Discovering the secrets of oxide electronics
The fate of Fröhlich polarons in SrTiO3
Strontium titanate (SrTiO3) has been very well studied over the last decade, and we can easily measure many of its unusual properties such as superconductivity at very low carrier density. But until now we have lacked an understanding of what gives rise to this material’s special properties. A team of researchers using Diamond’s Angle-Resolved Photoemission Spectroscopy beamline (I05) to observe the behaviour of the electrons in this complicated material, have demonstrated that it depends strongly on carrier density. The results published in Nature Materials will help develop our theoretical understanding of oxide materials.
A great deal of research is being carried out in the field of oxide electronics, investigating this virtually unlimited source of materials with exotic properties, motivated partly by the search for a replacement for silicon as we approach the limits of what we can do with the current generation of electronics. Although we can easily measure the properties of these materials, their high-quality production is a challenge for materials science, and developing models to explain their properties is challenging for theoreticians. Observing electron-phonon interactions, thought to be the underlying cause for superconductivity in most materials, is a very important area of research for condensed matter physics.
Professor Felix Baumberger from the University of Geneva’s Department of Quantum Matter Physics, and the Spectorscopy of Novel Materials Group at the Paul Scherrer Institute.
SrTiO3 is widely used as a substrate for growing oxide films, but is a highly fascinating material in its own right. A band insulator, it becomes a superconductor when doped with less than 1 excess electron per 104 Ti ions, implying an exceptionally strong attractive interaction among diluted carriers. In combination with other materials, it plays a crucial role in creating novel physical properties, for example superconductivity above the temperature of liquid nitrogen in a single monolayer of FeSe grown on a SrTiO3 base. This critical temperature is higher than in any iron-based bulk material, suggesting a key role for the SrTiO3 substrate.
The Fröhlich polaron
Wang et al. Tailoring the nature and strength of electron–phonon interactions in the SrTiO3(001) 2D electron liquid. Nature Materials (2016). DOI: 10.1038/NMAT4623