  The nanodomain pattern in ferroelectric/dielectric superlattices transforms
to a uniform polarization state under above-bandgap optical excitation. X-ray
scattering reveals a disappearance of domain diffuse scattering and an
expansion of the lattice. The reappearance of the domain pattern occurs over a
period of seconds at room temperature, suggesting a transformation mechanism in
which charge carriers in long-lived trap states screen the depolarization
field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter
and a critical carrier concentration for the transformation.
