Topological Spintronics

"Spin" is an intrinsic form of angular momentum universally carried by elementary particles, composite particles, and atomic nuclei. It is a solely quantum phenomenon and has no counterpart in classical mechanics. Many fundamental questions of the electrons' spin remain open issues up to this date: the spin-orbital coupling, spin-photon interaction, and spin wave transmission to name a few. Significantly, the discovery of giant magnetoresistance effect, celebrated by the 2007 Nobel Prize, has generated a revolutionary impact on the data storage technologies. This triggered the rise of Spintronics (or Spin-Electronics), an interdisciplinary subject dedicated for the study of spin-based other than or in addition to charge-only-based physical phenomena of electronic systems.

The recently discovered topological phase has presented new possibilities for spintronics: even the insulating state of matter exhibits a conductivity at the edges of certain physical systems and such conductive states are nontrivial and robust. Their unique spin-lock behaviours not only enrich the world of low-dimensional physics, but also provide a platform for transformative technical innovations. Traditionally spin phenomena have long been investigated within the context of ferromagnetic metals and alloys, the study of spin generation, relaxation, and spin-orbit coupling in non-magnetic materials took off only recently with the advent of hybrid spintronics and it is here many novel materials and architectures can find their greatest potentials in both science and technology. In the pursuit for such goals, the intrinsic material properties (e.g. mobility, anisotropy, conductivity etc.) are important indicators and the artificially synthesized hybrid systems (e.g. multilayers, hybrid systems, and nano-structures etc.) are valuable models for studying the topologically protected spin phenomena and could potentially be used as actual components for an eventual logic device.

This project focuses on the experimental studies (nano-fabrication and characterisation) of magnetic topological insulators. They are expected to give rise to Quantum Anomalous Hall effect and further coherent spin transport phenomena, in which Joule heating are minimised and therefore can be used in the next generation energy-efficient electronics. This will be assisted via proximity to a high-Curie-temperature ferromagnetic insulator to boost the spin ordering temperature of the selected systems.

The proposed project has an immediate impact on developing experimental approaches that can underpin the application of coherent spin phenomena, and understanding of the relevant scientific concepts. It directly addresses some of the grant challenges in Spintronics and Condensed Matter such as the demonstration of quantum anomalous Hall (QAH) effect and proximity effect with insulators. These capture state-of-the-art challenges across a range of fundamental questions related but not limited to topological spintronics.

There is a vision to advance, and to explore new materials, architectures and mechanisms to manipulate electrons spin transport, in which Joule heating and dissipation are minimised and therefore can be used in the next generation energy-efficient electronics. As such the proximity effect, as described in the proposal, offers tantalising possibilities of nontrivial phenomena that traditionally heavily rely on extreme physical conditions (high field and low temperature). This will not only provide opportunities to revolutionise the understanding of the fundamental science, but also a pathway to spintronic applications beyond cryogenic temperature.

Such energy-efficient electronics have been widely regarded as a 'general-purpose technology' - a technology that makes possible other important technologies, products and services, which will contribute greatly to economic growth and welfare. Today the semiconductor-based electronics industry is on the verge of entering uncharted territory for the first time in more than 50 years. By establishing UK as a leader in spintronics research, it will be at the forefront of a new wave of technological revolution, leading to significant international competitiveness. In this regard, this project will play the role of informing the society of the future trend, providing the relevant technical communities with the preliminary results, and providing information of the feasibility for mass productions.

Above can only happen in locations with a wide base of potential employees who are well versed in the relevant concepts, which are radically different to those involved in existing technologies. In this regard the project also has a primary impact in providing a strong stream of graduate and PhD students flowing from the university (the research group) into industry and commerce. The output of highly educated people rather than the research results themselves can be an even more effective knowledge transfer mechanism.