Functional ferroic heterostructures with tunable integral symmetry

Abstract

The relation between symmetry and functionality was pinpointed by Pierre Curie who stated that it is the symmetry breaking that creates physical properties. This fundamental principle is nowadays used for engineering heterostructures whose integral symmetry leads to exotic phenomena such as one-way transparency. For switching devices, however, such symmetry-related functionalities cannot be used because the symmetry in conventional heterostructures is immutable once the material has been synthesized. Here we demonstrate a concept for post-growth symmetry control in PbZr 0.2 Ti 0.8 O 3 and BiFeO 3 -based heterostructures. A conducting oxide is sandwiched between two ferroelectric layers, and inversion symmetry is reversibly switched on or off by layer-selective electric-field poling. The generalization of our approach to other materials and symmetries is discussed. We thus establish ferroic trilayer structures as device components with reversibly tunable symmetry and demonstrate their use as light emitters that can be activated and deactivated by applying moderate electric voltages.

Probing Ferroelectric Domain Engineering in BiFeO3 Thin Films by Second Harmonic Generation

“…These lines are the result of destructive interference of SHG contributions emitted from oppositely polarized areas, here referring to the out‐of‐plane polarization component of the as‐grown and the poled region. As the sketch below Figure a shows, the opposite polarization is associated with a 180° phase difference of the corresponding SHG wave . Figure b shows an image of the same area as in (a), but taken with the SHG light produced by the surface of the BFO film.…”

Probing Ferroic States in Oxide Thin Films Using Optical Second Harmonic Generation

“…The manipulation of the polarization orientation during the growth in a multilayer will have an important role in future applications. In addition, artificial domain walls with arbitrary polarization sequences [120] offer a wide range of physical properties [11,114,120] and can for instance be designed on demand. A possible application would deal with the ability to electrically tune the symmetry environment of a layer sandwiched between two ferroelectric films [120].…”

“…In addition, artificial domain walls with arbitrary polarization sequences [120] offer a wide range of physical properties [11,114,120] and can for instance be designed on demand. A possible application would deal with the ability to electrically tune the symmetry environment of a layer sandwiched between two ferroelectric films [120]. The capacity to set and verify buried polar states during the growth [61] allows tuning of the strain, charge and symmetry environment of an adjacent active layer such as symmetry sensitive topological states, metal insulator transitions or colossal magnetoresistance systems.…”

“…Strikingly, a non-zero SHG intensity is observed at the edges of the tip-poled region which cannot be explained by the assumed Ising-like 180 • domain walls architecture in strained thin films [97,120]. At 180 • Ising-like domain walls, the contributions of SHG response from the neighboring opposite domains interfere destructively due to a 180 • phase difference [79,88].…”

“…The emergence of the ferroelectric polarization in BTO is shown in Figure 17d. The ability to probe multilayer systems [61,120] opens new avenues towards understanding the complex interplay between strain, interfaces, and electrostatics in oxide superlattices. Interfering signals originating from each polar constituent of a superlattice result in destructive or constructive interference depending on their relative polarization orientation.…”