Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution

TL;DR

This study uses advanced electron microscopy to directly measure atomic displacements and charge transfer at the LAO/STO interface, providing strong evidence for intrinsic electronic reconstruction as the origin of the 2D electron gas.

Contribution

It presents the first direct atomic-scale measurements confirming electronic reconstruction as the cause of conductivity at the LAO/STO interface.

Findings

Atomic displacements correlate with charge transfer.

Evidence supports intrinsic electronic reconstruction over defect-based models.

Measurements reveal the origin of the 2D electron gas.

Abstract

The discovery that the interface between two band gap insulators LaAlO3 and SrTiO3 is highly conducting has raised an enormous interest in the field of oxide electronics. The LAlO3/SrTiO3 interface can be tuned using an electric field and switched from a superconducting to an insulating state. Conducting paths in an insulating background can be written applying a voltage with the tip of an atomic force microscope, creating great promise for the development of a new generation of nanoscale electronic devices. However, the mechanism for interface conductivity in LaAlO3/SrTiO3 has remained elusive. The theoretical explanation based on an intrinsic charge transfer (electronic reconstruction) has been strongly challenged by alternative descriptions based on point defects. In this work, thanks to modern aberration-corrected electron probes with atomic-scale spatial resolution, interfacial charge and atomic displacements originating the electric field within the system can be simultaneously measured, yielding unprecedented experimental evidence in favor of an intrinsic electronic reconstruction.