Research: Modelling Complex Oxide Heterostructures

Supervisors: Emilio Artacho (Earth Sciences) and Peter Littlewood (Cavendish)

The focus of my PhD is on an understanding of the atomic and electronic structure of oxide heterostructures using both ab initio simulations and analytical modelling. Current research is on structures with a polar component that requires charge screening. This screening can be in the form of free carriers and/or charged point defects.

Recent results include:

"Oxide superlatices with alternating p and n interfaces"

The transition from insulating to metallic interfaces with film thickness is predicted with first principles calculations in a pristine superlattice of LaAlO₃ and SrTiO₃. The calculations are supported by a simple electrostatic model which elucidates the origin of the interface electron gas as a screening of the polar interface.

Bristowe N C, Artacho E and Littlewood P B 2009 Phys. Rev. B 80 045425

"Surface defects and conduction in oxide heterostructures"

The origin of the two dimensional gas appearing at the interface between LaAlO₃ and SrTiO₃ is highly debated. Here we present a case for the origin, using a model supported with first principles calculations and experimental data, as surface redox reactions which transform surface bound charge to free-carrier charge, which is then able to move to the interface.

Bristowe N C, Littlewood P B and Artacho E 2011 Phys. Rev. B 83 205405

"The net charge at interfaces between insulators"

The issue of the net charge at insulating oxide interfaces is briefly reviewed with the ambition of dispelling myths of such charges being affected by covalency and related charge density effects.

Bristowe N C, Littlewood P B and Artacho E 2011 J. Phys.: Condens. Matter 23 081001

"Electrochemical ferroelectric switching"

The origin of polarization reversal in ultrathin ferroelectric films [Garcia et al., Nature 460, 81 (2009)] is proposed as electrochemical processes.

Bristowe N C, Stengel M, Littlewood P B, Pruneda J M and Artacho E 2011 Phys. Rev. B 85 024106

"1DEG in the steps at the LAO-STO interface"

A prediction of a one-dimensional electron gas residing in the steps at the LAO-STO interface is supported with first principles calculations and electrostatic modelling that elucidate the origin of the 1DEG as an electronic transfer to compensate a net charge at the step edge.

Bristowe N C, Fix T, Blamire M G, Littlewood P B and Artacho E 2011 arXiv:1111.6165