Healing Effect of Controlled Anti-Electromigration on Conventional and High-Tc Superconducting Nanowires

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. As
demonstrated here, a combination of electromigration and anti-electromigration 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 (La 2−x Ce x CuO 4 ), the electromigration process acts selectively on
the oxygen atoms with no apparent modification of the structure. This allows to adjust
the doping of this compound and switch from a superconducting to an insulating
state in a nearly reversible fashion. In addition, the conditions needed to replace
feedback controlled electromigration by a simpler technique of electropulsing are
discussed. 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 for a reversible control of local properties of nanowires.