Theory of the SrTiO3 Surface State Two-Dimensional Electron Gas

TL;DR

This paper develops a theoretical model for the surface 2DEG in SrTiO3, highlighting the importance of non-linear screening and predicting the coexistence of bulk-like and tightly bound surface bands at high carrier densities.

Contribution

It introduces a comprehensive theory accounting for non-linear and non-local screening effects in SrTiO3 surface 2DEGs, predicting the coexistence of different electronic bands.

Findings

Weakly bound bulk-like bands extend over many layers.

Tightly bound surface bands emerge at high carrier densities.

Non-linear screening is crucial for 2DEG properties.

Abstract

We present a theory of the quasi two-dimensional electron gas (2DEG) systems which appear near the surface of SrTiO$_3$ when a large external electric field attracts carriers to the surface. We find that non-linear and non-local screening by the strongly polarizable SrTiO$_3$ lattice plays an essential role in determining 2DEG properties. The electronic structure always includes weakly bound bulk-like bands that extend over many SrTiO$_3$ layers. At 2D carrier-densities exceeding $\sim 10^{14} {\rm cm}^{-2}$ tightly bound bands emerge that are confined within a few layers of the surface.