Two-dimensional electron gas at the PbTiO$_3$/SrTiO$_3$ interface: an ab initio study

TL;DR

This study uses ab initio simulations to explore how ferroelectric polarization influences the formation and control of two-dimensional electron gases at PbTiO₃/SrTiO₃ interfaces, supporting the polar catastrophe model.

Contribution

It introduces ferroelectric thin films as a means to control 2DEG formation and demonstrates switchable charge states at the interface, advancing interface engineering techniques.

Findings

Ferroelectric layers stabilize in out-of-plane monodomain configuration due to free-carrier screening.

System can be switched between three stable polarization states, enabling non-volatile charge manipulation.

Results support the polar catastrophe model for 2DEG formation at oxide interfaces.

Abstract

In the polar catastrophe scenario, polar discontinuity accounts for the driving force of the formation of a two-dimensional electron gas (2DEG) at the interface between polar and non-polar insulators. In this paper, we substitute the usual, non-ferroelectric, polar material with a ferroelectric thin film and use the ferroelectric polarization as the source for polar discontinuity. We use ab initio simulations to systematically investigate the stability, formation and properties of the two-dimensional free-carrier gases formed in PbTiO$_3$/SrTiO$_3$ heterostructures under realistic mechanical and electrical boundary conditions. Above a critical thickness, the ferroelectric layers can be stabilized in the out-of-plane monodomain configuration due to the electrostatic screening provided by the free-carriers. Our simulations also predict that the system can be switched between three stable configurations (polarization up, down or zero), allowing the non-volatile manipulation of the free charge density and sign at the interface. Furthermore, the link between ferroelectric polarization and free charge density demonstrated by our analysis constitutes compelling support for the polar catastrophe model that is used to rationalize the formation of 2DEG at oxide interfaces.