Screening mechanisms at polar oxide heterointerfaces

Abstract

The interfaces of polar oxide heterostructures can display electronic properties unique from the oxides they border, as they require screening from either internal or external sources of charge. The screening mechanism depends on a variety of factors, including the band structure at the interface, the presence of point defects or adsorbates, whether or not the oxide is ferroelectric, and whether or not an external field is applied. In this review, we discuss both theoretical and experimental aspects of different screening mechanisms, giving special emphasis to ways in which the mechanism can be altered to provide novel or tunable functionalities. We begin with a theoretical introduction to the problem and highlight recent progress in understanding the impact of point defects on polar interfaces. Different case studies are then discussed, for both the high thickness regime, where interfaces must be screened and each interface can be considered separately, and the low thickness regime, where the degree and nature of screening can be manipulated and the interfaces are close enough to interact. We end with a brief outlook toward new developments in this rapidly progressing field.

Long-range Stripe Nanodomains in Epitaxial (110) BiFeO3 Thin Films on (100) NdGaO3 Substrate

“…The possible reason behind the different surface morphology between two thin film samples with and without LSCO interlayer can be explained in terms of different electrostatic and mechanical boundary conditions at the substrate/film interface. It should be noted that LSCO layer modifies the electrostatic boundary conditions at the bottom interface, where compensation of depolarizing fields by the screening charges could be critical to the stripe morphology in BFO/LSCO/NGO film 6,28 . In case of BFO/NGO heterostructures, the outer surface of the film will be compensated by free charges, since it is exposed to an ambient atmosphere 29 , while the interface between the BFO film and the NGO substrate will be isolated from the free charges as in the case reported for PbTiO 3 /SrTiO 3 heterostructures 30 .…”

“…In the case of ferroelectric thin films, the size and shape of the domains are determined by the energy competition between electrostatic, strain and domain wall energies. The two main factors that govern this energy competition are presence of screening charges and the thickness of the films 5,6 . In contrast, formation of the ferroelastic domains results from the balance of the elastic energy density against the domain wall energy 7–10 .…”

Designing functional ferroelectric interfaces from first-principles: dipoles and band bending at oxide heterojunctions

“…The band alignment scheme results as an effect of entangled microscopic mechanisms and plays a major role in setting the operating conditions of practical junctions [49,50]. Theory and computational methods, particularly those based on first principles calculations, have proven their usefulness in exploring the fundamental mechanisms at the interface with a ferroelectric, as well as by revealing practical routes for the device design based on predictive behavior; for a review in the field see [51].…”

Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures

“…The observation of emergent interfacial electronic reconstruction and, in turn, new electronic phases at polar-nonpolar oxide interfaces have launched numerous studies on the fundamental mechanisms for and potential uses of these exotic properties [1][2][3]. The nature of such electronic reconstruction (used here in the broad sense as any change in valence that results from the interfacial polar mismatch) depends on many factors such as the interfacial band alignment and the conductivity of the materials that can alter the boundary conditions and thus the degree of charge compensation [4]. To date, the most widely studied system in this regard is the two-dimensional electron gas in LaAlO 3 =SrTiO 3 [5].…”