Controlling Ferroic Domain Architecture in Oxide Heterostructures

Abstract

The strong interplay between structural, electronic and chemical properties renders oxide materials very appealing in the hunt for novel technological designs. Outstanding examples include phenomena like colossal magnetoresistance and the appearance of a two-dimensional electron system (2DES) at the interface between two band insulators. Ferroic materials attract even more attention because they have a remanent state, i.e. a domain state, that is controllable with an external field. Different technological applications, for example the use in nonvolatile random-access memories for data storage, require specific domain states. As a result, the area of domain engineering in ferroic thin films is in continuous expansion and high structural quality is a persistent requirement. The advances in growth technology of ferroic oxide layers, approaching the same atomic precision attained in semiconductor heterostructures, are promoted by the employment of techniques that can monitor the structural development of the oxide while it is growing. The information about the structure, however, does not reveal the domain architecture. Nonlinear optical phenomena, and in particular second harmonic generation (SHG), possess the innate capability of detecting ordering phenomena, but their implementation to characterize single- and multi-layer ferroic systems is only at the early stages. In this work, SHG is utilized to discriminate the effects that strain, external fields and interfaces have on the film domain architecture at the nanoscale, beyond resolution limit. First, a correlation between the local distribution of the polarization, the symmetry of the compound and the nonlinear optical response is found. Then, the probing laser is coupled inside the growing chamber with the purpose of detecting in real time the emergence of the ferroelectric order. This paves the way for a complete comprehension of the mechanisms behind the development of the ferroic properties and might therefore assist the quest of integrating these complex materials into next-generation electronic devices.