Direct k-space mapping of the electronic structure in an oxide-oxide interface

TL;DR

This study directly maps the electronic states at the LaAlO3/SrTiO3 interface using soft x-ray ARPES, revealing a charge dichotomy between mobile and localized electrons, and providing insights into the electronic reconstruction mechanism.

Contribution

It presents the first direct k-space mapping of interface states in an oxide-oxide heterostructure, elucidating the nature of electron confinement and localization.

Findings

Identification of Fermi surface sheets from mobile electrons.

Detection of localized electrons possibly trapped by oxygen vacancies.

Support for the electronic reconstruction model involving surface O-vacancies.

Abstract

The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O-vacancies in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be excluded, the apparent absence of surface-related Fermi surface sheets could also be fully reconciled in a recently proposed electronic reconstruction picture where the built-in potential in the LaAlO3 is compensated by surface O-vacancies serving also as charge reservoir.