  In condensed-matter systems, competition between ground states at phase
boundaries can lead to significant changes in material properties under
external stimuli, particularly when these ground states have different crystal
symmetries. A key scientific and technological challenge is to stabilize and
control coexistence of symmetry-distinct phases with external stimuli. Using
BiFeO3 (BFO) layers confined between layers of the dielectric TbScO3 as a model
system, we stabilize the mixed-phase coexistence of centrosymmetric and
non-centrosymmetric BFO phases with antipolar, insulating and polar,
semiconducting behavior, respectively at room temperature. Application of
in-plane electric (polar) fields can both remove and introduce centrosymmetry
from the system resulting in reversible, nonvolatile interconversion between
the two phases. This interconversion between the centrosymmetric insulating and
non-centrosymmetric semiconducting phases coincides with simultaneous changes
in the non-linear optical response of over three orders of magnitude, a change
in resistivity of over five orders of magnitude, and a change in the polar
order. Our work establishes a materials platform allowing for novel
cross-functional devices which take advantage of changes in optical,
electrical, and ferroic responses.
