  The disposition of defects in metal oxides is a key attribute exploited for
applications from fuel cells and catalysts to superconducting devices and
memristors. The most typical defects are mobile excess oxygens and oxygen
vacancies, and can be manipulated by a variety of thermal protocols as well as
optical and dc electric fields. Here we report the X-ray writing of
high-qualitysuperconducting regions, derived from defect ordering, in the
superoxygenated layered cuprate, La2CuO4+y. Irradiation of a poor
superconductor prepared by rapid thermal quenching results first in growth of
ordered regions, with an enhancement of superconductivity becoming visible only
after a waiting time, as is characteristic of other systems such as
ferroelectrics, where strain must be accommodated for order to become extended.
However, in La2CuO4+y, we are able to resolve all aspects of the growth of
(oxygen) intercalant order, including an extraordinary excursion from low to
high and back to low anisotropy of the ordered regions. We can also clearly
associate the onset of high quality superconductivity with defect ordering in
two dimensions. Additional experiments with small beams demonstrate a
photoresist-free, single-step strategy for writing functional materials.
