Lead author Giordano Mattoni, PhD-student at TU Delft, says: ‘Our findings are a strong proof of the rising importance of complex oxides, which could be used in the electronics of the future. A fundamental milestone in the use of these materials in electronics was reached in 2004, when the formation of a two-dimensional electron system (2DES) was discovered at the interface between the insulators LaAlO3 (LAO) and SrTiO₃ (STO).’

Complex oxide materials offer many characteristics that cannot be achieved with current electronics, that is based on silicon. Superconductivity, ferro-electricity and magnetism are just a few of the many interesting phenomena that are observed in complex oxides. While the road towards industrial use of these material is still long, the work of the TU Delft researchers is significant proof of the potential held by oxide interfaces.

Interfaces between complex oxides constitute a unique playground for two-dimensional electron systems (2DES), where superconductivity and magnetism can arise from combinations of insulators. The formation of a two-dimensional electron system at the interface between the insulators STO and LAO is among the most intriguing and most studied effects in oxide electronics. The conductive layer that forms has a strongly two-dimensional character (it is a plane of electrons, about 10 nanometer in thickness), and presents a very high electron mobility and a strong magnetoresistance.

The origin of this 2DES is a long-standing question, and recent results indicate that the control of point defect formation is crucial to the realisation of high-quality electron systems. ‘A promising material to enhance the properties of the electron system at LAO/STO interfaces, is the metal oxide WO₃’, says Mattoni. ‘This material can host vacancies and interstitial atoms, which is why it is often utilized in electrochemical applications and electrochromic devices. In this work we demonstrated, for the first time, how WO₃ overlayers can effectively control the profile of defects, inducing a high mobility 2DES at WO₃/LAO/STO heterostructures’.

The experimental findings underscored WO₃ as a very efficient dopant for oxide interfaces. Starting from the results described in their paper, the researchers believe that WO₃ overlayers will be used to engineer novel conductive electron systems in other oxide materials. The work is thus an important step forward towards the rise of future complex oxide electronics.

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers, Giordano Mattoni, David J. Baek, Nicola Manca, Nils Verhagen, Dirk J. Groenendijk, Lena F. Kourkoutis, Alessio Filippetti , and Andrea D. Caviglia.
DOI: 10.1021/acsami.7b13202