ARPES Studies of Two-Dimensional Electron Gases at Transition Metal Oxide Surfaces

TL;DR

This paper reviews the development and understanding of two-dimensional electron gases at transition metal oxide surfaces, highlighting their electronic structure, surface preparation effects, and many-body interactions relevant for oxide electronics.

Contribution

It provides a systematic analysis of ARPES studies on surface 2DEGs in transition metal oxides, revealing their subband structure and interaction effects, advancing the field of oxide electronics.

Findings

Subband structures from quantum confinement are characterized.

Surface preparation influences 2DEG carrier densities.

Signatures of strong many-body interactions are observed.

Abstract

High mobility two-dimensional electron gases (2DEGs) underpin today's silicon based devices and are of fundamental importance for the emerging field of oxide electronics. Such 2DEGs are usually created by engineering band offsets and charge transfer at heterointerfaces. However, in 2011 it was shown that highly itinerant 2DEGs can also be induced at bare surfaces of different transition metal oxides where they are far more accessible to high resolution angle resolved photoemission (ARPES) experiments. Here we review work from this nascent field which has led to a systematic understanding of the subband structure arising from quantum confinement of highly anisotropic transition metal d-states along different crystallographic directions. We further discuss the role of different surface preparations and the origin of surface 2DEGs, the understanding of which has permitted control over 2DEG carrier densities. Finally, we discuss signatures of strong many-body interactions and how spectroscopic data from surface 2DEGs may be related to the transport properties of interface 2DEGs in the same host materials.