Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopy

TL;DR

This study uncovers how localized oxygen vacancies at the spinel/perovskite interface create a high-mobility two-dimensional electron system by reducing scattering, with implications for defect engineering in oxide interfaces.

Contribution

It reveals the microscopic origin of enhanced electron mobility at the heterointerface through combined spectroscopy and ab initio calculations, highlighting the role of localized oxygen vacancies.

Findings

Localized oxygen vacancies are present at the interface.

High mobility results from reduced scattering due to vacancy separation.

Spatial separation of the 2DES enhances mobility.

Abstract

The spinel/perovskite heterointerface $\gamma$-Al$_2$O$_3$/SrTiO$_3$ hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart LaAlO$_3$/SrTiO$_3$ by more than an order of magnitude despite the abundance of oxygen vacancies which act as electron donors as well as scattering sites. By means of resonant soft x-ray photoemission spectroscopy and \textit{ab initio} calculations we reveal the presence of a sharply localized type of oxygen vacancies at the very interface due to the local breaking of the perovskite symmetry. We explain the extraordinarily high mobilities by reduced scattering resulting from the preferential formation of interfacial oxygen vacancies and spatial separation of the resulting 2DES in deeper SrTiO$_3$ layers. Our findings comply with transport studies and pave the way towards defect engineering at interfaces of oxides with different crystal structures.