  Material surfaces encompass structural and chemical discontinuities that
often lead to the loss of the property of interest in the so-called dead
layers. It is notably problematic in nanoscale oxide electronics, where the
integration of strongly correlated materials into devices is obstructed by the
thickness threshold required for the emergence of their functionality. Here, we
report the stabilization of ultrathin out-of-plane ferroelectricity in oxide
heterostructures through the design of an artificial flux-closure architecture.
Inserting an in-plane polarized ferroelectric epitaxial buffer provides
continuity of polarization at the interface, and despite its insulating nature
we observe the emergence of polarization in our out-of-plane-polarized model
ferroelectric BaTiO$_{3}$ from the very first unit cell. In BiFeO$_{3}$, the
flux-closure approach stabilizes a conceptually novel 251$^{\circ}$ domain
wall. Its unusual chirality is likely associated with the ferroelectric analog
to the Dzyaloshinskii-Moriya interaction. We thus see that in an adaptively
engineered geometry, the depolarizing-field-screening properties of an
insulator can even surpass those of a metal and be a source of new
functionalities. This should be a useful insight on the road towards the next
generation of ferroelectric-based oxide electronics.
