Superconductivity in Bi-Ni multilayers
Neither Bi nor Ni are superconductors. Moreover, Ni is magnetic, which is at odds with superconductivity in general. However, Bi-on-Ni thin films do become superconducting at about 4K (Ref). Although there are several contradictory experiments reported in the literature, it seems that the formation of intermetallic compound Bi3Ni at the boundary between Bi and Ni is responsible for the effect, even in when Bi3Ni is in contact with magnetic Ni. This project tests the superconductivity in multilayer thin films of Bi and Ni and also ex-situ lithographic patterning and making superconducting (weak) links between films of different compositions.
Figure. The superconducting transition in Bi-Ni multilayers as a function of the temperature T (left) at zero magnetic field and the magnetic field (right) at T = 2 K. The labels refer to the top- and bottom multilayer films as well as their overlap (“cross’”).