The pairing state and critical temperature (T C ) of a thin s-wave superconductor (S) on two or more ferromagnets (F) are controllable through the magnetization-alignment of the F layers. Magnetization misalignment can lead to spin-polarized triplet pair creation, and since such triplets are compatible with spin-polarized materials they are able to pass deeply into the F layers and so, cause a decrease in T C . Various experiments on S/F 1 /F 2 "triplet spin-valves" have been performed with the most pronounced suppression of T C reported in devices containing the half-metal ferromagnet (HMF) CrO 2 (F 2 ) albeit using out-of-plane magnetic fields to tune magnetic noncollinearity [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Routine transfer of spin-polarized triplets to HMFs is a major goal for superconducting spintronics so as to maximize triplet-state spinpolarization. However, CrO 2 is chemically unstable and out-of-plane fields are undesirable for superconductivity. Here, we demonstrate low field (3.3 mT) magnetization-tuneable pair conversion and transfer of spin-polarized triplet pairs to the chemically stable mixed valence manganite La 2/3 Ca 1/3 MnO 3 in a pseudo spin-valve device using in-plane magnetic fields. The results match microscopic theory and offer full control over the pairing state.

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Materials with strongly correlated electrons often exhibit interesting physical properties. An example of these materials is the layered oxide perovskite Sr2RuO4, which has been intensively investigated due to its unusual properties. Whilst the debate on the symmetry of the superconducting state in Sr2RuO4 is still ongoing, a deeper understanding of the Sr2RuO4 normal state appears crucial as this is the background in which electron pairing occurs. Here, by using low-energy muon spin spectroscopy we discover the existence of surface magnetism in Sr2RuO4 in its normal state. We detect static weak dipolar fields yet manifesting at an onset temperature higher than 50 K. We ascribe this unconventional magnetism to orbital loop currents forming at the reconstructed Sr2RuO4 surface. Our observations set a reference for the discovery of the same magnetic phase in other materials and unveil an electronic ordering mechanism that can influence electron pairing with broken time reversal symmetry.

Spin-transport in superconductors is a subject of fundamental and technical importance with the potential for applications in superconducting-based cryogenic memory and logic. Research in this area is rapidly intensifying with recent discoveries establishing the field of superconducting spintronics. In this perspective, we provide an overview of the experimental state-of-the-art with a particular focus on local and nonlocal spin-transport in superconductors and propose device schemes to demonstrate the viability of superconducting spin-based devices.