Spin is a particle’s inherent angular momentum and is usually carried in non-superconducting, non-magnetic materials by separate electrons. Spin can be ‘up’ or ‘down’, and for any particular material, there is a maximum length that spin can be carried. In a conventional superconductor electrons where opposite spins are paired together so that a flow of electrons carries zero spin.
Presently, the same team has discovered a set of materials that encourage the pairing of spin-aligned electrons, so that a spin current flows more efficiently in the superconducting state than in the non-superconducting (normal) state. Their results have been published in the Nature Materials journal.
Although some aspects of normal state spin electronics, or spintronics, are more efficient than standard semiconductor electronics, their large-scale application has been prevented because the large charge currents required to generate spin currents waste too much energy. A fully-superconducting method of generating and controlling spin currents offers a way to improve on this.
Professor Mark Blamire, Lead Researcher - Cambridge’s Department of Materials Science & Metallurgy
In the present work, Blamire and his collaborators used a multi-layered stack of metal films in which each layer was just a few nanometers thick. They noticed that when a microwave field was applied to the films, it caused the core magnetic layer to release a spin current into the superconductor next to it.
If we used only a superconductor, the spin current is blocked once the system is cooled below the temperature when it becomes a superconductor. The surprising result was that when we added a platinum layer to the superconductor, the spin current in the superconducting state was greater than in the normal state.
Professor Mark Blamire, Lead Researcher - Cambridge’s Department of Materials Science & Metallurgy
Although the team has demonstrated that specific superconductors can carry spin currents, so far these only take place across short distances. The subsequent step for the research team is to comprehend how to increase the distance and how to regulate the spin currents.
The study was financed by the Engineering and Physical Sciences Research Council (EPSRC).