Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Correlated Electrons: Low-dimensional Systems - Materials 1

TT 22.2: Talk

Wednesday, March 28, 2012, 09:45–10:00, H 0104

Negative compressibility at LaAlO₃/SrTiO₃ interfaces explored with scanning force microscopy — •Veronika Tinkl¹, Martin Breitschaft¹, Christoph Richter^1,2, German Hammerl¹, Thilo Kopp¹, and Jochen Mannhart^1,2 — ¹Experimentalphysik VI, Zentrum für Elektronische Korrelationen und Magnetismus, Universität Augsburg, Augsburg — ²Max-Planck-Institut für Festkörperforschung, Stuttgart

The interface between the band insulators LaAlO₃ and SrTiO₃ is currently one of the most actively investigated structures in the field of oxide interfaces. If the LaAlO₃-film thickness exceeds three unit cells on a TiO₂-terminated SrTiO₃ substrate a conducting layer is formed at the interface. This conducting layer can be driven insulating by electric fields. In this presentation we will demonstrate that the interface exhibits negative compressibility as the carrier density is reduced.

We investigated interfaces consisting of four unit cells LaAlO₃ with a low temperature ultra-high vacuum scanning probe microscope. Contact potential difference measurements were performed at various carrier densities of the interface electron system. The difference in the work functions of interface and tip depends on the applied electric field. We will show that the chemical potential at the interface increases with decreasing carrier density. This effect is caused by electron-electron interactions and corresponds to a negative compressibility. The negative compressibility gives rise to applications by, for example, making use of the resulting large enhancement of the capacitance.
Lu Li et al., Science 332, 825 (2011).