric and magnetic fields. The ability of a static electric field-applied by means of a lateral gate electrode-to suppress the critical current I_s in a proximity-induced superconductor is proven for both positive and negative gate voltage values. I_s reached typically about one-third of its initial value, saturating at high gate voltages. The transconductance of our SNS-FETs obtains values as high as 100 nA/V at 100 mK. On the fundamental physics side, our results suggest that the mechanism at the basis of the observed phenomenon is quite general and does not rely on the existence of a true pairing potential, but rather the presence of superconducting correlations is enough for the effect to occur. On the technological side, our findings widen the family of materials available for the implementation of all-metallic field-effect transistors to synthetic proximity-induced superconductors.