Interface engineering of spin triplet Cooper pairs for spin-valve implementation

Abstract

Spin singlet Cooper pairs can be converted into equal-spin triplet pairs at a superconductor/heavy-metal interface under suitable conditions. Under current carrying conditions, these triplet correlations can give rise to a non equilibrium spin moment in the heavy metal through the predicted supercurrent spin-Hall effect. Here we demonstrate that this current induced triplet spin moment, in conjunction with the magnetic moment of a ferromagnetic layer, can enable a magnetic spin-valve response in Nb/Pt/Ni/Pt/Nb vertical nano-devices. The magnitude of this spin-valve effect depends on the efficiency of singlet-triplet Cooper pair conversion at the Nb/Pt interface. In order to facilitate efficient triplet generation, we deliberately introduced interfacial roughness to introduce finite Rashba spin-orbit coupling at the Nb/Pt interface and an out-of-plane component of magnetic moment at the Ni interface. In contrast, no discernible spin-valve response was observed in devices with smooth interfaces within measurement resolutions. Since the magnetic moment of the Ni layer and the current-induced triplet spin moment in the Pt layer are independently switchable using a magnetic field and bias current, respectively, the spin valve can be controlled via either parameters. These results demonstrates a novel approach to directly utilizing the spin polarized triplet Copper pairs in superconducting spintronic applications.