International network to explore novel superconductivity at advanced oxide superconductor/magnet interfaces and in nanodevices

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This International Network of world-leading experimental and theoretical groups in Japan, South Korea, Italy and the UK will lead a programme to explore novel superconductivity at oxide superconductor interfaces with magnetic materials and in nanodevices. Through a better understanding of materials properties and processing, our vision is to realise full control over superconducting symmetry at oxide interfaces and to setup Cambridge and Kyoto as a global hubs to explore the science of advanced oxide interfaces and unconventional superconductivity. The past decade has seen rapid developments in the understanding of unconventional superconductivity at the interface between conventional (s-wave) superconductors and ferromagnets [Nature Physics 11, 307 (2015)]. A highlight was the experimental demonstration of a triplet proximity effect by the UK applicants [Science 329, 59 (2010)], which required the transformation of spin-singlet Cooper pairs by a spin-mixing interface into spin-triplet pairs. Another example is a possible creation of electron-composite particle-antiparticles in nanowire/superconductor devices. Such Majorana Fermions are also expected in a half-quantum flux state of a spin-triplet superconductor, and the Japanese core member (Maeno) obtained the first evidence for this using superconducting micro-rings [Science 311, 186 (2011)]. In parallel, the understanding of unconventional superconductivity in superfluid helium and in compounds such as Sr2RuO4 (SRO) [e.g. Science 331, 186-188 (2011) and Science 344, 283 (2014)] has also seen dramatic advances. The triplet (p-wave) state in SRO is even-frequency and is conceptually different to the odd-frequency triplet pairing induced in ferromagnets on s-wave superconductors. However, there are theoretical predictions that alternative pairing states can be induced at surfaces, which raise the prospect of coupling different superconducting states via interface-engineered proximity effects between SRO and conventional superconductors. One of the key aims of the Network is to investigate the coupling of different superconducting symmetries taking SRO and ferromagnet/superconductor structures as a model system. There are theoretical predictions that the surface of SRO and ferromagnet/superconductor hybrids can support an induced odd-frequency triplet-state and so there should be a proximity effect from the conventional superconductor which would create or enhance the superconductivity in a SRO crystal or thin-film. Achieving this will enable detailed studies of the electron pairing state in SRO and the mixing of different superconducting order parameters, which have not previously been possible with single crystal samples.To bridge these novel superconducting states at oxide interfaces, further materials developments are critical. The global interest in unconventional superconductivity and recent high-impact realisations could lead to transformative science and simultaneously offer new paradigms of cryogenic computing and encryption. To lead this research, the Cambridge and Kyoto hubs will bring together different specialities including superconductivity, thin-film and crystal growth of oxides, materials characterization (XMCD, low energy muon spectroscopy, pump-probe terahertz spectroscopy, angle-resolved photoemission, electron microscopy), nanofabrication and theory. The members of the Network will work closely together with PhD students, PDRAs and investigators undertaking routine research visits between the member groups. As importantly the Network will actively engage with the wider scientific community through the organisation of conferences and student workshops, and research visits with the overarching aim of triggering a long-term global effort to lift basic science to application.