In situ tailoring of single superconducting junctions and nano-SQUIDs via current-induced atom migration

We demonstrate the in situ engineering of superconducting nanowires via modulation of material
properties through high applied current densities. We show that the sequential repetition of
such customized electro-annealing in a niobium nanoconstriction can broadly tune the superconducting
critical temperature Tc and the normal-state resistance Rn in the targeted area. Once a
sizable Rn is reached, clear magneto-resistance oscillations are detected along with a Fraunhoferlike
field dependence of the critical current, indicating the formation of a weak link with adjustable
characteristics. Applying this method to aluminum nanoconstrictions, it is possible to modify
their geometry and consequently their weak links’ properties beyond the limit of current lithography
techniques. Furthermore, conducting parallel electromigration in aluminum SQUIDs
allows us to investigate the evolution of the superconducting properties of the SQUID as function
of the cross section of the weak links and eventually access a regime where the SQUID can be
operated in the dissipative state. We will also discuss the possibility to change the local oxygen
doping in constrictions made of High-Tc materials.