Spin-Orbit Coupling-Driven Superconducting Spintronics

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Ferromagnetism arises from parallel alignment of electron spins in a material and is much stronger than conventional singlet superconductivity resulting from the pairing of electrons with opposite spins. Therefore, the coupling or the proximity effect between superconductivity and ferromagnetism is short-ranged and is restricted to only a few nanometres from the interface of the two materials.However, in the last ten years surprising results from the interaction of superconductivity and ferromagnetism has challenged this conventional picture. At suitably engineered superconductor/ferromagnet interfaces, it is possible to generate superconductivity mediated by equal spin-paired electrons (triplet pairs) enabling a superconductor to carry a dissipationless current with a non-zero spin. The finite spin-polarisation and the zero dissipation integrates the rich potentials of spin based electronics (spintronics) and superconducting electronics into a rich new field of superconducting spintronics. Although attractive both fundamentally and in its reach for potential applications, generating triplet pairs at superconductor/ferromagnet interfaces require prohibitively complex magnetic structures.Strikingly, a dramatic simplification can be achieved by incorporating spin-orbit coupling in superconductor/ferromagnet heterostructures. Our recent experiments have indicated that using heavy-metals at superconductor/ferromagnet interfaces, it is possible to generate and control triplet pairs using a simple homogeneous ferromagnet. This not only radically simplifies structures used in superconducting spintronics but opens-up the possibility to study a new class of effects predicted to occur due to the coexistence of superconductivity, ferromagnetism and spin-orbit coupling.In this proposal, we will establish our understanding by focusing on three key areas: understanding the role of the materials and interfaces, maximise the triplet generation efficiency and finally, demonstrate a functional device working on triplet generation and control using spin-orbit coupling. With these objectives, we hope to achieve i) spin-orbit coupling as an efficient source and controlling factor for triplets thereby making superconducting spintronics ideas practically feasible ii) a functional device that is far simpler than any previously designed and serves as a blue-print for future device designs with radically new functionalities.