Tuning superconductivity with spin–orbit coupling and proximity effects in ferromagnet/superconductor/ heavy metal heterostructures

Abstract

In superconducting/ferromagnet heterostructures, spin-triplet Cooper pairs that carry spin information are crucial for the realization of superconducting spintronics. It has been theoretically proposed that they can be generated and controlled by the magnetic proximity effect and spin orbit coupling (SOC), resulting in a change in the critical temperature (T C). However, experiments are still lacking, which limits the development of device applications. Here, we fabricate a series of Co/Nb/Pt heterostructures and reference samples, where the SOC and magnetic proximity can be independently controlled. We found the suppression of T C up to 11% by the different Rashba-SOC at the Nb/Pt and Nb/Cu interfaces, and the normalized T C/T C 0 was successfully tuned by 24% with the coeffect of SOC and magnetic proximity. Through rigorous comparison, we attribute the tuning of superconductivity to the spin-triplet Cooper pairs, which is controlled by both the SOC strength and magnetic proximity. Our results offer a new pathway to control superconductivity with SOC and pave a new direction for the design of superconducting spintronics devices.

Tunnel Josephson Junction with Spin–Orbit/Ferromagnetic Valve

“…The next promising direction in the development of superconducting spintronics is the use in spin valves of heavy metals or other materials in which spin–orbit interaction takes place either in themselves or at their boundaries with a superconductor or ferromagnet (see the review [ 49 ] and the references therein). In these devices, the critical temperature of the S-layer can be turned either by converting s-wave singlets into other types of correlations, among them s-wave odd-frequency pairs robust to impurity scattering [ 50 , 51 ], or by manipulating the direction or magnitude of the ferromagnetic moment acting on the S-layer [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ]. The implementation of SOI in the structures reveals the novel class of the spin valve devices that contain the only ferromagnetic layer.…”

“…The proposed device is a tunnel Josephson contact between a massive superconductor S and a multilayered sN F structure consisting of a superconducting film (s), a layer of normal metal (N ) with spin–orbit interaction, and a monodomain ferromagnetic film (F). It is assumed that the S and s materials are superconductors with conventional S-wave pairing potential; in the N layer, two types of spin–orbit scattering (Rashba and Dresselhaus types) coexist [ 50 , 51 , 59 , 60 ]; the direction of the magnetization vector of the upper F layer lies in the plane and can form an arbitrary angle with the direction .…”