Superconducting Spintronics

This programme will study the synergy between superconductivity and magnetism which can be engineered in certain devices and use this to demonstrate superconducting spintronics as future computing technology.

In ferromagnetic metals, an internal exchange field generates an imbalance in the number of electrons with up and down spins which means that currents that emerge from ferromagnets into non-magnetic metals carry a net spin in addition to charge. Such spin polarized currents are utilized for logic and sensor applications (for example in hard disk drives), and finding ways to generate and control them is a major goal of spin electronics (spintronics). However, the heat loss from the charge currents used to generate spin currents can be considerable and this is one reason why applications of spintronics, such as integrated memory chips, are presently limited.

In superconductors charge can flow without dissipation but, since the Cooper pairs consist of electrons with antiparallel spins, charge currents cannot carry spin. Further, since Cooper pairs are easily disrupted by magnetism, the coupling of superconductivity and ferromagnetism might appear useless for applications in spintronics. However, during the past few years a series of discoveries have shown that, not only can magnetism and superconductivity be made to cooperate, but in carefully engineered superconductor/magnet systems new functionality can be created in which spin, charge and superconducting phase coherence can work together. By combining these different degrees of freedom a whole new spectrum of recent predictions is waiting to be explored experimentally.
Through this ambitious programme we have the chance to transform this array of predictions and discoveries about the interaction between superconductivity and magnetism into a demonstration technology which could eventually be developed as a replacement for large-scale semiconductor-based logic. Our ideas for the proposed field of superconducting spintronics go far beyond the simple ideas of eliminating resistive losses inherent in conventional spin electronic (spintronic) circuits, but instead aim to exploit unique attributes of the superconducting state to control spin currents and spin accumulation.

The programme brings together teams from three different specialties - superconducting devices, high speed spintronics and theory of strong correlations in mesoscopic physics - which will work together to identify and investigate the key underpinning science. This basic science which will emerge from the programme will allow us to understand which of the many predicted effects are viable for long-term development.

The flexibility of a Programme Grant will allow us to work in parallel on all the potential elements and then progressively focus on those that show most promise for demonstrator devices: firstly a memory device which can store data indefinitely but can be switched with ultra-low energy and, secondly, some form of logic device. The latter may be a transistor-like structure or one of the all-spin logic devices proposed for conventional spintronics. The ambition for these superconducting spintronic devices is that they will combine the scalability inherent in conventional spintronics and the high speed and low power offered by superconductors. The risks are such that we may not be able to realise all of these ideas but, by working in parallel on a wide range of different phenomena which couple superconductivity and spin transport, we have a unique opportunity to define a new technology field.

The programme will focus on fundamental research which combines unconventional superconductivity and magnetism. The primary impact of the research will be greatly improved understanding of the behaviour of spin within hybrid magnetic / superconducting systems. Although this is itself a very active field within the UK and internationally, many aspects of these results are expected to extend beyond the immediate subject area to include fields such as quantum technology, unconventional superconductivity, and more general exotic states in condensed matter systems. In the longer term, we expect that the outputs of our research will form the foundation for a new technology - superconducting spintronics - for memory and logic devices that can operate with minimal Joule heating. While in present devices logic information is encoded using transistors as control switches between two different states, in the new devices information will be encoded via electron spin orientation, using input and output elements that are totally different from field-effect transistors. The resulting redesign will open up new avenues for investigation through evolutionary change and discontinuous revolutionary hardware architecture.