Tunable creation of pure spin supercurrents via Rashba spin-orbit coupling with Pt/Co/Pt spin sinks

Superconducting spin currents are key to the development of superconducting spintronics and involve the transfer of spin angular momentum via proximity-induced equal-spin triplet states in a singlet superconductor (SC). Recently developed theory and experimental results show that spin-orbit coupling (SOC) in conjunction with a magnetic exchange field hex generates spin-polarized triplet pairs. Here we demonstrate that when a perpendicularly magnetized Pt/Co/Pt spin sink is proximity-coupled to Nb (a singlet SC), spin-pumping efficiency in the superconducting state is tunable by controlling the tilt angle {\theta}Co of the Co layer magnetization, thus increasing the degree of orthogonality between the SOC and hex at the Nb/Pt/(Co/Pt) interface. We also disentangle the contribution of interfacial SOC to the {\theta}Co-dependent superconducting spin-pumping efficiency from other contributions by inserting a thin Cu spacer with weak SOC at the Nb/Pt/(Co/Pt) interface and find a sinusoidal maximum at {\theta}Co = 45{\deg}, reflecting the characteristic features of Rashba SOC-induced triplet pairing.