Interfacial magnetism in topological insulator heterostructures

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Project description:About 5% of electricity is wasted during transmission, while electric appliances convert a large fraction of the electricity into unwanted heat. This project aims at investigating a new class of materials with the potential to overcome dissipation of energy. Three-dimensional topological insulators ("Tis") have an insulating bulk but conductive surfaces, which are topologically protected - a consequence of large spin-orbit coupling and time reversal symmetry. In magnetically doped TIs, the quantum anomalous Hall effect ("QAHE") was predicted and experimentally confirmed in 2013. Similar to the quantum Hall effect ("QHE"), which was observed several decades earlier, chiral, dissipationless transport takes place at the edges of the sample. The QHE is difficult to realise since high magnetic fields and low temperatures are required. The QAHE is much less demanding, being satisfied with the presence of certain magnetic and topological properties of the host materials. The challenge is to find suitable materials which have these properties at technically feasible temperatures, ideally at room temperature.The Project will aim to deliver ground-breaking experimental results on topological magnetic materials, in particular TIs proximity-coupled to AFs, using an integrated, synchrotron- and neutron-based multi-tool approach. It aims at achieving a big leap forward towards the realisation of the QAHE at high temperatures, which will put an end to the need for expensive cooling and external magnetic fields and will be ground-breaking for innovations in energy-efficient electronic devices. We will combine topological insulators with antiferromagnets (AFs) to induce magnetic order in the TIs and achieve a gap-opening in the band structure of the Dirac surface states - requirements for the QAHE and explore the potential for increasing the temperature beyond cryogenic temperatures. AFs benefit from many advantages compared to ferromagnets, such as a higher magnetic ordering temperature and a stronger proximity effect. Furthermore, no magnetic stray fields are produced due to the compensated spin structure of the AF, facilitating the magnetic characterisation of the TI and consequently supporting the optimisation of the materials.The significance of this Project is to expand the operation of the QAHE towards even higher temperatures by AF-TI proximity coupling. We envision to make use of the combined unique capabilities of Diamond and ISIS, and propose a multi-method study of the magnetic properties (XAS/XMCD/XMLD, XPEEM, PNR) and electronic properties (HAXPES, transport).This project is a joint project with the Diamond Light Source (Dr Dirk Backes) and ISIS/STFC (Prof Sean Langridge).This project aligns with EPSRC's research areas "Condensed Matter: Magnetism and Magnetic Materials" and "Spintronics".