Electronic structure and many-body effects in interfaces of oxide heterostructures

• Applicant: Professor Dr. Ralph Claessen
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2009 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 85460759

Transcending the capabilities of their conventional semiconductor counterparts, oxide interfaces provide the unique opportunity to control, enhance, and create functionalities such as superconductivity, magnetism, metal-insulator transitions, or topological phases. Striking examples are the correlated interface electron systems that form in the oxide heterostructures LaAlO3/SrTiO3 (LAO/STO) and LaVO3/SrTiO3 (LVO/STO) beyond a critical film thickness. This project is devoted to the fabrication of such hybrid systems by pulsed laser deposition and the study of their chemical and electronic interface structure by high-energy spectroscopies as well as scanning probe methods. Important questions to be addressed comprise the mapping of ferromagnetic and non-magnetic metallic patches at the LAO/STO interface using the contrast from x-ray magnetic circular dichroism in a scanning x-ray microscope and the in situ investigation of gating effects. Resonant techniques and cross-sectional scanning tunneling spectroscopy will be employed to directly probe the interface states, in particular the band-filling controlled Mott transition in LVO/STO. Another focus will be on the possibility to tune the dimensionality and hence the correlations of the two-dimensional electron system using vicinal substrates. Varying the LAO thickness and the STO miscut angle, a dimensional crossover has been predicted resulting in one-dimensional chains. We will systematically explore the relevant parameter space employing scanning tunneling microscopy and spectroscopy as well as angle-resolved photoelectron spectroscopy. This topic will be complemented by the investigation of reduced titanate nanowires which can be stabilized on bare STO surfaces. A last aspect concerns the creation of novel phases by design as has been highlighted lately for perovskite or perovskite-type high-Z metal oxide bilayers with (111)-orientation. In the presence of a large spin-orbit coupling topological insulators may result if the band topology is adjusted properly by applying an electric field or by sandwiching the bilayer between different substrates.

• DFG Programme: Research Units
• Subproject of: FOR 1162: Electron Correlation-Driven Phenomena in Surfaces and Interfaces with Tunable Interactions
• Participating Person: Professor Dr. Michael Sing