LaAlO3 stoichiometry found key to electron liquid formation at LaAlO3/SrTiO3 interfaces

TL;DR

This study reveals that the stoichiometry of LaAlO3, specifically Al-rich composition, is crucial for the formation of the electron liquid at LaAlO3/SrTiO3 interfaces, independent of extrinsic defects.

Contribution

It demonstrates that intrinsic LaAlO3 stoichiometry controls 2-DEL formation, challenging the focus on extrinsic defects in previous studies.

Findings

Al-rich LaAlO3 enables 2-DEL formation

Intrinsic electronic reconstruction occurs without extrinsic defects

Stoichiometry is key to emergent interface phenomena

Abstract

Emergent phenomena, including superconductivity and magnetism, found in the two-dimensional electron liquid (2-DEL) at the interface between the insulators LaAlO3 and SrTiO3 distinguish this rich system from conventional two-dimensional electron gases at compound semiconductor interfaces. The origin of this 2-DEL, however, is highly debated with focus on the role of defects in the SrTiO3 while the LaAlO3 has been assumed perfect. Our experiments and first principles calculations show that the cation stoichiometry of the nominal LaAlO3 layer is key to 2-DEL formation: only Al-rich LaAlO3 results in a 2-DEL. While extrinsic defects including oxygen deficiency are known to render LaAlO3/SrTiO3 samples conducting, our results show that in the absence of such extrinsic defects, an interface 2-DEL can form. Its origin is consistent with an intrinsic electronic reconstruction occurring to counteract a polarization catastrophe. This work provides a roadmap for identifying other interfaces where emergent behaviors await discovery.