When working on the scale of a nanometre, superconductivity can be spread to a non-superconducting conductor, a “normal” conductor. This is called proximity superconductivity, as if superconductivity was contagious and could spread to its neighbours.
Indeed, superconductivity can go through insulators (if they are thin enough) by tunnel effect, and even spread to non-superconducting metals or magnetic metals. Superconductivity can go through a unique atom, a magnetic molecule, a nanotube or through graphene (carbon layer of one-atom width), and can appear quite unexpectedly at the interface of two insulating layers.
In the middle, we can see a bridge of gold, between two thicker superconductors (niobium). Below 4 K, the whole resistance drops to zero, which means the electron pairs cross this bridge made in a non-superconducting metal with no resistance! The gold wire is one-micrometre long (a millionth of a millimetre), a 70-nanometre length and a 200-nanometre breadth.
Crédits : Physique Mesoscopique, LPS, Orsay
Graphene surface sprinkled with indium superconducting nanoparticles (size: a few nanometres), to make it superconducting on its entire surface. In the absence of these nanoparticles, graphene is not superconducting. With them, it becomes superconducting on its entire surface.
