The electromigration process has the potential capability to move atoms one by one when properly controlled. It is therefore an appealing tool to tune the cross section of monoatomic compounds with ultimate resolution or, in the case of polyatomic compounds, to change the stoichiometry with the same atomic precision. We demonstrate that a combination of electromigration and antielectromigration can be used to reversibly displace atoms with a high degree of control. This enables a fine adjustment of the superconducting properties of Al weak links, whereas in Nb the diffusion of atoms leads to a more irreversible process. In a superconductor with a complex unit cell (La2−xCexCuO4), the electromigration process acts selectively on the oxygen atoms with no apparent modification of the structure. This allows us to adjust the doping of this compound and switch from a superconducting behaviour to an insulating state in a nearly reversible fashion. We discuss the conditions needed to replace feedback controlled electromigration by a simpler technique of electropulsing. These findings have a direct practical application as a method to explore the dependence of the characteristic parameters on the exact oxygen content and pave the way towards a reversible control of local properties of nanowires.

We demonstrate the in situ engineering of superconducting nanocircuitry by targeted modulation of material properties through high applied current densities. We show that the sequential repetition of such customized electro-annealing in a niobium (Nb) nanoconstriction can broadly tune the superconducting critical temperature T and the normal-state resistance R in the targeted area. Once a sizable R is reached, clear magneto-resistance oscillations are detected along with a Fraunhofer-like field dependence of the critical current, indicating the formation of a weak link but with further adjustable characteristics. Advanced Ginzburg-Landau simulations fully corroborate this picture, employing the detailed parametrization from the electrical characterization and high resolution electron microscope images of the region within the constriction where the material has undergone amorphization by electro-annealing.

Weak link modification through current-induced atom displacement in order to tune the SQUID's response.