Stabilization of Monodomain Polarization in UltrathinPbTiO3Films

Using in situ high-resolution synchrotron x-ray scattering, the Curie temperature $T_C$ has been determined for ultrathin $c$-axis epitaxial ${\mathrm{PbTiO}}_3$ films on conducting substrates (${\mathrm{SrRuO}}_3$ on ${\mathrm{SrTiO}}_3$), with surfaces exposed to a controlled vapor environment. The suppression of $T_C$ was relatively small, even for the thinnest film (1.2 nm). We observe that 180° stripe domains do not form, indicating that the depolarizing field is compensated by free charge at both interfaces. This is confirmed by ab initio calculations that find polar ground states in the presence of ionic adsorbates.