Towards a controllable SQUID

Josephson junctions and superconducting quantum interference devices (SQUID) are important electronic elements, which are based on normal conductor sandwiched between two superconductors. These junctions are produced by evaporation techniques, and once they are embedded in an electronic circuit, their properties are fixed. Using SQUIDs as a tunable component requires the ability to generate Josephson junctions in situ in a reversible controllable manner. In this work we demonstrated how a normal (metallic) region along a line traversing a superconductor can be turned on and off externally thus potentially generating a controllable Josephson junction or a SQUID. The concept is based on a long, current-carrying excitation coil, piercing a ring shaped superconductor with nucleation points. The vector potential produced by this coil generates a circular current that destroys superconductivity along a radial line starting at the nucleation point. Unlike the destruction of superconductivity with magnetic field, the vector potential method is reversible and reproducible; full superconductivity is recovered upon removing the current from the coil and different cool-downs yield the same normal lines.