Magnetic inhomogeneity at a superconductor (S)-ferromagnet (F) interface converts spin-singlet Cooper pairs into spin-one triplet pairs. These pairs are immune to the pairbreaking exchange field in F and support a long-range proximity effect. Although recent experiments have confirmed the existence of spin-polarized triplet supercurrents in S-F-S Josephson junctions, reversible control of the supercurrent has been impossible because of the robust preconfigured nature of the inhomogeneity. Here, we use a barrier comprising three F layers whose relative magnetic orientation, and hence the interfacial inhomogeneity, can be controlled by small magnetic fields; we show that this enables full control of the triplet supercurrent and, by using finite element micromagnetic simulations, we can directly relate the experimental data to the theoretical models which provide a general framework to understand the role played by magnetic states in long-range supercurrent modulation.

The proximity coupling of a thin superconducting layer and an inhomogeneous ferromagnet can lead to a significant reduction of the critical temperature due to the generation of spin-polarized triplet Cooper pairs. We report critical temperature measurements of Co/Cu/NiFe(Py)/Cu/Nb superconducting pseudo spin valves (PSVs) in which the magnetization of the soft layer (Py) can be independently rotated in-plane with a magnetic field to create an angle (θ ) between it and the magnetization of Co. Here we observe results consistent with spin-triplet theory and demonstrate large changes in T C up to −120 mK as the Py layer is rotated from 0°(Co and Py are parallel) to 90°(Co and Py are orthogonal), which offers the potential for active control of the superconducting state. The key to this achievement is engineered magnetic anisotropy in Py, which enables well-defined control over the magnetization configuration of the PSV.

Whereas there exists considerable evidence for the conversion of singlet Cooper pairs into triplet Cooper pairs in the presence of inhomogeneous magnetic fields, recent theoretical proposals have suggested an alternative way to exert control over triplet generation:intrinsic spin-orbit coupling in a homogeneous ferromagnet coupled to a superconductor.Here, we proximity-couple Nb to an asymmetric Pt/Co/Pt trilayer, which acts as an effective spin-orbit coupled ferromagnet owing to structural inversion asymmetry. Unconventional modulation of the superconducting critical temperature as a function of in-plane and out-ofplane applied magnetic fields suggests the presence of triplets that can be controlled by the magnetic orientation of a single homogeneous ferromagnet. Our studies demonstrate for the first time an active role of spin-orbit coupling in controlling the triplets -an important step towards the realization of novel superconducting spintronic devices. arXiv:1709.03504v2 [cond-mat.supr-con] 24 Oct 2017 2 Conventional superconductivity arises from an attractive pairing of spin-up and spindown electrons, whereas ferromagnetism is due to an imbalance in the number of spin-up and spin-down electrons. In superconductor/ferromagnet (S/F) proximity structures, the competing nature of these two orders is the source of rich physics [1,2]. For example, two opposite spin-paired electrons of a Cooper pair enter different spin bands upon transmission into an adjacent F layer, resulting in a finite centre-of-mass momentum. This results in a weak oscillatory dependence of the superconducting transition temperature superimposed on the monotonic suppression due to increasing F layer thickness [3,4]. In more complex F/S/F trilayers, is higher when the F moments are antiparallel than parallel [1,[5][6][7], arising from the higher net pair-breaking exchange field in the parallel state.This spin-switch effect allows an active control of using magnetic states.In contrast, S/F'/F and F'/S/F systems have recently shown an enhancement in the proximity effect between the S and the F layers [8-11] for non-collinear F-moment alignments. This unusual proximity effect results from a conventional spin-zero singlet Cooper pair being transformed into a spin-one triplet Cooper pair. These long-ranged triplets (LRTs) consist of electrons from the same spin band, and are therefore immune to the pair-breaking exchange field in F, thereby enhancing the coupling between the twolayers. The increased coupling makes superconductivity spread across the whole system, which reduces by up to 120-400 mK [8,10,12]. Although the control of superconductivity by modulating magnetic states is attractive for applications in superconducting spintronics [13][14][15][16][17], precisely controlling the relative angle between the magnetic layers is difficult [8][9][10][17][18][19]. Practical applications require a simplified structure with fewer interfaces to minimize spin-scattering, motivating the exploration of alternative mechanisms for triplet generation.Theor...

Spin selectivity in a ferromagnet results from a difference in the density of up-and down-spin electrons at the Fermi energy as a consequence of which the scattering rates depend on the spin orientation of the electrons. This property is utilized in spintronics to control the flow of electrons by ferromagnets in a ferromagnet (F1)/normal metal (N)/ferromagnet (F2) spin valve, where F1 acts as the polarizer and F2 the analyser. The feasibility of superconducting spintronics depends on the spin sensitivity of ferromagnets to the spin of the equal spintriplet Cooper pairs, which arise in superconductor (S)-ferromagnet (F) heterostructures with magnetic inhomogeneity at the S-F interface. Here we report a critical temperature dependence on magnetic configuration in current-in-plane F-S-F spin valves with a holmium spin mixer at the S-F interface providing evidence of a spin selectivity of the ferromagnets to the spin of the triplet Cooper pairs.