Domains and Electrostatic Coupling in Ferroelectric Superlattices

Superlattices composed of ferroelectric and paraelectric oxides have been the subject of numerous studies, delving into fundamental questions about ferroelectric size effects, revealing novel interfacial phenomena, and opening new possibilities for tailoring the functional properties of these artificially layered ferroelectrics. Here we examine the role of periodic 180 degree ferroelectric nanodomains on the structural and electrical properties of PbTiO$_3$/SrTiO$_3$ superlattices. Using a combination of X-ray diffraction and electrical measurements, nanoscale motion of domain walls under applied field has been detected and linked to the large enhancement of the dielectric response. Electrostatic interactions between the ferroelectric layers have been studied in detail, revealing an unexpected decoupling of the ferroelectric layers once the paraelectric layer thickness exceeds just a few perovskite unit cells. Recent advances in transmission electron microscopy allowed us to map out the local structural distortions across the superlattice using electron energy loss spectroscopy with unit-cell resolution, revealing highly inhomogeneous polarization profiles near the interfaces and giving new microscopic insight into the behavior of these fascinating materials.