PNNL

Abstract

The ability to tailor oxide heterointerfaces on the atomic scale has led to novel properties in low-dimensional oxide systems not observed in the bulk. A fundamental understanding of these properties is based on the concept of electronic charge transfer. However, the electronic properties of oxide heterointerfaces crucially depend on their ionic constitution and defect structure: Ionic charges contribute to charge transfer and screening at oxide interfaces, triggering a thermodynamic balance of ionic and electronic structures. Quantitative understanding of the interplay of electronic and ionic roles in driving charge transfer phenomena is a central challenge in this field. Here we simultaneously investigate electronic and ionic structure at the prototypical charge-transfer-heterointerface, LaAlO3/SrTiO3. Applying in-situ photoemission spectroscopy under an oxygen ambient, we deconvolute ionic and electronic charge transfer across the buried interface in response to variable oxygen atmosphere at elevated temperatures. In this way, we embrace both the rich and variable chemistry of complex oxides and the associated electronic properties of nanoscale oxide heterointerfaces. The interfacial electron gas is depleted through an ionic rearrangement in the strontium cation sublattice when oxygen atmosphere is applied. The resulting ionic defects (Sr vacancies) and electrons show an inverse and reversible balance, indicated by their spectroscopic signatures. The mobility of ionic species in the vicinity of the interface is found to be considerably higher than in the bulk owing to the lower dimensionality, internal band bending and strong electric fields, resulting in fundamentally different ionic phenomena not accessible in the bulk. Triggered by enhanced ionic-electronic charge transfer, the electronic transport and magnetic signature of the heterointerface are significantly altered.