  The sheet resistance Rs of Ar+ irradiated SrTiO3 in patterns with a length
scale of several microns increases significantly below 40 K in connection with
driving currents exceeding a certain threshold. The initial lower Rs is
recovered upon warming with accelerated recovery around 70 and 160 K. Scanning
superconducting quantum interference device microscopy shows local irreversible
changes in the spatial distribution of the current with a length scale of
several microns. We attribute the observed nonuniform enhancement of Rs to the
attraction of the charged single-oxygen and dioxygen vacancies by the
crystallographic domain boundaries in SrTiO3. The boundaries, which are nearly
ferroelectric below 40 K, are polarized by the local electrical field
associated with the driven current and the clustered vacancies which suppress
conductivity in their vicinity and yield a noticeable enhancement in the device
resistance when the current path width is on the order of the boundary
extension. The temperatures of accelerated conductivity recovery are associated
with the energy barriers for the diffusion of the two types of vacancies.
