Localized vs. delocalized character of charge carriers in LaAlO3/ SrTiO3 superlattices

TL;DR

This study uses resonant inelastic X-ray scattering to distinguish between localized and delocalized charge carriers in LaAlO3/SrTiO3 superlattices, clarifying discrepancies in carrier density measurements.

Contribution

It demonstrates a direct method to identify carrier types in oxide heterostructures and explains the origin of different carrier behaviors.

Findings

Presence of both localized and delocalized Ti 3d carriers.

Oxygen vacancies cause localized carriers.

Electron transfer at the interface causes delocalized carriers.

Abstract

Understanding the nature of electrical conductivity, superconductivity and magnetism between layers of oxides is of immense importance for the design of electronic devices employing oxide heterostructures. We demonstrate that resonant inelastic X-ray scattering can be applied to directly probe the carriers in oxide heterostructures. Our investigation on epitaxially grown LaAlO3/SrTiO3 superlattices unambiguously reveals the presence of both localized and delocalized Ti 3d carriers. These two types of carriers are caused by oxygen vacancies and electron transfer due to the polar discontinuity at the interface. This result allows explaining the reported discrepancy between theoretically calculated and experimentally measured carrier density values in LaAlO3/SrTiO3 heterostructures.