Multi-Terminal Superconducting Nonequilibrium Device With a Ferromagnetic Screen

We have fabricated and characterized double-barrier multi-terminal superconducting transistor-like devices with the Nb/Al/AlO_x/Al/Nb/Ni/Al/AlO_x/Al/Nb (S₁IS₂FIS₃) structure, where S, I, and F refer to superconducting, insulating, and ferromagnetic layers, respectively. A thin ferromagnetic Ni layer screens the superconductivity of the middle Nb layer on the injector-barrier side, so that the Nb/Ni bilayer manifests itself as a superconductor in the current-voltage characteristic (I-V curve) of the acceptor S₁IS₂ junction, but as a normal metal in the I-V curve of the injector S₂FIS₃ junction. It is shown that this property allows for considerable improvement of the input-output isolation of the quasiparticle-injection devices as compared with that for the formerly reported quiteron.